Habitats of larger foraminifera on the upper reef slope of Sesoko Island, Okinawa, Japan

ELSEVIER Marine Micropaleontology 36 (1999) 109–168

Habitats of larger foraminifera on the upper reef slope ofSesoko Island, Okinawa, Japan

Johann Hohenegger a,Ł, Elza Yordanova a, Yoshikatsu Nakano b, Franz Tatzreiter a

a Institut fur Palaontologie, Geozentrum, Universitat Wien, Althanstraße 14, A-1090 Vienna, Austriab University of the Ryukyus, Tropical Biosphere Research Center, Sesoko Station, Motobu, Okinawa 905-02, Japan

Received 15 July 1998; accepted 24 November 1998

Abstract

Larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off Sesoko Island, Japan showstrong habitat differences. This study closely examines the distributions of larger foraminifers and relates these to a numberof key environmental factors using rigorous statistical methods. Since all larger foraminifera house symbiotic algae, lightattenuation by the water column is the most important limiting factor that must be dealt with wall structures. Waterenergy is also countered by test structure. The local topography is responsible for different intensities of hydrodynamicforces, which are expressed in various substrates, mostly coral rubble and coarse-grained sand. The genus Peneroplis,very common on the reef flat, clearly prefers hardgrounds of the shallowest slope parts down to 30 m, while Dendritinais restricted to sandy bottoms and avoids the uppermost meters of the slope. It can be found down to 50 m at least.Alveolinella shows a similar depth distribution to Dendritina, but is common on hard bottom. The distribution ofParasorites, which is restricted to sandy substrates, starts at 20 m and extends to 80 m. Sorites, on the other hand, wasfound only on firm substrates between the reef edge and 50 m. The same depth distribution was recorded for Amphisorus,but this genus is not correlated with specific substrates. Most of the Amphistegina species prefer hardgrounds, whileAmphistegina radiata is also common on sand. The calcarinids, capable of withstanding high water energy, are abundanton firm substrates close to the reef edge. Only Baculogypsinoides inhabits deeper parts of the slope on sandy bottom andavoids the shallowest parts. Sections with hard substrates are settled by Heterostegina, even down to 80 m, although thisgenus was occasionally found on sandy bottoms. Nummulites, in contrast, is restricted to sands between 20 and 70 m.Operculina, starting at 20 m, also prefers sandy substrates, but rare individuals were detected on coral rubble and macroids. 1999 Elsevier Science B.V. All rights reserved.

Keywords: Recent; larger foraminifera; habitat; reef slope; West Pacific

1. Introduction

Larger foraminifera are important elements ofbenthic communities in shallow subtropical and trop-

Ł Corresponding author. Fax: C43 (1) 31336784; E-mail:[email protected]

ical seas. They inhabit marine environments startingfrom the intertidal down to the base of the euphoticzone. The restriction to the photic zone is due tothe fact that these foraminifers house symbiotic al-gae which provide the host–symbiont system withadditional energy (Hallock, 1981). This explains thepredominance of larger foraminifers in oligotrophic,

0377-8398/99/$ – see front matter 1999 Elsevier Science B.V. All rights reserved.PII: S 0 3 7 7 - 8 3 9 8 ( 9 8 ) 0 0 0 3 0 - 9

110 J. Hohenegger et al. / Marine Micropaleontology 36 (1999) 109–168

calcium carbonate saturated, and nutrient-depletedenvironments characteristic of tropical and subtrop-ical seas surrounding islands, where the input ofnutrient-rich terrigenous material is poor (Hallock,1985).

Beside temperature and salinity, which are themost important gradients in the geographical dis-tribution of larger foraminifers, sediment structure,light intensity, water energy, and food availabilityare the main factors (in decreasing order) responsi-ble for the local distributions of larger foraminifers(Hottinger, 1988). Some species need food as anadditional source of energy (e.g., Amphisorus andAmphistegina, Lee et al., 1991), but others seem tobe completely independent of food uptake (e.g., Het-erostegina, Rottger, 1976; Calcarina, Rottger andKruger, 1990). Influence of light intensity, water en-ergy and substrate are reflected in test form and wallstructures (e.g., Hallock et al., 1986; Pecheux, 1995),which change within a species in correspondenceto the environmental factors. Communities of largerforaminifera also change along ecological gradients.The depth factor in particular, as a typical compositeenvironmental factor, leads to gradual successions ofcommunities (Hottinger, 1983a, 1997) termed ‘coen-oclines’ (e.g., Hohenegger, 1995).

Most of the work on depth distributions has beenconducted on empty tests (e.g., Reiss and Hottinger,1984; Debenay, 1988). This provides a vague im-pression about the ecological requirements of largerforaminifers by only differentiating between “highwater energy=hard substrate” and “low water ener-gy=soft substrate” forms (Hottinger, 1983a). Thehabitats of only a few genera have been investigatedin detail, such as Amphisorus (Hottinger, 1977a),Sorites (Kloos, 1980), Heterostegina (e.g., Rottger,1976), Calcarina (Rottger and Kruger, 1990), andvarious species from the Caribbean (Hallock andPeebles, 1993). Hohenegger (1994, 1996) recognizedclear differences in larger foraminiferal habitats onnorthwest Pacific reef flats and in lagoons. Speciesinhabiting the reef slope were also investigated, butthese studies were unable to provide sufficient infor-mation on the environmental factors. Since distribu-tions of larger foraminifers on the slope are charac-terized by areal patchiness and can differ remarkablywithin distances of as little as 1000 m, a compre-hensive study of environmental factors is required to

understand the habitats, relations, and differences oflarger foraminifera living on reef slopes.

2. Location and methods

Sesoko Jima is a small island situated to the westof Motobu-Peninsula, Okinawa, Ryu Kyu Island Arch(Fig. 1). A fringing reef surrounds this island, which isseparated from Motobu Peninsula by an 800 m narrowchannel of 10 m depth (Fig. 2). This channel connectsthe southwestern part of Motobu-Peninsula exposedto the China Sea with a small lagoon of maximum19 m depth located northeast of Sesoko. A series ofpatch reefs borders this lagoon to the west, connect-ing the northern fringing reef of Sesoko with the largereefs developed west and north of Cape Bise, the ter-minal point of Motobu Peninsula. The geology of thisregion, where two tectonical zones — the Iheya andNakijin zones — are in contact (Ujiie and Nishimura,1992), creates a complex submarine morphology af-fecting water circulation. A huge submarine glacial-age terrace and depths between 50 and 70 m connectsSesoko-Jima and Motobu Peninsula on the one sidewith Ie-Jima on the other. This platform is borderedto the southwest by a steep slope with a minimumdepth of 90 m between Sesoko and Minna Island. Itcreates a funnel-shaped entrance for currents comingfrom the south and leaving the area between MinnaJima and Nakanose, a small reef exposed only duringlow tide, to the west.

Two transects were chosen northwest off Sesoko-Jima (Fig. 2) according to their different environ-mental conditions. The northern transect starts at theedge of the 135 m wide fringing reef developed inthe northern part of Sesoko. The uppermost part ofthe slope down to 30 m represents the zone of actualreef growth and is relatively steep (mean D �6.1º),followed by a section with minor inclination (meanD �2.4º) down to 60 m, where the flat submarineplatform starts (mean D �0.2º). The southern tran-sect, here called B-transect, is more exposed to theopen sea. It starts at the widest point of the reefplatform (320 m). The inclination in the upper partis similar to the northern transect (mean D �5.3º),but continues in steepness down to 60 m (mean D�3.5º), followed by a pronounced steeper section(mean D �10.5º).

J. Hohenegger et al. / Marine Micropaleontology 36 (1999) 109–168 111

Fig. 1. Location of investigation area.

3. Sampling and preparation

Sampling was processed during June and July1996, and finished just before the first tropical cy-clone (number 9 of the 1996 typhoons) struck Ok-inawa. Thus, all samples represent non-transportedliving foraminifers. Transportation down or even upthe slope can be expected for living individuals dur-ing tropical storms.

Samples were taken by SCUBA in 10 m intervalsdown to 40 m depth, starting at 10 m. Shallowestsamples were collected at 3 m in the northern andat 5 m in the southern transect. The percent cover ofliving reef organisms, reef debris or rock, and sandwas estimated at every sampling point. Two samples

of the substrate surface were taken by hand at eachdepth and filled into plastic boxes. One sample con-sisted of coral debris or macroids (Hottinger, 1983b)representing firm substrates, the other contained sand.Light intensity at the surface and every sampling pointwas measured using a LI-COR radiation sensor.

For studying depth distribution, sampling was car-ried out from 50 m down to 100 m depth in bothtransects using a dredge consisting of an iron tube25 cm in diameter with a jute sack fixed at oneend. Differences in substrate preferences of largerforaminifera are difficult to detect with dredged sam-ples that contain sandy sediments as well as largercomponents, thus habitat preferences mostly cannotbe recognized. Two dredged samples from 50 m


Fig. 2. Sampling stations and main currents in the investigation area.

depth could be used in the northern transect forhabitat investigation on two reasons: one consistedof sand exclusively, the other of larger coral de-bris and rodoliths. In the southern transect, only onesandy sample was dredged from 50 m depth; it wasused as a representative for sandy bottoms. One oftwo samples from 60 m depth contained numerousmacroids (>40%) and was used to calculate forami-niferal abundance on firm substrates at 50 m depth inthe southern transect.

Investigation in the laboratory was performedafter filling the samples into high-walled glassbowls. Larger components, such as coral rubble andmacroids, were examined under the stereomicroscope

and brushed afterwards. Only a thin sediment layer(maximum 3 mm) was put into the dishes. After 1day at least, all living foraminifera spread their proto-plasm, containing symbiotic algae, into the terminalchambers and they often climbed to the surface. Thus,they could be easily recognized by their colouring,picked out with fine forceps and put into smaller petridishes. Since all the living individuals cannot climb tothe surface within one day, this treatment was repeatedafter disturbing the sediment layer. Approximatelyhalf the number of living foraminifers recognized inthe first treatment was detected the second time.

Living forms were washed with freshwater anddried. Dried specimen retain their symbiont-induced


colour. The remaining sediment was stored for inves-tigation of empty foraminiferal tests and sedimentanalyses.

4. Data analysis

After determination and sorting, species abun-dance and test size were measured by two methodsusing an image analyzer Kontron Elektronik Imag-ing System KS 400. The commonly used parameterfor habitat preferences, ‘number of individuals’, canbe biased by reproduction rates of foraminifera withfixed breeding seasons (e.g., Zohary et al., 1980).Strong fluctuations of specimen numbers occur insteady state populations, which are typical popu-lation structures for the larger foraminifers. Sincebiomass remains more constant during a discontin-uous reproduction cycle than specimen number andshows fewer deviations from an average amount,test sizes of larger foraminifera were used to ap-proximate this parameter. Simple measures of size,like the ‘largest’ or ‘shortest test diameter’, dependstrongly on form. Especially in species where testform changes during growth, e.g., Peneroplis witha planispiral initial coil and a uniserial, rectilin-ear, sometimes flaring final part, these measurementscannot sufficiently express biomass. The contourarea of the test was used in the following, becauseit lacks only height to measure test volume, whichseems to be the best approximation to biomass usingforaminiferal tests.

Normalization of different sample sizes was per-formed to compare frequencies. Both parametersused here — ‘specimen number’ and ‘sum of con-tour areas’ — were normalized to a sediment weightof 500 g, which is close to the average sample weightof 600 g (Tables 1 and 2). This greatly reduces thebias of normalization, which is often effected byextreme differences in starting and target quantities.Normalization to a standard sediment weight is notproblematical for sandy substrates, since all sam-ples show similar grain size distribution effected byhabitat conditions. In contrast, cobbles (as a grainsize class, see Stoddart, 1978) consisting of organiccarbonate with identical weight can differ in sizeand form (e.g., branched coral pieces of Acroporaversus large macroids) depending on their sources

and exposition to water movement. In the following,‘surface area’ and ‘surface form’ of cobbles, whichare important for the settlement of foraminifera bygiving rise to various modes of fixation, may alsodiffer despite identical component weights. The ‘re-gional form factor’ relating the contour area to thesquared perimeter was measured on the x–y andx–z plane to obtain a three-dimensional approxima-tion of the surface parameters mentioned above (e.g.,Batschelet, 1971).

Since samples were taken at two transects andseparated into soft and firm substrates accordingto sediment differences, further analyses of specieshabitat compare these four frequency distributionsalong the depth gradient. Abundance at the missingsample from 50 m of the southern transect wascalculated using cubic spline functions. Here, thesample collected by SCUBA down to 40 m wascombined with a dredged sample of 60 m depthconsisting of 40% macroids.

In a first step, correspondences of distributionforms between ‘specimen number’ and ‘sum of con-tour areas’ along the depth gradient were tested usinglinear regression (Table 3). Except for two species, theanalyses demonstrate strong correlation, confirmedby extremely significant regression coefficients. Theconstants within these regression functions are almostnot significant, indicating regression through the ori-gin, which is a basic requirement for the comparisonof distribution forms using regression analysis. In thiscase, regression coefficients can be substituted by theratios between ‘sums of contour areas’ and ‘speci-men number’, representing an average contour areafor each species at the sample point. Comparison ofthese averages among the four frequency distributionswas performed using ‘one-way analysis of variance’(Table 3). In the case of significant differences, theywere checked by the ‘Duncan-test’. As a result of thestrong correlation between both abundance parame-ters, further investigation was performed only withthe parameter ‘sum of contour areas’, except for thetwo species in which the parameters mismatch.

Comparison of species habitat using the four fre-quency distributions was done similar to the compar-ison of both abundance parameters described above.Correspondence of distribution form was tested byregression analysis through the origin. Abundancedifferences are also expressed in the increase of

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Table 1Frequencies in the northern transect (A-Transect) represented as specimen numbers (normal characters) and contour area (italics in brackets)

Firm substrate

Sample number: 96-40 96-5 96-10 96-15 96-14=16 96-9 96-11 96-2Sediment weight (g): 985.8 174.8 765 831.9 1144.95 581.75 531 338.9Depth (m): 4 10 20 20 30 30 40 50

Peneroplis antillarum 112 (14.48) 2 (0.49) 2 (0.55) 27 (5.51) 12 (3.19) – 2 (0.78) –Peneroplis planatus 4 (0.88) 43 (13.17) 3 (1.48) 28 (8.45) 11 (3.44) – 11 (3.29) –Peneroplis pertusus 16 (3.24) 9 (3.67) 4 (1.22) 18 (4.86) 18 (5.06) 4 (1.96) 11 (4.65) –Dendritina ambigua – 3 (0.93) – 4 (1.69) 1 (1.00) 1 (0.17) – –Dendritina zhengae – – – 1 (0.21) – 1 (0.62) – –Dendritina cf. zhengae – – – 2 (0.53) 6 (1.59) – – –Alveolinella quoyi – 12 (41.73) 4 (6.76) 11 (27.62) 12 (22.75) 7 (20.37) 6 (22.20) –Parasorites orbitolitoides – 1 (0.41) 1 (0.28) 18 (17.79) 15 (13.27) – 4 (1.48) 1 (1.25)Sorites orbiculus 10 (8.20) 35 (41.77) 250 (389.28) 65 (96.81) 154 (185.51) 65 (74.21) 71 (115.37) –Amphisorus hemprichii 7 (6.88) 10 (9.31) 55 (14.56) 33 (12.99) 75 (309.19) 64 (58.22) 27 (175.02) 1 (14.22)Amphistegina lobifera 220 (118.85) 23 (26.99) 3 (2.08) 6 (5.43) – 1 (0.91) – –Amphistegina lessonii umbiliconvex 93 (25.57) 2 (1.52) 2 (0.77) 28 (16.54) 7 (3.44) 8 (2.33) – –Amphistegina lessonii biconvex 110 (32.04) 88 (33.23) 104 (34.77) 342 (112.46) 132 (45.64) 108 (32.18) 73 (35.28) 4 (4.79)Amphistegina radiata 1 (0.22) 57 (73.93) 131 (206.54) 352 (394.90) 144 (181.49) 58 (51.73) 37 (43.03) 13 (23.69)Neorotalia calcar 22 (9.449) 3 (0.94) – – – – – –Calcarina gaudichaudii 350 (387.75) 5 (19.89) 3 (7.69) 2 (4.93) 1 (1.04) – – –Calcarina defrancii 1 (0.78) 19 (15.43) 1 (0.81) 9 (6.29) 3 (1.71) – – –Calcarina hispida form defrancii – 8 (6.54) 25 (13.46) 307 (162.46) 359 (199.08) 98 (66.99) 223 (131.11) 76 (55.18)Calcarina hispida form spinosa 63 (72.96) 487 (793.68) 23 (24.16) 796 (806.95) 159 (200.62) 2 (4.06) 34 (39.94) 18 (8.46)Baculogypsinoides spinosus – – 34 (18.54) 18 (10.22) 54 (40.85) 10 (16.49) 33 (35.09) 48 (121.75)Baculogypsina sphaerulata 6 (3.92) – – – 1 (1.26) – – –Operculina ammonoides – 4 (10.84) 8 (17.06) 16 (24.49) 84 (146.80) 13 (12.88) 51 (83.22) 30 (54.59)Nummulites venosus – – – – 1 (3.89) – 1 (2.97) 11 (30.95)Heterostegina depressa 5 (8.09) 22 (49.72) 75 (133.31) 106 (190.18) 146 (440.73) 30 (63.06) 38 (124.85) 33 (213.76)

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Table 1 (continued)

Soft substrate

Sample number: 96-39 96-15 96-10 96-14=16 96-9 96-11 96-1Sediment weight (g): 679.3 477.8 480.6 1125.4 499.4 463.2 570.6Depth (m): 4 20 20 30 30 50 50

Peneroplis antillarum 1 (0.44) – – 1 (0.20) – – –Peneroplis planatus – 6 (1.13) 1 (0.67) 2 (1.60) – – –Peneroplis pertusus 1 (0.32) – 3 (0.91) 11 (2.78) 1 (1.24) 1 (0.56) –Dendritina ambigua – 194 (51.56) – 20 (10.76) 16 (13.13) – –Dendritina zhengae – 33 (10.57) – 18 (5.90) 2 (0.95) 1 (0.88) 2 (1.45)Dendritina cf. zhengae – 60 (20.14) – 25 (7.62) – – 4 (4.28)Alveolinella quoyi – – 3 (8.88) 3 (8.97) – – 1 (4.60)Parasorites orbitolitoides – 244 (199.79) 7 (4.37) 102 (91.76) 56 (77.12) 16 (32.1) 11 (32.31)Sorites orbiculus – 2 (2.11) 8 (9.03) 10 (13.66) 3 (2.60) 1 (0.45) 2 (7.14)Amphisorus hemprichii – – – 11 (31.59) 29 (67.49) 3 (57.87) 4 (47.57)Amphistegina lobifera 11 (7.80) 12 (8.29) 1 (1.27) – 2 (2.95) – –Amphistegina lessonii umbiliconvex 6 (1.29) 325 (133.93) 3 (1.31) 29 (20.48) 21 (8.75) – 4 (4.75)Amphistegina lessonii biconvex 7 (2.33) 16 (10.81) 14 (8.98) 22 (10.19) 19 (11.32) 5 (4.04) 17 (14.41)Amphistegina radiata 2 (1.80) – 36 (52.79) 37 (27.60) 9 (4.59) 7 (4.62) 13 (11.86)Neorotalia calcar 5 (3.19) – – 1 (0.23) – – –Calcarina gaudichaudii 50 (100.26) – 1 (2.89) – – – –Calcarina defrancii 1 (0.79) 1 (1.30) – – – – –Calcarina hispida form defrancii 21 (16.12) – 68 (42.46) 16 (10.74) 11 (9.40) 27 (18.6)Calcarina hispida form spinosa 4 (3.91) 6 (5.58) – 10 (11.19) – 2 (2.00) –Baculogypsinoides spinosus – – – 8 (6.85) – – 14 (22.61)Baculogypsina sphaerulata 2 (2.27) – – – – – –Operculina ammonoides – 24 (67.46) 10 (21.51) 75 (225.54) 31 (119.62) 22 (65.24) 36 (85.42)Nummulites venosus – 3 (4.78) 1 (5.49) 103 (253.11) 30 (88.92) 14 (34.71) 87 (233.73)Heterostegina depressa 11 (23.09) 2 (9.98) 12 (110.27) 18 (67.92) 9 (46.78) 3 (9.15) 6 (38.01)

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Table 2Frequencies in the southern transect (B-Transect) represented as specimen numbers (normal characters) and contour area (italics in brackets)

Firm substrate Soft substrate

Sample number: 96-8 96-7 96-13 96-12 96-18 96-29 96-8 96-7 96-13 96-12 96-18 96-19Sediment weight (g): 767.25 788.5 1032.5 746.25 1240.56 411.6 366.2 456.8 618.2 1753.33Depth (m): 5 10 20 30 40 60 5 10 20 30 40 50

Peneroplis antillarum – 1 (0.19) 5 (0.56) 2 (0.31) – – – – 1 (0.11) – – –Peneroplis planatus 34 (17.13) 83 (31.80) 29 (9.77) 4 (1.46) – – 3 (1.58) 6 (2.78) 2 (1.00) 2 (0.50) – –Peneroplis pertusus 2 (1.55) 6 (2.86) 13 (3.69) 13 (5.15) 7 (2.89) – – 6 (3.45) 6 (4.00) 11 (5.27) 2 (0.66) –Dendritina ambigua 1 (0.18) – – – – – – – 18 (6.22) 5 (5.13) – –Dendrtina zhengae – – – – – – – – 28 (8.91) – – –Dendritina cf. zhengae – – – – – – – – – 1 (0.70) – –Alveolinella quoyi – – – 3 (7.99) 2 (0.30) – – – 1 (3.06) 3 (8.53) 2 (0.71) –Parasorites orbitolitoides – – 1 (0.33) 6 (3.87) 45 (29.07) 2 (5.84) – – 41 (35.34) 24 (15.85) 87 (106.37) 5 (4.72)Sorites orbiculus 16 (22.00) 100 (148.93) 85 (90.68) 87 (102.15) 4 (6.44) 1 (0.57) 1 (1.17) 6 (11.02) 9 (8.62) 15 (20.94) 2 (2.01) 1 (0.81)Amphisorus hemprichii 2 (0.59) 8 (71.56) 31 (11.04) 35 (114.09) 12 (4.08) – 1 (35.39) 3 (54.98) 4 (2.91) 6 (4.50) 25 (23.69) 1 (0.41)Amphistegina lobifera 12 (11.66) 283 (298.17) 13 (11.36) 10 (10.27) – – 83 (88.24) 44 (41.95) 5 (3.77) 30 (29.07) – –Amphistegina lessonii umbiliconvex 3 (0.54) – 5 (1.31) 4 (1.01) 61 (19.05) – – 2 (0.46) 36 (18.51) 54 (24.05) 39 (16.54) 20 (6.85)Amphistegina lessonii biconvex 8 (2.57) 318 (123.96) 263 (86.83) 416 (138.89) 321 (78.54) 13 (4.48) 1 (0.35) 18 (9.57) 26 (17.14) 102 (63.42) 12 (9.77) 28 (11.68)Amphistegina radiata 1 (0.39) 46 (57.94) 157 (215.49) 245 (272.86) 592 (779.69) 71 (95.99) 6 (14.40) 5 (10.86) 14 (19.10) 57 (62.75) 90 (102.52) 181 (172.22)Neorotalia calcar 2 (1.32) 1 (0.87) – 1 (0.82) – – – 1 (0.67) – – – –Calcarina gaudichaudii 8 (21.81) 1 (0.47) 1 (1.45) 2 (5.10) – – – – – – – –Calcarina defrancii – 3 (2.66) 9 (5.57) 3 (3.16) – – – – 1 (0.64) 2 (1.89) – –Calcarina hispida form defrancii – – 3 (1.24) 33 (25.26) 10 (8.02) 1 (0.90) – – – – – 1 (1.33)Calcarina hispida form spinosa – 2 (1.08) 12 (18.98) 8 (4.39) – 16 (11.83) – – – – – –Baculogypsinoides spinosus – – 4 (3.21) 3 (3.05) 48 (113.45) 49 (95.76) – – – 1 (3.23) 6 (23.16) 2 (6.04)Baculogypsina sphaerulata – – – – – – – – – – – –Operculina ammonoides – – 12 (7.72) 18 (8.90) 27 (26.48) 202 (662.66) – – 3 (8.82) 42 (161.35) 77 (250.61) 67 (205.49)Nummulites venosus – – – 3 (4.75) 2 (1.02) 1 (4.18) 1 (1.57) – 2 (6.21) 67 (192.10) 31 (92.27) 78 (160.85)Heterostegina depressa 4 (2.66) 28 (59.17) 109 (165.98) 102 (145.02) 159 (349.00) 39 (376.31) 44 (128.88) 17 (61.08) 37 (137.94) 31 (195.93) 36 (166.20) 33 (177.13)


Table 3Relations between contour areas and specimen numbers tested by linear regression

Northern Transect Southern Transect Probability

firm soft firm soft

Peneroplis antillarum regression coeff. 0.124 0.392 0.115 0.110area=number 0.247 0.342 0.152 0.110 0.1198

Peneroplis planatus regression coeff. 0.307 0.186 0.390 0.479area=number 0.288 0.418 0.397 0.435 0.5092

Peneroplis pertusus regression coeff. 0.412 0.253 0.234 0.570area=number 0.317 0.282 0.458 0.513 0.1557

Dendritina ambigua regression coeff. 0.308 0.264 0.180 0.355area=number 0.578 0.360 0.180 0.686 0.5715

Dendritina zhengae regression coeff. 0.210 0.305 0.318flat form area=number 0.210 0.515 0.318 0.5629

Dendritina zhengae regression coeff. 0.265 0.322 0.700lenticular form area=number 0.265 0.510 0.700 0.5544

Alveolinella quoyi regression coeff. 3.504 3.335 1.379 2.428area=number 2.897 3.795 0.938 2.086 0.1353

Parasorites orbitolitoides regression coeff. 1.101 0.752 0.655 1.132area=number 0.781 1.499 0.598 0.922 0.1278

Sorites orbiculus regression coeff. 1.261 1.308 1.219 1.359area=number 1.267 1.311 1.343 1.196 0.9872

Amphisorus hemprichii regression coeff. 3.159 8.807 1.360 -0.723area=number 4.522 11.351 2.199 9.425 0.4020

Amphistegina lobifera regression coeff. 0.697 0.694 1.054 1.043area=number 0.873 0.698 0.982 0.935 0.1984

Amphistegina lessonii regression coeff. 0.291 0.408 0.314 0.479umbiliconvex form area=number 0.529 0.588 0.259 0.391 0.1429

Amphistegina lessonii regression coeff. 0.339 0.801 0.298 0.630biconvex form area=number 0.504 0.608 0.316 0.566 0.1353

Amphistegina radiata regression coeff. 1.156 0.769 1.299 0.943area=number 1.147 0.805 1.102 1.521 0.1505

Neorotalia calcar regression coeff. 0.385 0.645 0.681 0.670area=number 0.371 0.494 0.783 0.670 0.1364

Calcarina spengleri regression coeff. 1.088 2.005 2.779area=number 2.148 2.005 1.800 0.9110

Calcarina defrancii regression coeff. 0.813 0.808 0.634 0.857area=number 0.715 0.859 0.853 0.793 0.8605

Calcarina hispida regression coeff. 0.550 0.641 0.772 1.133form defrancii area=number 0.643 0.724 0.753 1.330 0.0194

Calcarina hispida regression coeff. 1.588 0.971 1.380form spinosa area=number 1.118 1.005 0.890 0.6737

Baculogypsinoides spinosus regression coeff. 2.442 1.610 2.832 3.856area=number 1.231 1.236 3.394 3.370 0.4986

Baculogypsina sphaerulata regression coeff. 0.649 1.067area=number 0.957 0.946 0.9786

Operculina ammonoides regression coeff. 1.637 2.766 2.619 3.374area=number 1.888 2.816 1.206 3.276 0.0007

Nummulites venosus regression coeff. 2.806 2.659 0.436 2.858area=number 3.225 2.304 0.832 2.516 0.0034

Heterostegina depressa regression coeff. 1.873 2.142 2.124 2.346area=number 3.076 3.848 1.892 4.426 0.0330

Bold numbers mark significant regression coefficients (error probability <5%) and insignificant constants. Italics denote significantconstants indicating no regression through the origin. Homogeneity of the area=number ratio is tested for each species using one wayanalyses of variance and represented in probabilities.


the regression line, but in case of lacking corre-spondence, this parameter is not useful. Since mostof the data are not normally distributed, abundancedifferences had to be examined by nonparametrictests. First, homogeneity of species abundance in-cluding all distribution functions was checked usingthe ‘Friedman two-way analysis of variance’ for tiedsamples. In most cases, this analysis showed signifi-cant differences, which were checked by a pairwisecomparison between samples using the ‘Wilcoxonmatched-pairs signed-ranks test’.

Results are presented for every species in formof triangular matrices with an ordering of transectsaccording to their total species abundance (C panelsin Figs. 7–27, 28, 29 and 30). The right upper trian-gular matrix contains probabilities of non-correlationin distribution form as gained by regression throughthe origin. Shaded areas mark significant correspon-dences in distribution form with an error probabilityless than 5%. The lower left triangular matrix con-tains the regression coefficients, which in case ofsignificant correlations are good approximations ofproportions between samples labelling the matrixrow to samples heading the column. In this triangu-lar matrix, significant differences as determined bythe ‘Wilcoxon test’ are marked by non-shaded areas(error probability <5%).

Since foraminiferal tests grow exponentially orfollow a logistic curve, fitting of test size distribu-tions by theoretical normal and lognormal distribu-tions was performed in every species for total speci-mens and different depth populations. These fits weresubsequently tested by the ‘Chi-square statistic’ orthe ‘Kolmogoroff–Smirnov Test’. In case of non-sig-nificant fitting by either a single normal or lognormaldistribution, decomposition into lognormally or nor-mally distributed subpopulations was exercised.

All statistical analyses were processed using theprogram packages SPSS 7.5 and Statgraphics Plus2.0 for Windows.

5. Environmental setting

5.1. Light

Light is the most important factor affecting thedistribution of larger foraminifera, since all house

symbiotic algae. Irradiance was measured duringsampling by SCUBA. This was done at noon underfair weather conditions yielding maximum irradi-ation values just below the water surface becauseof solar altitude. Nevertheless, differences occurredbetween both transects despite identical weather con-ditions, whereby the northern transect had the highervalues (average 2050 µE m�2 s�1) versus the south-ern one (average 1750 µE m�2 s�1). These differ-ences may be caused by a rougher surface in thesouthern transect, where waves are stronger becausethe main summer wind direction is from the south(Fig. 2). The decrease in light availability with depthfollowing Beer’s law is characterized by a low meanattenuation coefficient of 0.0469 in the southerntransect, which is typical for clear subtropical oceanwater (Fig. 3). The much higher value (0.0641) inthe northern transect may be caused by the moresuspended particles. Finally, average light intensitiesof 190 µE m�2 s�1 were observed at both deepestsampling points (40 m).

Seasonal change of solar irradiation leads to dif-ferences in light availability. The decrease throughweather conditions in the cold season may be com-pensated by a higher amount of suspended particlesor dissolved substances during the hot season. Thiswill be caused both by the production climax oforganisms in early summer and by high suspensionthat occurs for more than two weeks after a tropi-cal storm. Over the whole year, transparency of theocean water is much higher in winter and spring thanin summer or autumn (Sakai et al., 1984, 1986).

5.2. Temperature

Water temperature is important for coral reefgrowth and larger foraminifers. The high geographi-cal latitude (26º390) of Sesoko Island and its proxim-ity to the Asian continent leads to variable air tem-peratures. The range of mean daytime temperaturesshows a minimum of 15ºC in February and a max-imum of 31ºC in August (Nakano and Nakamura,1993a,b, 1993c), but this affects only the surface seawater. Water temperature is less influenced a fewmeters below the surface and is compensated by thewarm Kuroshio current, which passes Okinawa onits west, flowing in NE direction. A branch of thiscurrent enters the area at the funnel-shaped entrance


Fig. 3. Attenuation on sunny mid-days in June 1996.

between Sesoko and Minna-Jima described aboveand exits to the northwest and north.

Annual temperature variation do not differstrongly from 5 to 20 m and demonstrate similartrends, showing a minimum between 20 and 21ºCin February, and a maximum of 28 to 29ºC in Julyand August. Temperatures at 30 m are almost con-gruent with the former from summer until earlyspring. Starting in May and continuing until thefirst half of July, when temperatures at the shal-lower depth strongly increase, a thermocline of 1ºCdevelops between 20 and 30 m. At 50 m the tem-perature increases significantly in late July, leadingto temperatures that are only 2.5ºC below those ofthe overlying water, which continues until October,

when these differences vanish after the shallowerwater cools.

5.3. Waves and currents

Waves affect the seafloor depending on wind forceand bottom depth (e.g., Hiscock, 1983). The mainwind directions show a seasonal change, but onlydirections from north to east and south are im-portant. Northeastern winds dominate from autumnuntil spring. At the onset of the rain season due to thetropical monsoon cross in May, southern winds pre-dominate during summer until the back crossing ofthe tropical front in September (Fig. 4). The monthlywind forces remain constant through the year (me-


Fig. 4. Wind directions and wind force in 1996 (unpublished data by Nakano; fit of circular histograms by decomposition into Von Misedistributions).


dian D 3), showing the weakest values in October(mean D 1.83). Most of these monthly frequencydistributions are symmetrical with similar standarddeviations. This is confirmed by low values of pos-itive skewness, indicating that wind forces above 6are rare. Tropical cyclones sometimes produce max-imum wind force during summer (50.2 m s�1 asmaximum of the typhoon #12 on August 13, 1996),depending on their course and position relative to theisland. Their influence is reflected by the distribu-tion parameters in so far as the standard deviationsbecome higher and skewness becomes significantlyright-sided (Fig. 4).

These main wind directions cause different con-ditions for bottom sediments in the two localities.Both areas experience weaker waves in winter andspring, since they are protected against northeasternwinds by their leeward position to Okinawa Island.Nevertheless, waves are higher in the northern tran-sect due to its open position to the North betweenIe-Jima and Cape Bise, while the southern transectis protected by the fringing reef of Sesoko Island.Stronger differences in wave size between both tran-sects occur during summer, where waves from thesouth directly strike the reef slope of the southerntransect. The shallower parts of the northern tran-sect are protected against these wind-induced cur-rents. Significant nearbed oscillatory velocity (His-cock, 1983) down to 15 m depth can be expectedin winter months, acting strongly in the northernpart. During summer, the wave base increases to20 m depth, where more or less intensive motioncan be expected for the bottom of the southern tran-sect, since southern winds create constant currents.The northern transect is protected against these cur-rents by its leeward position behind the fringingreef.

Fringing reefs in Okinawa lack channels connect-ing the reef moats and fore reef areas (Yamanouchi,1993). Since the fringing reef of Sesoko is a spur andgroove system only (Yamazato et al., 1974), tidalcurrents seems to be less important in the southernpart of the investigation area. The northern transect,on the other hand, is positioned close to an outlet ofthe lagoon northeast of Sesoko Jima, which is sep-arated from the fore reef slope by a series of patchreefs. Tidal currents may therefore influence the bot-tom of the northern transect below the fair weather

wave base down to 100 m depth and are responsiblefor the input of suspended material from the lagoon.

The Kuroshio current flowing in the East ChinaSea from southwest to northeast passes Okinawa tothe west. Sesoko Jima divides parts of this currentinto two branches (Fig. 2). Velocities of the mosteastern branch are intensified by the funnel-shapedentrance between Sesoko-Jima and Motobu Penin-sula, where the waterway connecting the lagoonnortheast of Sesoko Island with the open sea narrowsto 800 m may be as shallow as 10 m. This currentleaves the lagoon (maximum depth 19 m) through10 m deep channels between patch reefs borderingthe lagoon on its west side and is strengthened bytidal currents during ebb tide.

5.4. Substrate

Differences in water energy of both transects atvarious depths are reflected in sediment composi-tion. All sediments consist of organic carbonates;terrestrial influences are restricted to the lagoon area(Ujiie and Shioya, 1980). Breakage and damaging ofcarbonates are mainly caused by hydraulic energy infore reef areas, with additional destruction of coralreefs by parrot fishes (Gygy, 1975). Thus, grain sizemainly reflects water energy in these environments.

The spurs of the reef platform are densely coveredby tabular Acropora. Broken coral pieces cover thegroove’s bottom, where patches of coarse grainedsand accumulate in protected parts. Due to variationsin exposition to water energy, both transects showdifferences in composition of living corals, coralrubble or empty rock, and sandy bottom from 5 to50 m depth (Figs. 5 and 6). The large number ofliving corals (staghorn forms of Acropora are domi-nant) slowly decreases in the northern transect withdepth, yet retains a high proportion of 40% at 40 m(Fig. 5C). Most of the remaining substrate consistsof empty rock, coral rubble or rodoliths. Only 20%sand is observed at 40 m. The proportion of livingcorals decreases more rapidly in the southern tran-sect, falling to 30% at 10 m depth (Fig. 6C). Thisis followed by a gradual decrease, with all livingcorals disappearing at 40 m depth. Therefore, thesediment in the upper part of the southern transectdown to 25 m consists largely of coral rubble andmacroids, replaced in the deeper parts by sand. The


latter dominates at 50 m in the B-transect (90%),while in the northern transect (70% sand) numerousmacroids cover the sandy bottom at this depth.

Components of cobble size demonstrate a signif-icant relation to water depth only in the northerntransect (Fig. 5A). The decrease in size is provenby simple linear regression starting with a meancontour area of 2090 mm2 at the reef edge. Theregression coefficient (b D �12:60) is lower thanthe coefficient in the southern transect, indicating aslighter but still significant decrease. Cobbles at thereef edge in the southern transect are distinguishedby a mean contour area of 3141 mm2 with a strongerbut insignificant linear decrease (b D �18:78) downto 40 m depth. The ‘regional form-parameter’ relat-ing the contour area of a component to its squaredperimeter significantly increases with depth in thenorthern transect starting with a low mean parametervalue (0.26) at the reef edge and attaining a mean of0.49 at 50 m (Fig. 5B). This value is similar to theparameter mean of 0.43 at the reef edge in the south-ern transect, where an insignificant increase leads toa mean of 0.54 at 50 m (Fig. 6B).

All sands in the investigation area are ‘coarsesands’, showing a mean grain size of 0.56φ in thenorthern and 0.49φ in the southern transect, whichindicates high water energy in both areas (Fig. 5D,Fig. 6D). Standard deviations of these means dif-fer significantly. Sands of the northern transect aremore homogeneous (SD D 0.11). This parameter is5 times higher in the southern transect (SD D 0.53),where the extremes to either side are ‘very coarsesand’ (mean grain size D �0.32φ) and at ‘mediumsand’ (mean grain sizeD 1.27φ). No significant depthcorrelation of mean grain sizes could be detected byregression analyses. Comparing both transects usingthe Wilcoxon test for matched samples resulted in ho-mogeneity. Thus, water energy does not differ signifi-cantly in both transects during the deposition of sands.

The sorting coefficient as a parameter estimatingconstancy in water movement differs in both tran-

Fig. 5. Northern transect. (A) Depth correspondence of the volume of larger components represented in Box-plots. Box lengthD interquartile range; black line D position of the median; whiskers D highest and lowest values; points D outliers. (B) Depthcorrespondence of the ‘regional form factor’ (D contour area=squared perimeter) of larger components represented in Box-plots. (C)Proportions of living corals, larger components, and sand in correspondence to depth. (D) Grain-size distribution of soft sediments incorrespondence to depth.

sects. A mean sorting coefficient of 0.97 indicatesthat sands are ‘moderately sorted’ (Folk, 1974) in thesouthern transect. Thus, they are better sorted thanthe northern transect, where all samples are ‘poorlysorted’ (mean sorting coefficient D 1.27). Resistanceto turbulent water is higher in these sediments due toa better packing. Again, correspondence of sorting todepth is not significant in either transect.

The sediment analyses yield the following con-clusions despite the restricted applicability for inter-pretation of hydrodynamic conditions by carbonatesands due to their low specific weight, skeletal ori-gin, and lower hardness compared with siliciclasts(e.g., Stoddart, 1978; Wright, 1990). The uppermostreef slope is exposed to wind-induced waves pro-ducing abundant sand by mechanical or biologicalbreakage of carbonate skeletons; this material is de-posited in front of the reef edge. During autumn,winter and early spring the slope acts as a leewardmargin, where finer grained sediment is transportedfrom the lagoon through channels between patchreefs to the northern transect. This may be reinforcedby tidal currents. Some coarse grained sand is trans-ported during high tide and strong winds from theshallow reef moat over the crest to the slope of thesouthern transect. Slope sands are mainly producedby mechanical breakage during late spring and sum-mer, when the investigation area is exposed to south-ern winds and typhoons. Onshore wave and stormcurrents produce strong downslope bottom currents,and accumulation in depths >80 m is additionallycaused by gravity flow processes. The northern areais more protected against wind and storm-inducedwaves during summer, explaining the predominanceof coral rubble. These pieces are crushed to finergrain size by much stronger water energy in thesouthern transect. The greater living coral abundancein the northern transect is probably due to the betterfood availability during the main biological produc-tion period in late spring and summer. This assump-tion is supported by the lower transparency as well


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as the poorly sorted bottom sands (high proportionof fine grains) in the northern transect.

6. Results

Living larger foraminifera belong to two subor-ders based on wall structures. The ultrastructure oftest walls in the first group, the Miliolina, consistsof an irregular arrangement of extremely small, highmagnesium calcite needles. Light is reflected by dis-orientation of the optical crystal axes. Together witha smooth test surface, this results in a porcelaineousappearance. Smaller representatives of this subordercan therefore settle in highly illuminated regions andshield their genetic material from UV-irradiation bythis special wall structure. They are thus abundant intropical and subtropical shallow-water environments,often preferring higher salinity. Larger foraminifersof this group must provide their symbionts with light,developing special mechanisms of wall thinning —such as windows, pits, and grooves — which enablelight penetration. Three families of foraminifera de-veloping larger tests, the Peneroplidae, Alveolinidae,and Soritidae, belong to the suborder Miliolina.

Living larger foraminifera with transparent testsbelonging to the second suborder Rotaliina can alsobe grouped into 3 families, the Amphisteginidae,Calcarinidae, and Nummulitidae. Wall structure dif-fers considerably from the Miliolina in so far asthe rhomboedric, low magnesium calcite crystallitesare oriented with their optical axes either perpen-dicular or with an inclination of 45º to the surface.Thus, light is only weakly broken in penetrating thewalls, and a large amount of photons reaches thesymbionts in the host’s cytoplasm. Special light-col-lecting mechanisms like pustules and nodes, togetherwith a very thin shell, enable these larger foramin-ifers to settle below the base of the photic zone,where the symbionts — mostly diatoms — can stillphotosynthesize. UV-irradiation in shallowest envi-ronments is blocked by thickening test walls withlamellae. The main purpose of such lamellae is tostrengthen the test against mechanical stress in highenergy environments.

Species are classified strictly following the ‘eco-logical species concept’ (Van Valen, 1976), whichregards homogeneities in ecological niches as the

main criterion for species definition. Recognitionof species involves detecting morphological homo-geneities within and heterogeneities between groups.Frequency distributions along an environmental gra-dient characterize the response of species to theirecological niche and can be used to differentiate be-tween ecophenotypes and species. A homogeneousfrequency distribution showing continuous transi-tions between various ecophenotypes cannot be sep-arated by objective criteria. Generic names shouldreflect phylogenetic relationship between species andare given according to the present status of forami-niferal classification.

On the one hand, test size frequency distributionsof a species indicate growth stages within a pop-ulation, thus characterizing population structure; onthe other hand, they mark different generations or co-horts. In the case of unimodal distributions they oftencan be fitted by lognormal functions. This is due ei-ther to logarithmic test growth in populations withdistinct breeding seasons showing more or less sim-ilar age but different growth rates (e.g., cyclic testsof Amphisorus hemprichii), or to the predominanceof younger individuals in more or less continuouslybreeding populations. Additionally, superposition ofdifferent reproductive generations with small differ-ences in their means also causes right-side (in afew cases left-side) skewed distributions, dependingon their proportion. Obvious test size differences inlarger foraminifers leading to multimodal distribu-tions are mostly based on generation differences, buta sequence of cohorts can not be excluded, especiallyin forms with more than one seasonally induced re-productive cycle (e.g., annual asexual reproductionin June–July with 18 months longevity in Baculo-gypsina sphaerulata, Sakai and Nishihira, 1981). Atrimorphic cycle is proven in some larger forami-nifera. Distinction between agamonts and gamontsis always expressed in proloculus size. Small prolo-culi, sometimes combined with extremely large tests,always indicate agamonts. Schizonts and gamontscan not be differentiated by proloculus size, but theymay differ in test size (e.g., Heterostegina depressa,Rottger et al., 1990a). Since proloculus size was notmeasured in the following analyses, biological inter-pretation of most multimodal or left skewed test sizedistributions are difficult.


Fig. 7. Test size distribution (A) and habitat (B and C) of Peneroplis antillarum d’Orbigny. (A) Test size distributions. (B) Depth dis-tributions on different substrates. (C) Triangular matrices of form correspondence (right upper triangular matrix containing probabilitiesof non-correlation) and abundance correspondence (left lower triangular matrix containing coefficients of regression through the origin).The four depth distributions ordered by total abundance. Testing of abundance differences by the Wilcoxon matched-pairs signed-ranktest (shaded cells mark significant differences at 5% error propbability).

6.1. Peneroplidae

This family is characterized by porcelaineous wallstructures. Due to the nonlamellar wall construc-tion in all miliolid foraminiferids, lateral thickening,which is necessary to counter high water energyand sediment movement, can only be achieved bytest form. Planispirally enrolled tests with a moreor less rectilinear final part characterize this family.The lack of additional mechanisms for strengtheningthe walls and tests restricts size to less than 2 mm.Rodophyceans, which are indicated by their purplecolor, act as symbionts in all 5 species represented inthe investigation area.

Peneroplis antillarum d’Orbigny (Fig. 7)

This species (in the sense of Gudmundsson, 1994,not Le Calvez, 1977) is characterized by planispi-rally enrolled involute tests with only the last whorlvisible. Final parts of larger specimens sometimesshow weak enrolment, but never become uniserialand flaring, and always remain in contact with theolder whorl. The test cross section is almost stronglenticular, enabling differentiation from the closelyrelated species P. planatus. Apertures of young,smaller individuals consist of an arrangement of cir-cular openings and become dendritic in the final testpart. Imperforate, porcelaineous walls surfaces are


covered with microscopical grooves (‘pits’) provid-ing light penetration through the walls. The grooves’arrangement in parallel series gives the impressionof ‘striae’.

Test size as indicated by the largest diameter isthe smallest of all investigated species. Frequenciesare significantly lognormal distributed with a meanof 523 µm and standard deviation of 138 µm. Pop-ulations of Peneroplis antillarum at different depthsconfirm the superposition of homogeneous frequencydistributions by showing discontinuities in distribu-tion form. Decomposition of the summary distribu-tion (e.g., Medgyessy, 1977) including all popula-tions from various depths at both transects yieldedin two normal distributions. One subpopulation con-sisting of smaller individuals is characterized by amean of 470 µm and standard deviation of 84 µm.Distribution parameters of the other subpopulationare 730 µm for the mean, with a standard devia-tion of 98 µm. The 79% to 21% ratio between bothsubpopulations results in a strong right-side skeweddistribution form.

Size distributions at various depths show a signif-icant increase in mean size correlated to depth whichis confirmed by parametric (product–moment cor-relation) and nonparametric (Kendall’s − ) statisticalanalyses. This trend is caused by ratio differences be-tween the two subpopulations correlated with depth.Comparison of decomposed depth populations us-ing one-way analysis of variance demonstrates sizestability for both subpopulations despite increasingdepth. While the subpopulation with smaller-sizedindividuals dominates in the uppermost 5 m (93%),its proportion decreases to 64% at 20 m. Althoughindividual numbers are low at 30 m, an estimatedratio of 1:2 confirms the shift towards larger sizedforms (66%). No size differences between both tran-sects were detected by statistical analyses (Kruskal-Wallis Test), either for the different depth popula-tions or the total population.

Ordering the four frequency distributions basedon the sum of ‘contour area’ shows that Peneroplisantillarum clearly prefers firm bottoms. Neverthe-less, only firm substrates of the northern transect arecharacterized by a significantly higher settlement.The remaining frequency distributions have simi-lar abundance, with identical frequencies on sandybottoms in the northern and firm substrates in the

southern transect. While abundance differences cor-respond to substrate type, distribution forms are sim-ilar within and differ between the transects. In thenorthern transect highest abundance occurs on bothsubstrate types at the shallowest depth, followed bya strong decrease to the deeper parts. Both substratetypes of the southern transect also demonstrate sig-nificant homogeneity in distribution form, with adecrease by depth and a maximum at 20 m.

Peneroplis planatus (Fichtel and Moll) (Fig. 8)

The test form of this species is similar to itsclose relative P. antillarum, both being distinguishedby involute tests where ‘striae’ densely cover theporcelaineous surface. The final, more weakly en-rolled part sometimes becomes rectilinear uniserial,but also keeps contact to the older whorls resulting inflaring chambers. A long row of regular apertures arecharacteristic for this final part. The strongest mor-phological difference to the related species consistsin the flat cross section.

The frequency distribution of largest test diameter(all samples) shows 2 distinct modes separated bydiscontinuity. This clearly indicates a superpositionof two subpopulations. Best results in fitting theo-retical distributions are achieved by a decompositioninto two lognormal distributions. In that case, right-side skewness of subpopulations can be interpretedas being due to the exponential growth based onthe logarithmic spiral, which is the characteristic testform of P. planatus. The first subpopulation, consist-ing of smaller specimens is distinguished by a meanof 577 µm (SD D 231 µm). The standard deviationis smaller (154 µm) for the second subpopulation,combined with a mean of 953 µm. Proportions ofboth subpopulations are rather similar, with a some-what higher amount (54%) in the first subpopulation.

Undecomposed samples at various depths con-firm the significant correlation with depth shownby statistical analyses (Kendall’s − ), but in contrastto the related species P. antillarum, the decrease inmean size becomes significant. This is again causedby varying proportions of subpopulations along thedepth gradient. Decomposition of these depth-depen-dent populations demonstrates constancy in distribu-tion parameters. The proportion of the first subpop-ulation increases constantly, starting with 35% nearthe surface, attaining 42% at 10 m and 64% at 20 m


Fig. 8. Test size distribution (A) and habitat (B and C) of Peneroplis planatus (Fichtel and Moll). Explanation see Fig. 7.

depth. A few specimen from 30 and 40 m again en-able estimation of proportion, confirming the depthrelated increase (70%) for the first subpopulationdistinguished by smaller test size. Both transects donot differ in test size either as a whole or regardingvarious depth populations (Kruskal-Wallis test).

Peneroplis planatus clearly prefers firm substrates;this is confirmed by ordering substrate types of tran-sects according to total frequencies. Highest abun-dance can be detected on firm substrates of both thenorthern and southern transect. P. planatus obviouslyavoids sandy substrates. Despite these clear differ-ences in total abundance between substrate types, theforms of depth distributions are quite similar, ex-cept for sandy bottoms of the northern transect. Inall three correlated distributions the optimum is lo-cated at 20 m depth, followed by a continuous and

rapid decrease. At 40 m, individuals only inhabit firmsubstrates of the northern transect, where they areabundant. P. planatus is rare at 30 m; this species istherefore restricted to the uppermost reef slope, butavoids reef flat areas, where it is extremely rare com-pared with its sister species P. antillarum.

Peneroplis pertusus (Forskal) (Fig. 9)

This species can easily be differentiated fromboth P. antillarum and P. planatus by an evoluteplanispiral enrolment combined with a pronouncedumbilicus in the initial test part. Furthermore, testsutures are significantly depressed and the rectilinearfinal part of larger individuals never shows flaringchambers.

Overall, test size is the same as in Peneroplisplanatus, but deviations from either normal or log-


Fig. 9. Test size distribution (A) and habitat (B and C) of Peneroplis pertusus (Forskal). Explanation see Fig. 7.

normal distributions are significant. This again isan argument for composed distributions. In contrastto P. planatus, populations taken at various depthsdemonstrate no clear differentiation into subpopu-lations. Only samples from 30 m depth (highestabundance) indicate bimodality. Trends in test sizecorrelated to depth, as pictured in P. antillarum andP. planatus, cannot be confirmed for P. pertusususing parametric (product moment correlation coef-ficients) and nonparametric tests (Kendall’s − ). Theproportions of both subpopulations therefore remainconstant with depth. The subpopulation with smallertest sizes (mean D 632 µm, SD D 139 µm) differs

from the second subpopulation (mean D 955 µm,SD D 100 µm). Proportions between subpopulationsremain rather constant at different depth, varyingbetween 61 and 69% in the first subpopulation andbetween 17 and 36% in the second. P. pertusus is theonly representative of the genus in the investigationarea in which a third subpopulation characterizedby much larger tests could be detected. Its lognor-mal distribution is distinguished by a mean of 1386µm and a standard deviation of 98 µm. While bothsmaller subpopulations demonstrate a strong over-lap, the third one is clearly separated. Although itsproportion is small (3 to 14%), no significant corre-


lation with depth exists: both 5 m and 40 m show thehighest proportion (14%).

One-way analyses of variance confirm differencesin total test size between the transects. Especially at10 and 30 m significantly larger tests can be found inthe southern transect.

An additional sample from 50 m depth was takenclose to the Nakanose reef after the tropical storms. Itcontained numerous specimens of P. pertusus, whichwas never detected at this depth in the main inves-tigation area. Test sizes differ from the samples ofthe main transects in so far as the first subpopulationdominates with a proportion of 86%. All remainingspecimens (14%) belong to the second subpopula-tion, and the third subpopulation is not represented.Significant differences to the larger test sizes in thesouthern transect may be caused by this distributionform.

Peneroplis pertusus demonstrates no clear pref-erences for particular substrates. While depth dis-tributions in the northern transect indicate a strongpreference for firm substrates, as confirmed by theranking of total abundance, frequencies in the south-ern transect do not differ significantly between sand,coral rubble or macroids. The distribution form issimilar in all transects; only sandy bottoms of thenorthern transect (with lower frequencies) show sig-nificant deviations. Especially the distribution onfirm substrates of the northern transect demonstratesthe transition to reef flat areas, where P. pertusus isabundant on the crest and reef moat close to the reeffront. Such clear transitions are absent in the south-ern transect, but abundance strongly increases withdepth, peaking between 10 and 30 m. Abundancegradually decreases to zero at 50 m.

Dendritina ambigua (Fichtel and Moll) (Fig. 10)

This species is similar in test form to Peneroplispertusus, but differs from the relative by the stronginvolute enrolment. Final rectilinear parts consistingof a few chambers are rare. Depressed chamber su-tures cannot be observed and striae based on groovesinstead of pit rows are less pronounced than in Pen-eroplis arietinus (Batsch), which in all other testcharacters is similar to D. ambigua. Apertures re-main dendritic during ontogeny and never becomea series of multiple openings typical for the genusPeneroplis.

The frequency distribution of test size is stronglyright-side skewed and cannot be fitted by theoreticalnormal or lognormal distributions. Correlation withdepth is significant as tested by parametric and non-parametric statistics. This leads to the assumptionthat populations are composed of two or more sub-populations with different distribution parameters,and that the obvious depth-related trend in test sizeis caused by proportion changes. Decomposition ofthe total sample into lognormal distributions yieldedtwo subpopulations. The group with smaller testsis characterized by an average test size of 556 µm(SD D 110 µm), while the corresponding valuesfor the second subpopulation are 1135 and 208 µm.Decomposition of the populations at 20 and 30 malso resulted in these two subpopulations. Their dis-tribution parameters coincide with the parameters ofthe total population, but proportions differ signifi-cantly between both depths. While in 20 m (216individuals) members of the small test group domi-nate (86%), individuals with larger test become morenumerous (54%) in the smaller samples (43 individu-als) from 30 m. This explains the significant positivecorrelation between test size and depth.

Based on total frequencies, D. ambigua preferssandy bottoms. It is absent on firm substrates inthe southern transect. Few specimens can be found at10 m on coral rubble of the northern transect. Despitethe preference for sand, abundance on this substrateis significantly higher in the northern than in thesouthern transect. Depth distributions are similarin form between sandy bottoms of both transects.Generally, few specimens can be found at 10 m,followed by a maximum at 20 m. After a rapiddecrease in numbers at 30 m, this species is absent indeeper parts of the transects.

Dendritina zhengae Ujiie (Fig. 11)

The planispirally coiled, involute tests are charac-terized by an umbilicus; the overlap by the last whorlis thus not as complete as in P. antillarum. Rectilinearfinal test parts consisting of 2 chambers at least arecommon, and these chambers do not touch the lastwhorl. Tests are flat, with sharp contours similar toa keel. This leads to pronounced elliptical cross sec-tions in rectilinearly arranged chambers. The smoothsurface is covered by single pit rows. Since these rowsare not deepened, striate ornamentation is lacking.


Fig. 10. Test size distribution (A) and habitat (B and C) of Dendritina ambigua (Fichtel and Moll). Explanation see Fig. 7.

The multiple aperture remains dendritic during on-togeny. Considering chamber arrangement and aper-tures, this species is similar to Peneroplis pertusus.

Similarities to P. pertusus also exist in test size.The frequency distribution of the total sample of D.zhengae shows significant deviations from normaldistribution, but can be fitted by lognormal distribu-tions. This significant fit may reflect the low spec-imen number, where strong deviations become lessimportant in inference statistics through the fewerdegrees of freedom. Test size and depth do not cor-relate. Decomposition of the frequency distributioninto lognormal distributed groups yielded 3 subpop-ulations. This is again similar to P. pertusus, as arethe distribution parameters. The first subpopulationis distinguished by an average test size of 506 µmand a standard deviation of 73 µm (second sub-

population: mean D 736 µm, SD D 87 µm). Thesubpopulation with largest tests is characterized bya mean of 1212 µm and a standard deviation of178 µm. Compared with P. pertusus, all parametersin every D. zhengae subpopulation (except of thestandard deviation of the third subpopulation) aresmaller than the related form. Proportions amongthe three subpopulations are similar, but differ inregard to depth. Decomposition of samples by depthyielded also three subpopulations, with insignificantvariation of the distribution parameters, but differentproportions. While at 20 m the first subpopulationshows proportion of 46% against 29% for the secondand 24% for the third subpopulation, samples from30 m are characterized by a clearer differentiationof subpopulations: 28% for the first; 38% for thesecond; and 34% for the third group.


Fig. 11. Test size distribution (A) and habitat (B and C) of Dendritina zhengae Ujiie. Explanation see Fig. 7.

Depth distributions according to transect and sub-strate type show a clear preference for sands in bothareas. This species is absent on firm substrates inthe southern transect. The northern transect is distin-guished by more specimens. Abundance differencesare significant between all substrates. The form ofthe depth distributions is simple, since most individ-uals are concentrated at 20 m and avoid shallowerparts of the fore reef slope. At 30 m in the northerntransect, only sandy sediments are settled by thisspecies and specimens can be sporadically found at40 and 50 m.

Dendritina cf. D. zhengae Ujiie (Fig. 12)

Based on the ecological species concept, this formseems to be a morphotype of Dendritina zhengae.Surface and apertures are the same as in the main

species; only test form differs. Strong lenticular,involute, and thick tests lack an umbilicus, and recti-linear final parts are not developed. Thus this form issimilar to Dendritina ambigua, differing only in testsurface and ornamentation.

Sizes are also similar to D. ambigua, showingthe same strong right-skewed frequency distributionwhich cannot be fitted by either normal or lognormaldistributions. Decomposition into lognormal distri-butions resulted in 2 perfectly fitted subpopulations,one characterized by a mean of 623 µm (SD D 134µm), and the other by a mean of 1377 µm (SDD 155 µm). A significant correlation of test sizewith depth could be caused by a proportion shiftof these two subpopulations in favor of the largertests. Proportions of the total sample are 91% forthe first and 9% for the second group. Decomposi-


Fig. 12. Test size distribution (A) and habitat (B and C) of Dendritina cf. D. zhengae Ujiie. Explanation see Fig. 7.

tion of populations from 20 and 30 m, where thisform is most abundant, yielded similar proportionsto the total population, that is, a content of 93% at20 m and 95% at 30 m for the first subpopulation.The significant depth-dependent trend resulted froma few (4) specimens living at 50 m in the northerntransect, all distinguished by large tests exceeding 1mm (meanD 1258 µm, SDD 190 µm as parametersof the lognormal distribution).

An additional sample from 50 m (taken east of theNakanose reef after the tropical cyclones) containeda large number (114) of D. cf. D. zhengae. Thefrequency distribution of test size is quite differentfrom the main transect. Again, a decomposition intolognormal distributions resulted in 2 subpopulations.While the distribution parameters of the first group

are similar to the main transect (meanD 712 µm, SDD 93 µm), the second subpopulation differs in theposition of the mean (1034 µm). Additionally, pro-portions are dissimilar to the main transect, showinga dominance (73%) of the larger-sized group.

The depth distributions of this form are extremelysimilar to the flat D. zhengae, but dominance onsandy bottoms of the northern transect is more pro-nounced. Few specimens were detected on firm sub-strates on the northern region, while this group isvirtually absent in the southern transect. On sandybottoms of the northern transect the distribution formis quite similar to the flat D. zhengae: few individ-uals on shallower areas of the slope (0 to 10 m), amaximum at 20 m, followed by a strong decrease.Some specimens were detected in the same transect


at 50 m, which is again in full agreement to D.zhengae. These correspondences indicate identity ofecological niches, a main argument for regarding D.cf. D. zhengae only as a morphotype of the samespecies.

6.2. Alveolinidae

This family of larger foraminifers belongs to thesuborder Miliolina according to their porcelaineouswall structure. Test enrolment is planispiral exceptthe initial coiling. Elongation along the coiling axisleads to fusiform test, which resists hydrodynamicand mechanical destruction by sediment transport.Further advantage of fusiform tests can be found inthe surface per volume ratio, which is much betterthan in biconvex tests of the Peneroplidae; thus sym-biotic algae are enriched in the last whorl gettingenough light for photosynthesis (Leutenegger, 1984).Both advantages, mechanical strength and large sur-face in relation to volume enable the construction oftests more than 2 mm in size. Only one species canbe found in the investigation area. The Alveolinidaeis the single family of the Miliolina that houses di-atoms as symbionts. These algae are common in allhyaline representatives of larger foraminifera.

Alveolinella quoyi (d’Orbigny) (Fig. 13)

Chambers of large, fusiform tests are dividedalong the coiling axis by septulae which results ina large number of chamberlets. They can be addi-tionally divided by horizontal plates, especially inthe last chambers. Since all chamberlets of succes-sive chambers are connected by openings, the finalchambers show a multiple row of apertures, whichbecome more abundant at the vertices of the spindle-like tests. Grooves covering the surface enable lightpenetration through the opaque tests.

Test sizes show a broad range, demonstrating sig-nificant deviations from lognormal and normal distri-butions. Depth-dependent correlation is not evident,and differences in test size between both transectsare also insignificant. Decomposition of all indi-viduals into lognormal distributed subpopulationsyielded two distinct groups. Distribution parametersof the strongly right-side skewed subpopulation withsmaller test sizes are 1109 µm for the mean and 892µm for the standard deviation. The second group is

characterized by a mean of 4225 µm and a standarddeviation of 698 µm. A single specimen from 40 mthat is more than 8 mm in length can be regarded asan outlier. It may be the only representative of a thirdsubpopulation with a 1% proportion of the total sum.The second group (larger tests) is more abundant(64%). Decomposition at various depths confirmedthe parameters of the total sample, but again showdifferences in proportions. Specimens from 30 and40 m reflect the total sample, e.g. demonstrate iden-tical proportions, but in the shallower parts (10 and20 m) the second subpopulation attains at least 87%,and the first group cannot be fitted by lognormal dis-tribution. The 50 m sample from the Nakanose reefagain deviates from the distribution of both transectsin so far as smaller individuals dominate with 94%.

Relations to substrates are quite similar to thoseshown for Peneroplis pertusus. A preference for firmsubstrates was obvious only in the northern transect,where specimens are most abundant on coral rubble.The opposite trend was found in the southern transect:specimens are significantly more abundant on sandthan on firm substrates (Wilcoxon paired-group test),but frequencies are lower. Depth distributions relatedto substrates are heterogeneous. A. quoyi avoids thereef edge, but its distribution on firm substrates alongthe northern transect is distinguished by a maximumat 10 m. After a strong decrease, frequencies remainconstant from 20 to 40 m. No specimens were foundat 50 m. All remaining three substrates are similarin distribution form. In the southern transect, the ab-sence of individuals at 10 m contrasts to the distinctoptimum on firm substrates of the northern transect.Maxima on all remaining substrates occurred at 30 m.Only a few specimens inhabit sandy bottoms at 50 mdepth (northern transect).

6.3. Soritidae

The third family of larger foraminifers belongingto the Miliolina is distinguished by large, circular,flat and platelike tests. After an initial planispi-rally coiled part, which can be reduced to only twochambers, all succeeding chambers are arranged ina circular manner surrounding the older test part.They are divided by septula into numerous chamber-lets which show different connections between andwith chamberlets of the succeeding growth stage.


Fig. 13. Test size distribution (A) and habitat (B and C) of Alveolinella quoyi (d’Orbigny). Explanation see Fig. 7.

Since chambers do not overlap, these connectionsand apertures are only found at the periphery. Porce-laineous walls of chamberlets become very thin onlateral sides. Such ‘windows’ allow light and car-bon dioxide penetration for symbiotic algae (Hansenand Dalberg, 1979). Most of the Soritidae housezooxanthellae (Leutenegger, 1977a, 1984; Lee andAnderson, 1991), but some use green algae as sym-bionts (Hallock and Peebles, 1993).

Parasorites orbitolitoides (Hofker) (Fig. 14)

Tests are flat, perfectly circular and rather smooth.Initial parts consisting of many chambers are always

planispirally coiled. The following rectilinear cham-bers become flaring in younger tests parts, leading tofinal circular chambers. Flaring and circular cham-bers are subdivided into ‘chamberlets’ by simple,ring-like septula (Gudmundsson, 1994). Surface de-pressions are pronounced at chamber sutures andweaker at septula of the chamberlets. Multiple aper-tures are arranged in a single row at the test periph-ery. The simple structure of septula in combinationwith the housing of green algae (Hallock and Pee-bles, 1993), which is typical for all members of theArchaiasinae, justifies an assignment of Parasoritesto this subfamily.


Fig. 14. Test size distribution (A) and habitat (B and C) of Parasorites orbitolitoides (Hofker). Explanation see Fig. 7.

Test size distribution is strongly right-side skewedand can be fitted by theoretical lognormal distribu-tions. A few large-sized outliers mark the existenceof a distinct subpopulation. Nevertheless, the distri-bution form of all investigated specimens does not fitoptimally to the lognormal distribution, and the his-tograms indicate an additional peak on the weaklydecreasing right distribution shoulder. Depth correla-tion is also significant. This again argues for a pro-portional shift of subpopulations in favor of groupswith larger tests. Decomposition into lognormal dis-tributed groups resulted in two subpopulations (first

group: mean D 809 µm, SD D 221 µm; second sub-group: mean D 1371 µm, SD D 271 µm). The firstgroup is dominant (71%), while the second subpop-ulation attains a value of 26%. The remaining 3%belongs to tests larger than 3 mm. Decomposition ofpopulations from different depths, starting with 20 mdown to 50 m, resulted in very similar distributionparameters for both subpopulations, but a shift in pro-portions was again significant. While proportions ofthe first subpopulation, starting with 80% at 20 m, de-crease in an almost linear manner (74% at 30 m, 66%at 40 m, and 54% at 50 m), the second group shows


an opposite trend (17% at 20 m, 22% at 30 m, 31% at40 m, and 36% at 50 m). Also, the proportions of verylarge tests increase from 3% at 20 m to 10% at 50 m.

The test size distribution at the Nakanose reef(50 m, two months after the main sampling period)differs again. The distribution form is much closerto a normal than to a lognormal distribution. Thisindicates that individuals are on average larger here.Decomposition into lognormal distributions resultedin an optimal fit by two subpopulations (mean1 D1206 µm, SD1 D 239 µm; mean2 D 1977 µm,SD2 D 356 µm). Individuals of the second subpop-ulation are more abundant (79%) than the smaller-sized specimens (31%). Members of a third subgroupcould not be detected.

Parasorites orbitolitoides obviously prefers sandysubstrates, as indicated by the total frequencies inthe various substrate types. Differences between firmand soft substrates are more evident in the north-ern transect. Frequencies significantly differ betweensubstrates and transects in distribution form.P. or-bitolitoides avoids the first 15 m. A distinct max-imum at 20 m characterizes distributions on bothsubstrates of the northern transect. The strong de-crease from 20 to 30 m weakens down to 50 m. Thisdepth is not indicating the lower distribution limit,since living individuals were dredged from 80 m.The distribution form in the southern transect is dis-tinguished by a weak increase starting at 20 m and amaximum at 40 m. Living individuals were found indredged samples from 70 m.

Sorites orbiculus (Forskal) (Fig. 15)

The initial test part is evolute and planispirallycoiled. Two large chambers form the embryonalapparatus in the more common megalospheric gen-eration. The planispiral test portion is as short asthe following part, consisting of flabelliform cham-bers. Annular chambers constructing the main testsurround the older test parts in an evolute matter.All chambers are subdivided into chamberlets byshort septula bearing connections to chamberlets ofthe same and the succeeding chamber (Gudmunds-son, 1994). A single row of apertures indicating theposition of septula is located at the test periphery.Restrictions of the chamber and chamberlet suturesat the lateral test sides result in strong waveformedchamberlets, which is typical for S. orbiculus. Most

specimens live permanently fixed to firm substrates,thus copying the substrate surface by test formduring growth. This species houses dinoflagellatesas symbionts, which seems to be characteristic formembers of the subfamily Soritinae.

Test size distribution is very similar at all depthsand can be fitted by single lognormal distributions.Extremely rare outliers with sizes larger than 3 mmwere found at each depth (<0.5%). Distributionparameters of the smaller-sized individuals are 1175µm for the mean and 477 µm for the standarddeviation. These parameters remain constant downto 30 m; only the sample from 40 m, which containsfew specimens, differs (meanD 1283 µm, SDD 543µm). Despite this anomaly, correlation with depthis insignificant, as no size differences between thetransects could be demonstrated.

Sorites orbiculus prefers firm substrates, as is re-flected in the order of total frequencies. Substratepreferences are more evident in the northern tran-sect, where differences between substrate types areextreme. Living specimens on sandy bottoms are alsorare in the southern transect, but exceed the abun-dance on the same substrate type in the north. Depthdistributions are homogeneous except for sandy bot-toms of the northern transect, where specimens arevery rare, and can be described as follows: Few spec-imens living at the reef edge mark the transition tothe reef flat, where S. orbiculus inhabits firm sub-strates. The abundance maximum is located on theslope between 10 and 30 m. After a strong decreasedown to 40 m, individuals become extremely rare inthe northern transect at 50 m.

Amphisorus hemprichii Ehrenberg (Fig. 16)

A large embryonic apparatus consisting of twochambers is succeeded by a series of few evoluteflabelliform chambers. Circular and annular cham-bers, which are divided by septula into chamberlets,construct the main test part. The alternative arrange-ment of septula with openings to chamberlets ofthe succeeding chambers results in a double row ofapertures at the test periphery (Gudmundsson, 1994).Tests are thicker than in S. orbiculus, and a medianlayer of additional apertures can be found in largetests; this points to relations with Marginopora ku-dakajimaensis Gudmundsson, either genetically orecologically. Tests are almost biplanar, despite the


Fig. 15. Test size distribution (A) and habitat (B and C) of Sorites orbiculus (Forskal). Explanation see Fig. 7.

possibility of fixing to firm substrates. Dinoflagellatesymbionts (Leutenegger, 1977a) confirm the positionto the subfamily Soritinae.

Test sizes show a broad range and clear differen-tiation into two subpopulations. The population withnumerous small-sized individuals is homogeneousand can be significantly fitted by lognormal distri-butions (mean D 601 µm, SD D 206 µm). Its pro-portion of the total fauna is 92%. Much larger-sizedtests are characterized by the mean of 5.413 mm andstandard deviation of 1.606 mm of a lognormal dis-tribution. The largest individual measures 8.67 mm.

The proportions of these second subpopulations arerather constant at all depths with a mean of 8%.Thus, they do not influence the significant positivedepth correlations of the test size. Since this trend isnot caused by a proportion shift in subpopulations,changes in distribution parameters corresponding todepth must be responsible. While the means of allpopulations tends to shift to larger values with in-creasing depth, the change in the standard deviationsis more obvious. They start with 194 µm at 10 mand gradually increase to 197 µm at 20 m, 218 µmat 30 m, and finally 275 µm at 40 m.


Fig. 16. Test size distribution (A) and habitat (B and C) of Amphisorus hemprichii Ehrenberg. Explanation see Fig. 7.

Test sizes from 50 m at the Nakanose reef differfrom the main transect. Nevertheless, the homoge-neous distribution is best fitted by a lognormal dis-tribution; the parameters are quite different. A meanof 1856 mm combined with a standard deviation

of 491 mm characterizes this distribution. No largerindividuals as members of the second subpopulationwere detected.

Additionally to depth correlation, differences be-tween the transects are also significant. Tests are


larger in the uppermost 10 m of the southern tran-sect, and they become significantly larger in deepersamples of the northern transect. These differencesmainly are caused by the much larger-sized sub-group, which prefers special substrates and depths.

A. hemprichii is the one of two species inwhich substrate preferences show differences be-tween ‘specimen number’ and ‘biomass’. Arrang-ing total frequencies according to specimen numberclearly demonstrates the preference for firm sub-strates, where differences in the northern transectare more evident than in the southern part. Firmsubstrates of the northern transect also show highestabundance by investigating biomass. The remain-ing substrates, however, do not differ significantly.These relationships are also reflected in the depthdistribution, which is more homogeneous regard-ing specimen number. A general trend can be de-scribed as follows: Transitions to high densities of A.hemprichii settling on the reef flat are marked by fewspecimens living at 5 m depth. As in S. orbiculus, thedepth distribution shows a maximum between 20 and30 m. The decrease at 40 m is also similar to its rel-ative, but the deepest living individuals were foundat 60 m. Depth distributions according to biomassdiffer on sandy bottoms in the southern transect in sofar as a maximum is located at the uppermost 10 m.This means that a few, but large individuals preferto live on this substrate. The opposite trend was de-tected in the northern transect. On both substratesthe biomass maximum is located in the deeper partsof the slope, despite the fact that the specimen dis-tribution also covers the uppermost slope in similarfrequencies. This explains the differences in test sizebetween both transects.

6.4. Amphisteginidae

This family of larger foraminifera belongs to thesuborder Rotaliina. A flat trochospiral arrangementof involute chambers leads to biconvex lenticulartests, where only the last whorl is visible from bothspiral and umbilical sides. Chambers are stronglyarched at the periphery, thus forming prolongations.Toothplates divide the chambers’ lumina and canbe recognized as stellate patterns on the umbilicalside. The wall of the each chamber totally coversolder test parts, and test thickening can be easily

achieved by this lamellar structure. Hyaline wallsenable light penetration that facilitates housing ofsymbiotic diatoms.

Amphistegina lobifera Larsen (Fig. 17)

Tests are thick and often globular, with the spiralside being more pronounced than the umbilical side.Lobate septa visible on both test sides of large adulttests are the main features of this species. Youngerindividuals do not show these strong lobes, makinga differentiation from the related species A. lessoniidifficult in very small specimens.

Test size distributions in A. lobifera are not assimple as in other species. Regarding all specimensas a single population, it cannot be fitted by eithernormal or lognormal distributions. Populations fromvarious depths can be fitted by theoretical distribu-tions, but they differ in form and parameters. Whilelognormal distribution is significant for the largepopulation from the reef edge (mean D 887 µm, SDD 274 µm) indicated by a strong right-sided skew-ness, the sample from 10 m with similar abundancecan be better fitted by a normal distribution (meanD 1249 µm, SD D 199 µm). Samples from 20 and30 m, with fewer individuals, are distinguished bysimilar distribution parameters of lognormal distri-butions (mean D 1100 µm, SD D 190 µm); theydiffer significantly from the lognormal distributedsample of the reef edge. Differences in test size be-tween both transects are insignificant, but positivecorrelations of size with depth exists (parametric andnonparametric tests). This points to a composition ofsubpopulations, which in the case A. lobifera seemsto be strongly overlapping. Decomposition into twolognormally distributed subgroups resulted in opti-mal fits for the total sample, the samples from thereef edge and from 10 m representing most individu-als. Therefore, sizes of A. lobifera can be describedas follows: smaller-sized individuals of the first sub-populations have a mean of 871 µm combined witha standard deviation of 155 µm (second subpopu-lation: mean D 1266 µm, SD D 153 µm). A fewspecimens with a test size of more than 2 mmare outliers and point to a third group. Proportionsof both subpopulations with abundant specimensclearly demonstrate a shift with depth. While thegroup with smaller tests decreases from 71% at thereef edge to 45% in 10 m and finally to 33% in


Fig. 17. Test size distribution (A) and habitat (B and C) of Amphistegina lobifera Larsen. Explanation see Fig. 7.

deeper samples, the second subpopulation shows theopposite trend, starting at the reef edge with 28%and attaining 66% in the deepest parts. The thirdsubpopulation never surpasses 2%.

Substrate preferences also remain unclear for A.lobifera. While in the northern transect this speciesseems to prefer firm substrates, abundance on sandin the southern transect is insignificantly higherthan on coral rubble. Except for low frequencieson sandy bottoms of the northern transect, the re-maining substrates do not differ significantly in fre-quencies. Depth distributions are on the other hand

more homogeneous. Deviations on firm substrates ofthe southern transect do not disturb the main trend,as proven by high correspondence in distributionform between the remaining substrates. A. lobifera ismost abundant at the reef edge, which demonstratestransitions to specimens living on the reef flat. Thedecrease is strong down to 20 m, and the deepestspecimens were found at 30 m.

Amphistegina lessonii d’Orbigny

Flat trochospiral tests are involute on both sides,resulting in biconvex forms, but axial sections are


not as rounded as in the related A. lobifera. Tran-sitions to the related species can also be found bydeveloping weak lobes on the normally straight septaof the spiral side, especially in specimens living inshallower areas. The angular shape in cross sectionsis caused by a rounded keel limiting the test periph-ery. One test side is pronounced in some specimens,but in contrast to A. lobifera the umbilical side be-comes thicker than the spiral side. Transitions frombiconvex to umbiliconvex tests are rare; thus, thetwo distinct morphotypes can easily be recognized.Since genealogical relations between both types areunknown, they will be treated in the following asdistinct groups in order to detect habitat preferences.

(a) Umbiliconvex form (Fig. 18)Test size distributions of the total sample and

populations taken from different depths are homo-geneous, strongly right-side skewed and can be op-timally fitted by a single lognormal distribution inevery case. Outliers with test sizes more than 1.3mm marking a second subgroup are rare and neverexceed 3%. The largest individual measured 2.72mm. Depth correlations of test size as well as sizedifferences between the transects are insignificant.Homogeneity of distributions and the lack of depthcorrelation prevent a decomposition into subgroupsbased on statistical methods. All distribution parame-ters from different depth populations remain constantand can be described by parameters of the summarydistribution with a mean of 700 µm and a standarddeviation of 173 µm.

The umbiliconvex forms of A. lessonii from 50 mdepth at the Nakanose reef differ neither in distri-bution form nor in parameters from the main tran-sects. Correspondence to the 50 m sample from thetransects was proven by parametric (t-test for un-equal variances) and nonparametric (Mann–WhitneyU -Test) tests.

Preferences for sandy substrate are evident in boththe northern transect and southern transect. Depth dis-tribution is less clear, as demonstrated by insignificantcorrespondence in distribution form between all tran-sects and substrates. Nevertheless, a summary trendcan be described. This morphotype is found at thereef edge only on firm substrates of the northern tran-sect. The maximum is located at 20 m. After a slowdecline to 40 m, the decrease down to 50 m depth

is rapid. This depth is the lower distribution limit inthe northern transect, but a few living specimens weredredged from 70 and 80 m in the southern transect.

(b) Biconvex form (Fig. 19)Test size distributions differ from the related mor-

photype in that they are more inhomogeneous andcannot be optimally fitted by single lognormal dis-tributions, especially in the shallower areas, wherebiconvex tests are extremely abundant. The fit issignificant only for the samples from the reef edge,from 40 m, and from the 50 m sample at Nakanosereef. Fitting all depth-related samples and the totalsample by single lognormal distributions resulted insimilar parameters for all distributions, which con-firms the insignificant depth correlation. Also, bothtransects do not differ in test sizes (mean D 631µm, SD D 193 µm). The few specimens larger than1.3 mm can be regarded as members of a secondsubgroup with proportions less than 5%. Its largestmember measures 2.11 mm.

Decomposition into lognormal distributions re-sults in optimal fits by two subgroups for the totalsample and the samples from 10, 20, and 30 m.The estimated mean for the first subgroup of a totalpopulation based on the proportions of the differentdepth samples is 547 µm (standard deviation D 140µm). The second subpopulations is distinguished bya common mean of 796 µm and a standard deviationof 114 µm. Proportions between these subgroups donot appear to be correlated with depth. While the firstsubpopulation reaches 47% at 10 m, the proportionrises to 60% at 20 m and sinks to 50% at 30 m, thusconfirming the insignificant depth correlation of testsizes.

Test size distribution from 50 m at Nakanosecompletely corresponds to the main trend and can besignificantly fitted by a single lognormal distribution.

This morphotype obviously prefers firm sub-strates as demonstrated by the order of total frequen-cies and tested by the Wilcoxon matched-pair grouptest. Abundance on firm substrates and frequencieson sand do not differ between both transects. Also,depth distributions are rather homogeneous and canbe characterized by the uninterrupted transition tothe reef flat especially in the northern transect. Thedistribution maximum is located between 20 and30 m followed by a decrease down to 50 m. This


Fig. 18. Test size distribution (A) and habitat (B and C) of Amphistegina lessonii d’Orbigny umbiliconvex form. Explanation see Fig. 7.

decrease continues to 90 m, which seems to be thelower distribution limit of this morphotype.

Amphistegina radiata (Fichtel and Moll) (Fig. 20)

The planispirally coiled involute tests are bicon-vex with a subangular periphery. Septal orientationis strictly radial near the center on both sides, butthey suddenly turn back after 2=3 of chamber height.Distance between septa is much smaller than in rep-resentatives of the A. lessonii group. Forms livingat the upper slope are thick and smooth on both

sides. Pustules become numerous with increasingdepth, starting on the umbilical side and coveringboth sides in all specimens from 50 m downwards.Transitions between both morphotypes are continu-ous, which prevents an objective differentiation intodistinct groups.

Test size distributions are bimodal in all samples.Since the parameters remain constant with increas-ing depth, the summary distribution is also bimodal(smaller-sized subgroup: meanD 855 µm, SDD 326µm; larger-sized subpopulation: mean D 1850 µm,


Fig. 19. Test size distribution (A) and habitat (B and C) of Amphistegina lessonii d’Orbigny biconvex form. Explanation see Fig. 7.

SD D 205 µm). Specimens exceeding 2.5 mm arenot fitted by either distributions and must be regardedas members of a third subgroup. The proportion ofthis group never exceeds 6% (mean D 2%) and nodepth correlation is evident. 3.7 mm is the largestsize of all investigated specimens. Depth dependen-

cies of the smaller-sized specimens are slightly sig-nificant, but both transects seem to be homogeneousin test sizes. This weak depth dependence is mainlycaused by the low number of the second subpopula-tion at 50 m (13%). Proportions remain constant (80to 20%) in all shallower samples.


Fig. 20. Test size distribution (A) and habitat (B and C) of Amphistegina radiata (Fichtel and Moll). Explanation see Fig. 7.

The Nakanose reef sample differs from the maintransects only in proportions of the three subgroups.Here the first subpopulation dominates (96.5%), andmembers of the second and third subgroup are rare(3 and 0.5%, respectively).

Amphistegina radiata prefers firm substrates asdemonstrated by the ranking of total abundance. Dif-ferences between transects are insignificant for firmsubstrates. This species is less abundant on sandybottoms of the southern transect and is extremelyrare on the same sediment in the northern area.

Depth distributions are homogeneous in the southerntransect and differ from the northern transect in theclear preference for deeper regions. A. radiata startson firm substrates in the north at 10 m, with an op-timum at 20 m followed by a strong decrease downto 50 m. This species is rare in the upper 20 m ofthe southern transect where it reaches a maximum at40 m. The decrease to deeper parts is weaker than inthe northern areas, and the deepest living individualswere dredged from 90 m.


Fig. 21. Test size distribution (A) and habitat (B and C) of Neorotalia calcar (d’Orbigny). Explanation see Fig. 7.

6.5. Calcarinidae

Representatives of this family are very abundantin the tropical and subtropical West Pacific. The flattrochospiral tests develop thick chamber walls andmuch test material is deposited at both lateral sides,creating globular tests. Additional chambers can befound there that leads to a three-dimensional cyclicchamber arrangement. Very strong spines almostarranged in the coiling plane give the appearanceof little stars or sun discs, the most characteristicfeature for this family. All calcarinids house diatomsas symbiotic algae.

Neorotalia calcar (d’Orbigny) (Fig. 21)

This species shows relationships to the Pararo-taliidae in its test structure, especially aperturalconstructions (Hottinger et al., 1991), but clearlybelongs to the Calcarinidae in respect to test andsurface structure and the development of spines ateach chamber, which are identical to spines of allother calcarinids. The last feature is highly variablein this species across its geographical distribution,ranging from an extreme weak development to very

long spines that makes the test similar to Calcarinadefrancii and complicates identification.

N. calcar is abundant on the reef flat, where itclings to small macroalgae, but only few specimensinhabit the uppermost reef slope. A single normaldistribution characterized by a mean of 941 µm (SDD 182 µm) optimally fits test size distribution. Thefit by a single lognormal distribution is insignificant,and further decomposition into subpopulations wasnot exercised. No correlation of size with depth wasdetected, but differences in test size between tran-sects were significant. The much fewer specimensfrom the southern transect are significantly largerthan individuals in the northern section (Kruskal-Wallis test).

Neorotalia calcar prefers firm substrates, and ismore abundant on coral rubble than on soft substratesin both transects. Areal preferences are also signif-icant. Specimens are more abundant in the northerntransect, as documented by the insignificantly higherfrequencies on sands in the northern compared withfirm substrates in the southern area. These pref-erences cannot be proven by the nonparametricalWilcoxon matched-pairs test, but is confirmed bycross-tabulation (Cramer’s V) with substrates and


Fig. 22. Test size distribution (A) and habitat (B and C) of Calcarina gaudichaudii (d’Orbigny). Explanation see Fig. 7.

depth acting as variables. Depth relations are simi-lar for all transects and substrates. N. calcar attainsmaximum abundance at the reef edge and stronglydecreases down to 20 m, where no living specimenwas found. Only 3 specimens were collected from30 m depth; they were obviously transported bycurrents to this depth.

Calcarina gaudichaudii (d’Orbigny) (Fig. 22)

This species is distinguished by large, flat trochos-piral tests with thick chamber walls that give rise tocircular contours. Only few but strong spines are reg-ularly ordered at distinct parts of the test periphery,resulting in a strong radial arrangement that remainsconstant during ontogeny. Spines become bifurcatedonly in agamonts, where additional smaller spinestotally cover the umbilical and spiral test surface in

adults. Both sides are covered in the megalosphericgeneration by tubercles. Their number, size, andheight show strong geographical variation that led tothe differentiation of C. spengleri (sensu Fichtel andMoll in Rogl and Hansen, 1984, not Hansen, 1981),a morphotype with pronounced tubercles.

Test size distribution is homogeneous for the totalsample and the sample from the reef edge. Since C.gaudichaudii prefers high energetic environments,both samples are similar in individual number. Thefew specimens living in deeper parts does not affectthe summary distribution. The latter can be signifi-cantly fitted by a normal distribution, while fitting bya lognormal distribution is insignificant. Parametervalues of the normal distribution are 1797 µm forthe mean and 588 µm for the standard deviation.No larger adult agamonts were found, so that the


proportion of this subgroup is probably less than 1%.The histograms based on more than 400 individualsof the total sample and from the reef edge clearlyshow two peaks; thus, a decomposition into normaland lognormal distributed subgroups was performed.While fitting by two lognormal distributions yieldedunsatisfactory results, decomposition into two nor-mally distributed subgroups was perfect (smallersized group: mean D 1318 µm, SD D 315 µm),larger sized subgroup: mean D 2086 µm, SD D 205µm). The proportion ratio is 38 and 61.5%.

Depth correlations are not significant for testsizes, but the few individuals from deeper parts havelarger tests (distribution parameters of the deepersamples: mean D 2711 µm, SD D 661 µm). Testsizes differ also between the areas. Parametric andnonparametric tests (Mann–Whitney U -Test) showthat the 8 individuals from the reef edge in thesouthern transect are significantly larger than the 400individuals from the northern transects.

Substrate preferences of C. gaudichaudii are simi-lar to N. calcar, as its frequency on firm substrates inthe northern transect is three times higher. Abundanceon sand in the northern transect is also significantlyhigher than on firm substrates in the southern transect,where only few specimens were found. No individu-als live on sands in the southern area. Depth distribu-tion is quite homogeneous between the transects andsubstrates, despite their different abundance. C. gau-dichaudii attains its frequency maximum at the reefedge, thus marking the transition to populations ofreef crest pools distinguished by extreme abundance.A strong decrease down to 20 m indicates the lowerdistribution limit at this depth.

Calcarina defrancii d’Orbigny (Fig. 23)

This species is intermediate in test form betweenNeorotalia calcar and Calcarina gaudichaudii. Testenrolment is similar to N. calcar; especially the lastchambers are identical between both species in struc-ture, surface, and apertures. Each chamber producesa long spine that does not merge into the chambersas in the related species. They are separated fromthe test, similar to spines in C. gaudichaudii. Rela-tions to the latter species exist in the development oftubercles on the spiral side. Spines of the larger ag-amonts are sometimes branched and numerous, butnever cover the spiral or umbilical test side.

Since this species is rare in the investigation areaand restricted to the uppermost slope, only test sizedistribution of all individuals could be significantlyfitted by a normal distribution (meanD 1372 µm, SDD 424 µm). Distribution parameters from depth pop-ulations differ slightly, with shallower individualsbeing distinguished by a larger mean. But this differ-ence is not expressed in significant depth correlation.Also, test size in both transects is homogeneous.

Substrate preferences are similar to both relatedspecies N. calcar and C. spengleri. C. defrancii sig-nificantly prefers firm substrates. In contrast to bothrelated species, abundance is higher on coral rubbleof the southern area than on sand of the northerntransect. Depth dependencies are homogeneous, ex-cept for firm substrates of the northern transect. Themaximum in the latter is located at 10 m followed bya strong decrease down to 30 m. All other substratetypes show their optimum between 20 and 30 m. Noliving specimens were found at 40 m.

Calcarina hispida Brady

Strong and large tubercles cover the thick, flat tro-chospirally coiled tests on both spiral and umbilicalsides. Test surface and spines are densely scatteredwith small spikes that are, in turn, structured by ultra-spikes. Spike length is negatively correlated to spinesize and two morphotypes can be differentiated bythis relation. Since transitional forms between bothtypes are rare and distribution areas do not overlap,they possibly indicate different species according tothe ecological species concept. Globular tests withshort spines and long spikes, which cannot grow inhigh energetic environments, are extremely abundantin deep reef moats, and were thus not found in theinvestigation area. Again, two morphotypes can beseparated in the less globular forms based on spinenumber, spine length, and transition into the test.The first morphotype is distinguished by long spinesthat are differentiated from the test as in C. defrancii.Spine number is lower than in the related species, butalways exceeds 6 in number. The other morphotypehas 4 to 5 short and thick spines that gradually mergeinto the test. This low spine number makes differ-entiation from Baculogypsinoides spinosus in youngindividuals difficult. Since genetic or genealogicalrelationships between both forms are unknown, they


Fig. 23. Test size distribution (A) and habitat (B and C) of Calcarina defrancii d’Orbigny. Explanation see Fig. 7.

will be treated separately as different morphotypesof a single species.

(a) Form defrancii (Fig. 24)Distribution of test size is extremely homoge-

neous for this morphotype, both in total specimennumber and populations from different depth. Alldistributions can be fitted by a single lognormaldistribution. Depth correlations are significant, e.g.values increase for both distribution parameters. Themeans continuously becomes larger starting from1125 µm at 20 m and attaining 1425 µm at 50 m.Standard deviations also demonstrate a similar lin-ear increase from 253 µm at 20 m to 375 µm at50 m. The coefficient of variation measuring linearchanges in both distribution parameters also changes,

increasing from 50.86 at 20 m to 136.16 at 50 m.These differences again hint at a superposition ofsubgroups with constant distribution parameters incombination with a proportion shift in correspon-dence to depth. Decomposition into two lognormallydistributed subpopulations yielded a better fit than aseparation by two normal distributed subgroups. Thedistribution parameters remain constant with depth(mean D 1098 µm, SD D 252 µm for the firstsubpopulation; mean D 1542 µm, SD D 298 µmfor the group with larger tests). No members of athird subgroup with extreme test sizes were found.The proportion of the smaller-sized subgroup shiftsfrom 80% at 20 m to 75% at 30 m and 40 m, andto finally 30% at 50 m. This explains the significantdepth correlation.


Fig. 24. Test size distribution (A) and habitat (B and C) of Calcarina hispida Brady form defrancii. Explanation see Fig. 7.

This morphotype prefers firm substrates, but likeother calcarinids it is more abundant in the northerntransect. Therefore, abundance on sandy bottom issignificantly higher in the northern part than on coralrubble and macroids in the southern transect. Despitethese abundance differences, depth distribution isquite similar on all substrates. This morphotype israre at the reef edge but becomes abundant at 20 mand attains its maximum at 30 m. The decrease isweak down to 50 m and the deepest specimens werefound at 70 m.

(b) Form spinosa (Fig. 25)The test size distribution of this morphotype is

quite different from the defrancii form in that the to-tal sample and depth populations show either strongright-side skewness or clear multimodal distribu-tions. Except for the sample from 5 m, no skeweddistributions can be fitted by a single lognormal dis-tribution. Thus a decomposition into 2 lognormallydistributed subpopulations is necessary and resultsin a significant fit of all skewed and multimodaldistributions. Depth correlation is again significant,but in contrast to the first morphotype, tests become


Fig. 25. Test size distribution (A) and habitat (B and C) of Calcarina hispida Brady form spinosa. Explanation see Fig. 7.

smaller with increasing depth. Distribution param-eters of the two subpopulations remain constant,again with exception of the shallowest sample fromthe reef edge. All other populations are characterizedby a mean of 1081 µm and a standard deviationof 293 µm for the first subgroup. These values arealmost identical to those of the first subgroup of

the defrancii form. The second subpopulation is dis-tinguished by a mean of 2068 µm and a standarddeviation of 478 µm, which is much higher than inthe first morphotype. Parameter differences betweenthe first and second subgroup cause inhomogeneitiesin all population distributions. Proportions betweenthe subpopulations change with depth, where the


Fig. 26. Test size distribution (A) and habitat (B and C) of Baculogypsinoides spinosus Yabe and Hanzawa. Explanation see Fig. 7.

first subgroup increases from 38% at 10 m to 56%at 20 m and then attains a constant proportion ofapproximately 75% from 30 to 50 m. The homoge-neous sample from the reef edge cannot be fitted bythese subpopulations (mean D 1427 µm, SD D 286µm).

The spinosa morphotype prefers firm bottoms andis extremely abundant on coral rubble and macroidsof the northern transect. It avoids sandy bottom ofthe southern area. Depth distribution differs from thedefrancii morphotype in the obvious preference forshallowest slope parts, but this form never occurs onthe reef flat. Numerous specimens inhabit the reefedge and the maximum is located at 10 m. After arapid decrease down to 40 m this morphotype is rarein deeper parts, but living forms with flat tests weredredged from 80 m.

Baculogypsinoides spinosus Yabe and Hanzawa(Fig. 26)

The initially trochospiral test becomes globular bythe addition of chamberlets on the spiral, umbilical,and lateral side. Three to four strong spines arearranged in a triangular to tetrahedral order andmerge into the test similar to the spinosa morphotypeof C. hispida. Similarities to this species also consistin large pustules located on the test surface and ina dense coverage by structured spikes. Apertures areonly visible in young specimens, while in adult testschannels that bundle in spines connect the cell withthe outside.

Test size distribution is inhomogeneous for thetotal sample and all depth populations, as is char-acteristic for the C. hispida form spinosa. The pop-


ulation from 20 m can be fitted by a lognormaldistribution, and the deepest populations are nor-mally distributed, but seem to be multimodal. Posi-tive depth correlation is significant. Size differencesare also evident between the transects, with largerindividuals inhabiting the southern area. Decomposi-tion into two lognormally distributed subpopulationsresulted in optimal fitting for the total sample andall depth populations, distinguished by rather iden-tical distribution parameters. The first subgroup ischaracterized by a mean of 1233 µm and a standarddeviation of 298 µm (second subpopulation: mean D2483 µm, SD D 604 µm). Proportions between thetwo subgroups changes with depth, starting with adominance of the smaller sized forms at 20 m (96%)and decrease to 79% at 30 m. Proportions become30% at 40 and 50 m, explaining the positive depthcorrelation in test size.

Baculogypsinoides spinosus is the only calcarinidspecies inhabiting the sandy bottoms at the Nakanosereef. Differences between both 50 m samples — onefrom the transects and the other from Nakanose —are insignificant (t-test for equal variances).

According to total abundance in the transects,this species prefers firm substrates. As opposed tothe other calcarinids, abundance on firm substratesdoes not significantly differ between the transects;the same holds for sandy bottoms. Depth relationsare similar for all substrate types as demonstrated byhomogeneous depth distributions. B. spinosus startswith few specimens at 10 m and gradually becomesmore abundant at 20 m. The maximum is locatedbetween 40 and 50 m, with the deepest individualsbeing dredged from 80 m.

Baculogypsina sphaerulata (Parker and Jones)(Fig. 27)

Tests of this species are the most advanced incalcarinids. The initial trochospiral chamber arrange-ment is reduced to a maximum of three chambers.Afterwards, chamberlets are added in a cyclic modeat each test side, but a larger number is positionedin the ‘horizontal plane’, where 4 to 9 spines aredeveloped. Therefore, tests are biconvex and not asglobular as in B. spinosus. Numerous small pustulescovering the surface mark the position of solid pil-lars that are inserted between the vertical rows ofchamberlets.

Baculogypsina sphaerulata seems to be restrictedto the intertidal zone, where it is extremely abundant.Only few living forms can be found in the uppermostsubtidal of the reef edge. Eight individuals werefound at 4 m in the northern transect, but an addi-tional sample taken at low tide in 1 m depth yielded55 specimens. This confirms the restriction of B.sphaerulata to the reef flat. Test size distribution wasstudied including the 1 m sample. This total samplecould be fitted by either normal or lognormal dis-tribution, whereby the fit using the latter theoreticaldistribution provided better results. The few tests onthe reef slope are distinguished by a mean of 1429µm and a standard deviation of 473 µm. Sizes ofthe few specimens from 5 m do not differ from theshallower sample (Mann-Whitney U -Test).

Substrate preferences could not be tested due tothe low number of individuals, but living specimenswere restricted to the northern transect. One indi-vidual that was possibly transported by currents intodeeper parts was detected on coral rubble at 30 m.

6.6. Nummulitidae

Planispiral evolute and involute large tests charac-terize this family. Chambers may be divided intochamberlets by septula, and a highly developedcomplex channel system enables direct connectionsbetween chambers of different whorls (Hottinger,1977b). Therefore, protoplasm can extrude from ev-ery point of the test margin to the outside andapertures become superfluous in some species. Allnummulitids harbor diatoms as symbiotic algae (e.g.,Lee and Anderson, 1991).

Operculina ammonoides (Gronovius) (Fig. 28)

Involute or slightly evolute planispirally tests aretypical for this species. Axial sections show roundedmargins and parallel lateral sides even in thick in-volute tests. The test surface is characterized inshallower-living forms by few pustules surround-ing a distinct central knob. These pustules start tocover septal parts of the test surface in deeper-living, slightly evolute specimens. Morphologicaltransitions can be found to the smooth form O.discoidalis (d’Orbigny), which is distinguished bynarrow chambers, rhomboedric axial sections lead-ing to a marginal keel, a large central knob, and the


Fig. 27. Test size distribution (A) and habitat (B and C) of Baculogypsina sphaerulata (Parker and Jones). Explanation see Fig. 7.

lack of pustules. This relative is extremely rare onfore reef slopes, but frequently inhabits fine-grainedbottoms of the lagoon behind patch reefs. Thus, itcould be recognized as a different species accord-ing to the ecological species concept. Morphologicaldifferences of O. ammonoides to the deeper-livinggenotype O. complanata (Defrance) are expressed inthicker, slightly involute tests and the lack of septalfolds (Hottinger, 1977b). The flat, large, and evolutetests of the genotype (Cushman, 1914) are denselycovered by pustules, which may act as light-collect-ing mechanisms in deeper (>50 m), light-depletedenvironments. Differences in test size and thicknessare also proven for O. ammonoides from the RedSea, but regarded as different phenotypes (Fermont,1977; Pecheux, 1995). Development of septal foldsthat characterizes O. complanata are not reported byPecheux (1995) despite X-ray investigations. Obvi-ous transitions of O. ammonoides to the genotype O.

complanata in morphological characters justify theposition of this species in Operculina.

Test sizes are inhomogeneous and cannot be fit-ted by a single normal or lognormal distribution.Decomposition into two lognormal frequency distri-butions results in optimal fit for the total sample andall depth-related populations. The parameters of bothsubpopulations remain unchanged with increasingdepth, as do proportions between both subgroups.Therefore, no depth correlation was induced by aproportion shift. The mean size of the first subgroupis 833 µm (SD D 302 µm). Proportions vary ran-domly between 33 and 44%. An average size of2008 µm (SD D 533 µm) characterizes the secondsubpopulation whose proportions lie between 56 and66%. The remaining few percentages consist of in-dividuals larger than 4 mm; they are members ofa third, large-sized group. A maximum test size of7.14 mm was reached by a specimen from 50 m.


Fig. 28. Test size distribution (A) and habitat (B and C) of Operculina ammonoides (Gronovius). Explanation see Fig. 7.

Size differences between the transects are only sig-nificant in the uppermost 20 m, where slightly largerindividuals live in the northern transect.

The test size distribution of O. ammonoides fromthe Nakanose reef differs insofar as the second sub-group is distinguished by significantly higher pa-rameter values. Mean test size (3045 µm) is largerthan that of the second subpopulation of the tran-sect, accompanied by a broader standard deviation(829 µm), while distribution parameters of the firstsubgroup are similar in both investigation areas.

Operculina ammonoides is abundant on sand inboth transects, but frequencies are similar on softbottoms and firm substrates along the northern tran-sect. Only macroids and coral rubble in the southerntransect are less inhabited by this species. Depthdistributions are homogeneous between substrates

and transects, despite minor deviation from the maintrend on firm substrates of the southern transect. Thisspecies avoids the reef edge and is rare in the up-permost 10 m of the slope. The maximum is locatedbetween 30 and 40 m, followed by a decrease downto 50 m, where O. complanata begins to replaceO. ammonoides and becomes extremely abundant onthe deeper slope. The lower distribution limit of O.ammonoides seems to be located at 60 m.

Nummulites venosus (Fichtel and Moll) (Fig. 29)

The thick planispirally coiled tests are involuteand lenticular in smaller individuals. Sigmoidal septabetween undivided and narrow chambers curve back-wards at the periphery, where a thick marginal chordis developed. Large-sized specimens become thinand flat in final whorls, but retain their involute


Fig. 29. Test size distribution (A) and habitat (B and C) of Nummulites venosus (Fichtel and Moll). Explanation see Fig. 7.

enrolment. The test surface is smooth and neverdevelops structures like pillars, knobs, or pustules.

Test size distributions of the total sample and fromdifferent depths cannot be fitted by single normal orlognormal distributions. Decomposition into lognor-mally distributed components resulted in optimal fitsby 3 subgroups. All subpopulation parameters re-main constant between different depths. The firstsubgroup is characterized by a mean of 1012 µmand a standard deviation of 348 µm (second sub-population: mean D 2002 µm, SD D 532 µm; thirdgroup: mean D 5441 µm, SD D 728 µm).

No depth dependence in test size was evident dueto the random proportions in samples from differ-

ent depths. While the second subgroup begins anddominates at 30 m, differentiation between the firstand second subgroup becomes pronounced at 40 and50 m, with a more or less constant ratio of 1.75 in fa-vor of the second subgroup. Proportions of the third,large-sized group are extremely high (26%) at 40 m,and remain important at 50 m both along the maintransects (4%) but also in the Nakanose reef (6%).Samples dredged from deeper waters confirm thetrend to high proportions of the third subgroup withincreasing depth. Its members become dominant at60 m (71%) and 70 m (77%).

Nummulites venosus is restricted to sandy bottomsin both transects, and differences in abundance are in-


Fig. 30. Test size distribution (A) and habitat (B and C) of Heterostegina depressa d’Orbigny. Explanation see Fig. 7.

significant. A few individuals were found on firm sub-strates at 50 m, where the most sediments are gravel.The depth distribution is homogeneous in both tran-sects. N. venosus avoids shallowest slope parts andstarts with extremely few specimens at 20 m, attainingmaximum abundance at 50 m. The deepest individu-

als were dredged from 80 m and a single specimenwas recorded at 90 m.

Heterostegina depressa d’Orbigny (Fig. 30)

Size and form is very similar to Nummulitesvenosus. Thick involute tests are characteristic for


smaller-sized individuals. The peripheral flatteningof involute chambers in the last whorls of large spec-imens is similar to the related species N. venosus.Main differences are in the division of chambers intochamberlets by septula, which helps resist mechan-ical stress. In contrast to the related genus Planos-tegina, which inhabits deeper environments and ischaracterized by evolute flat tests, H. depressa has acompletely smooth surface.

Test size distributions show significant fits bysingle normal distributions in samples from the reefedge and 10 m (mean D 1888 µm, SDD 699 m). Alldeeper samples fall into 3 subgroups distinguishedby lognormal distributions. Distribution parametersdo not significantly change between samples (firstsubgroup: mean D 795 µm, SD D 336 µm; secondsubpopulation: mean D 1922 µm, SD D 573 µm;third group: mean D 3945 µm, SD D 703 µm).The largest specimen measured 10.05 mm (at 30 m).Parameters of all three subgroups from the Nakanosesample reflect those of the deeper transect samples.

Significant positive depth correlations of test sizeare caused by the same factors as in N. venosus.While proportions between the first two subpopula-tions change randomly — ratios: 0.62 at 20 m, 1.51at 30 m, 3.65 at 40 m, 0.30 at 50 m, and 0.37 atNakanose — proportions of the third subpopulationincrease significantly. Down to 20 m the value is lessthan 1%, but suddenly increases to 15% at 30 and40 m. Samples from 50 m show the highest propor-tion (40%). The northern and southern transect donot differ in test size.

Substrate preferences are not as clear as in theother nummulitids. According to individual num-bers, H. depressa prefers firm substrates. Its frequen-cies in both transects are statistically identical. Softbottoms of the southern transect are inhabited in highfrequencies, although still lower than firm substrates.Few living specimens were found on sands of thenorthern transect. Biomass differs insofar as indi-viduals on sandy bottoms of the southern transectseem to have larger tests than forms living on hardsubstrates in the same area. Depth distributions aresimilar in all substrates where H. depressa is abun-dant; only sands along the northern transects showslight differences. This species is rare near the reefedge, but abundance suddenly increases at 10 m. Themaximum is located between 30 and 40 m, followed

by a slow decrease to 50 m (deepest H. depressa at80 m).

7. Discussion

Habitats of larger foraminifera are determined bya set of ecological gradients. The main factors in-fluencing the distribution of symbiont-bearing largerforaminifers are temperature, light intensity, watermovement, substrate, and food. The nutrient uptakeby the host seems to be important for the symbi-otic microalgae (Hallock, 1981), but intensive workis necessary to clarify this problem, especially in in-dividuals whose tests lack apertures (Lee et al., 1980,1991). Temperature affects distribution of larger for-aminifers in two ways. Depth limits may be causedby low temperatures, especially when a thermoclineis developed; geographical latitude in combinationwith ocean currents and their seasonal changes re-strict foraminiferal distribution by low temperatures.Since temperature is rather constant in the investiga-tion area and never drops below 19ºC at 50 m duringwinter months, the habitat investigation here couldbe restricted to the remaining factors ‘light inten-sity’, ‘water movement’, and ‘substrate type’. Table 4shows the adaptation of foraminiferal species to thesefactors in the investigation area using ordinal scales.All species demands are summarized below in outlineform according to their systematic position.

Peneroplis antillarum is adapted to high energeticenvironments and strong irradiance by attachmentto well-structured firm substrates in uppermost reefparts. Such habitats can be found on the reef crest,where abundant P. antillarum hide between filamen-tous macroalgae and in the small holes and groovescharacterizing the well-structured coral rubble in theuppermost northern slope (Hohenegger, 1994). Thisspecies also intensively inhabits reef crests in thesouthern part, but the less structured larger cob-bles of the uppermost slope in the southern transecthinder settlement due to the exposure to breakingwaves.

Whether the two clearly differentiated subpopula-tions in test size represent cohorts or generations hasto be answered in the future by studying populationdynamics or investigating reproduction, but the ob-vious high proportion of the second subgroup below


Table 4Adaptation to substrate (1) (A D northern transect only, B D southern transect only), light intensity (2), and water energy (3). Proportionsof subgroups in percentages (4). Explanation of depth correlation in test size (5) by either proportion shift with stable distributionparameters or growth (explanation see text)

the surf zone may indicate an increase in gamonts,while smaller-sized asexually reproducing schizontsdominate habitats with extreme water movement.

While Peneroplis antillarum is typical for the reefcrest, P. planatus is more abundant on the slope,but also prefers high irradiance. The distribution


maximum at 20 m depth indicates a preference formoderate water movement, avoiding extreme energyof breaking waves. The high number of living in-dividuals on sandy bottom in the southern transectcan be explained by erosion from larger substratecomponents with weakly structured surfaces throughwave action.

The significant bimodality in test size distributionmay represent different generations (gamonts andschizonts, Faber and Lee, 1993), but explanationby cohorts cannot be excluded. Further study ofpopulation dynamics may shed light on this problem.

The habitat of Peneroplis pertusus is similar to P.planatus but demonstrates broader ranges respondingecological gradients. Although this species is abun-dant on the reef crest, firm substrates of the slopewith well-developed surface structures are settled insimilar frequencies down to 40 m. High abundanceon sandy bottoms of the southern transect can beexplained by erosion through the greater hydrody-namic forces in this area versus the northern part.Small tests from sandy bottoms at 50 m depth eastof the Nakanose reef may be transported down thesteep slope by storm-induced currents. This opin-ion is strengthened by the fact that sampling wasconducted two months after the investigation of themain transect; during this interval two tropical cy-clones struck Okinawa.

The three modes in test size distributions areclearly explained by generation differences. Whilethe small subgroup with largest tests indicate aga-monts, determination of both subgroups with smallersizes remains unclear. Observation of reproductionor population dynamics may answer the questionif differences are based on cohorts or generationsin form of schizonts and gamonts. An argumentfor the latter hypothesis is the significant propor-tion increase with depth of the second subgroup(interpreted as gamonts). The population from theNakanose reef, taken 2 months after sampling in themain transects, differs in so far as the first subgroupwith smallest tests is well represented.

The strong lenticular test form of Dendritina am-bigua enables life on coarse-grained sediments thatare not extremely disturbed by high water energy.This may explain the predominance of D. ambiguaon sands in the more protected northern transect.Dependence on light seems to be important for this

species; it is therefore restricted to the uppermost30 m, but avoids the zone of breaking waves.

Bimodality in test size is more strongly expressedin deeper waters, but an interpretation as cohorts ordifferent generations is difficult.

Dendritina zhengae prefers well-illuminated areasdown to 40 m. Individuals live on sandy bottomsand avoid regions exposed to extreme hydrodynamicforces. This explains the higher abundance in moreprotected areas of the northern transect; the lowerfood availability in the southern area may also beresponsible for the limitation to 20 m in this region.

Test size distribution, with three distinct modes,is similar to P. pertusus and could be explained inan identical manner. The group with largest tests, in-terpreted as agamonts, is clearly separated from bothsubgroups with smaller tests. The second subgroupwith lower abundance at 20 m but higher numbersin the deeper parts may represent gamonts, while thefirst subgroup marks asexually produced schizonts.

Depth distributions of the lenticular Dendritinacf. D. zhengae are extremely similar to the flat form,but dominance on sandy bottoms of the northerntransect is more pronounced.

Although the ecological demands seem to be thesame as in D. zhengae, morphological differencesto the main species are augmented by varying testsize distributions. Large-sized tests are rare and con-centrated at deeper transect parts (50 m). Whileall transect samples can be decomposed into twosubgroups with identical distribution parameters andconstant proportions over all depths, the populationfrom the Nakanose reef (50 m) differs significantly.An explanation based on gamonts and schizonts hasthe same degree of probability as the interpretationthrough parameter shift by growth of the first sub-population, since the Nakanose sample was taken 2months after the main sampling period. Populationdynamics or reproduction studies may clarify thisproblem.

The distributions of Alveolinella quoyi confirmthe assumption that this species prefers well-illumi-nated firm and hard substrates with structured sur-faces providing shelter from extreme hydrodynamicforces. Individuals live in tiny grooves or holes andare normally fixed to the substrate by pseudopods ex-truding from one vertex. Pseudopods of the aperturalface and the free vertex are responsible for food gath-


ering beside their function in attachment (e.g., Lippsand Severin, 1986). The weakly structured compo-nent surfaces in the more exposed southern transectmay be responsible for the minor representation ofA. quoyi here and explains the relatively higher pro-portion of living specimens on sandy versus firmsubstrates. The significant decrease in abundancewith depth on firm substrates of the northern transectseems to be correlated with the increase in substratesmoothness, which allows erosion of living formsand explains low abundance on deeper sands.

A single individual with extreme test size can beinterpreted as an agamont, while the explanation forboth subgroups with smaller sizes remains difficultwithout population dynamic or reproduction studies.The second subgroup with larger tests, character-ized by higher proportions, can be interpreted asgamonts, leaving behind a smaller subgroup of sch-izonts. Small-sized tests with identical distributionparameters to this first subgroup were collected fromthe deep Nakanose reef station; this may be inter-preted on the one hand as transportation of schizontsdown to 50 m by tropical cyclones, although thevery few gamonts weaken this argument. This ex-planation is impeded by the extremely weak amountof gamonts. On the other hand, distributions can beexplained by cohorts, whereby the Nakanose sample(September) represents a situation after the main re-production phase (starting in June), whereas the Junesamples from the transect may represent a maturecohort state with starting reproduction.

The regular, flat and plate-like tests of Parasoritesorbitolitoides hinder fixation to well-structured firmsubstrates in order to escape hydrodynamic forcesin the surf zone. Thin walls and tests enable pen-etration of photons necessary to maintain algae indepths characterized by low light intensities despiteporcelaineous walls. Therefore this species shows thedeepest distribution range within the soritids. Whilesandy substrates in protected areas of the north-ern transect are intensively inhabited, settlement onsands starts in deeper regions of the southern tran-sect, avoiding sediment motion in high energy shal-low environments.

The few large-sized tests in the transects mayrepresent agamonts. The two subgroups obtained bydecomposition are difficult to explain. Following thetrimorphism hypothesis, the subgroup with small

tests and higher proportions in the shallower regionsmay be interpreted as schizonts. The larger gamontsare characterized by low proportions in shallowerand higher proportions in deeper parts. This cor-responds to the higher amount of giant agamontsresulting from sexual reproduction in depths below20 m. The Nakanose reef sample confirms this inter-pretation by growth of both generations in equivalentdegrees, where larger gamonts dominate populationsin 50 m owing to weak water movement that favorssexual reproduction.

Sorites orbiculus prefers highly illuminated re-gions on the reef crest and upper reef slope. Speci-mens do not seem to be affected by UV-irradiationsince they live on seagrass leaves or algal thalli thatare exposed to extreme sunlight in the shallow reefmoat. Intensive attachment through pseudopods tolarger components in the slope area characterizes S.orbiculus, where the surface is often copied in testform. This species is abundant on well-structuredlager components of the northern transect and alsofrequent on unstructured components in the southernarea. The many specimens found on sands in thesouthern part again could be explained by erosionthrough water movement, since fixation to less struc-tured components is weaker than to well structuredsurfaces.

The test size distributions hint to two generations,as are typical for members of the Soritinae. Large-sized tests representing agamonts are extremely rare(<0.5%). The homogeneous majority obviously re-produces asexually (Kloos and Mac Gillavry, 1978),with the breeding season probably being early sum-mer. Therefore, all large-sized schizonts disappear inJune, followed by fast test growth of broods duringsummer; this explains the average small tests of theinvestigated specimens. This hypothesis is confirmedby the small differences in mean test size betweenthe shallowest samples (10 to 20 m) from early Juneand the deepest samples taken in the first week ofJuly.

The habitat of A. hemprichii can be characterizedas highly illuminated regions in the uppermost slopearea and reef crest. Individuals strongly attach tofirm substrates, but never copy the surface by testform. Erosion by extreme water turbulence easilytransports specimens due to the high floating capac-ity of their flat tests. Only small specimens settle in


the northern transect on well structured components,while the smooth surfaces of cobbles in the deepernorthern transect and in all depths of the southernarea enable settlement of larger-sized individuals.The relatively high number of living A. hemprichiion sandy bottoms can again be explained by moreintensive erosion in the southern parts. In contrastto the related S. orbiculus, the larger and robustA. hemprichii seems to be more adapted to sandybottoms.

Size distribution can be explained by two genera-tions, where the proportion of large agamonts is rel-atively high (8%). The remaining homogeneous sub-group must be interpreted as asexually reproducingschizonts. The hypothesis of paratrimorphism wasintroduced by Leutenegger (1977b) for Amphisorusand Sorites, and studied in more detail by Zohary etal. (1980) using samples from the Red Sea. Popu-lation dynamics of the closely related Marginoporakudakajimaensis, which is abundant on reef crests inthe Ryukyus, confirms the extremely low numbersof agamonts on the crest and an annual asexual re-production of the megalospheric generation in June(Fujita, 1997). A second reproduction cycle starts inautumn, but all individuals disappear in June. Up to40% give rise to offspring of the next generation.Agamonts of A. hemprichii are more abundant onthe slope than on the crest; thus, gamonts — orschizonts that produce gametes and young schizonts(Kloos and Mac Gillavry, 1978) — must also be ex-pected in higher numbers compared to the reef crest.Homogeneity in test sizes prohibits differentiationbetween gamonts and schizonts, which may differin proloculus form or size. Further investigation onreproduction may enlighten this problem. The smallincrease in size from the reef edge down to 50 m canbe explained by growth, since sampling started inearly June in the shallowest areas and deepest partswere investigated one month later. Larger tests at50 m near the Nakanose reef reflect growth becausethis sample was taken 2 months after the last sam-pling in the transects. Exponential test growth maybe responsible for the large differences in distribu-tion parameters between the Nakanose sample andthe main transects.

Amphistegina lobifera definitely prefers the shal-lowest reef sections, inhabiting the crest in largenumbers. It avoids regions of extreme illumination

by hiding between thalli of macroalgae or livingin the shadow of larger components (Hohenegger,1994). The species resists high water energy throughpseudopods extruding from the structured apertures.This fixing mechanism enables settlement in tinygrooves and holes of components or rocks in theuppermost slope. Poorly structured components suchas those found in the southern transect, were notinhabited by A. lobifera, but this species becomesabundant in the deeper, quieter parts. The highertotal number of A. lobifera in the southern transectcan be explained by the lack of space competitionwith the calcarinids that dominate the northern areas.The large number of specimens living on sand in thesouthern transect could be explained by erosion, butA. lobifera seems to be adapted to strong sedimentmotion by its dome-shaped spiral test side.

The decomposition of subpopulations accordingto test size with varying parameter values impedesan interpretation as generation differences, but themany individuals with smaller tests at the reef edgeand decreasing proportion with depth supports theinterpretation as schizonts. Using this interpretation,the larger gamonts become abundant in deeper partswhich have more agamonts (2%) with sizes >2 mm.

The biconvex morphotype of Amphisteginalessonii inhabits the uppermost slope and settleson the crest in much lower numbers than A. lobifera,which dominates these highly illuminated regionswith extreme water movement. A. lessonii is moreabundant on firm substrates of the southern transectin correspondence to the lack of space competitionby calcarinids, but again the high abundance onsand here may be explained by erosion and rub-ble smoothness, which hinders strong fixation to thesubstrate. Test flattening seems to be correlated withdepth, facilitating light penetration through thin testwalls (Hallock and Hansen, 1979; Hallock et al.,1986).

The biological basis of the distinction into sub-groups according to different sizes is unclear anddifficult to explain. Trimorphism seems to be a com-mon reproductive strategy within the amphisteginids(Dettmering, 1997; Harney et al., 1998), especiallyin the shallowest slope parts where high water move-ment impedes copulation of gametes (Rottger et al.,1990a). This may explain the dominance of onehomogeneous group with small test sizes at the


reef edge, interpreted as schizonts, and the lack oflarger-sized agamonts. Deeper populations fall intotwo subgroups, whereby the group with larger testsmay represent gamonts. This interpretation is sup-ported by the small number of agamonts, especiallyin the deepest samples of the transects. Nevertheless,samples from 40 m and the Nakanose reef deviateinsofar as they show single lognormal distributionswith identical parameters to the reef edge population.

The strong umbiliconvex morphotype of A. les-sonii seems to be an adaptation to coarse-grainedsediments that are intensively moved by waves. Themechanical advantages of such tests against shearingforces are obvious (Wainwright et al., 1976; Wet-more and Plotnick, 1992).

While the few outliers with large tests may repre-sent agamonts, the homogeneous group with smallertest sizes cannot be differentiated into subgroups;thus, an interpretation as schizonts or gamonts isimpossible based only on test sizes. Constancy insize with increasing depth and comparison with theNakanose reef sample (identical parameter values) isan argument for a more or less continuous breedingand the lack of fixed reproduction seasons in thismorphotype.

Amphistegina radiata avoids high energetic envi-ronments and extreme irradiance; it is therefore ab-sent on the reef crest or in the moat. Substrate attach-ment seems to be weaker than in representatives ofthe Amphistegina lobifera=lessonii group, explainingthe minor abundance on firm substrates in the up-per southern transect. On the other hand, structuredsurfaces of reef rocks or larger components in thenorthern transect enable settlement in the upper sloperegions. The higher total abundance in the south-ern transect can again be explicated by the minimalspace competition with rare calcarinids. Settlementon sands in the southern area may be explained byerosion, but the weak flow velocity below 30 m doesnot support this interpretation. The strong biconvextests resist sediment motion; therefore, sands seemsto be also the natural habitat of A. radiata. This is re-flected in the depth range of this species (lower limit:90 m), where all sediments below 50 m are sands witha low proportion of gravel. Test flattening and the de-velopment of pustules covering the surface, whichfacilitates light penetration, starts at 30 m, but thiswas not quantitatively treated and tested.

Amphistegina radiata is the only member of theAmphisteginidae in which the clear distinction intosubgroups according to size remains constant, bothwith depth and with time. Samples from differentyears and seasons, for example, taken at 20 m inDecember 1992 on firm substrates and in March1993 on sandy bottom (Hohenegger, 1994) showthe same bimodal distributions as the 20 m sampletaken in June 1996 characterized by a higher pro-portion of the smaller-sized subgroup. Because thesubgroups do not shift in parameter position dur-ing seasons, interpretation as different cohorts seemsinappropriate. Designation of generations are alsodifficult, since proportions remain more or less con-stant from 10 to 40 m. Specimens from 40 m thathave be studied for reproduction (Dettmering, 1997)belong to the second subgroup according to their testsize. They all produced gametes, and are thereforecertainly gamonts. Members of the group with testsizes >2.5 mm reproduced asexually and were inter-preted as agamonts even though proloculus size wasnot measured (Dettmering, 1997). The remaininggroup with small test sizes which is separated fromthe ‘gamonts’ by a clear discontinuity in frequencydistribution is interpreted as schizonts, and their pro-portion remains more or less constant down to 40 m.Both samples from 50 m (transects and Nakanosereef) clearly have more small-sized specimens. Onlyone sample (May 1993, 70 m; Hohenegger, 1994)had a higher proportions of ‘gamonts’ (65%) versus‘schizonts’ (35%). This may indicate that the propor-tion of ‘schizonts’ also decrease with depth, althoughthis is not evident in the investigated area due to thebroad depth range of this species.

Neorotalia calcar is abundant in very shallowwaters with high irradiance, protecting against UV-radiation by hiding between algal thalli, where itlives strongly fixed by pseudopods extruding fromthe spines. Fewer smaller macroalgae in the south-ern transect, combined with a lower food availabil-ity, may be responsible for the low settlement inthis area, which is typical for all members of Cal-carinidae.

Calcarina gaudichaudii is the dominant ‘starsand’ foraminifer inhabiting shallow regions of thefrontal reef crest, especially in the northern Ryukyus.Here, it densely settles in pools, clinging to thalli ofsmall macroalgae with its spines. Thick tests and


the shadow of algae may help to prevent geneticdamage by UV-radiation. The small number of C.gaudichaudii living on the crest and reef edge in thesouthern transect can be explained by the few crestpools here and the low density of smaller macroalgaethat are necessary for attachment. Unstructured coralrocks and components in the uppermost reef slopealso hinder the strong fixation to the substrate thatis necessary to resist major hydrodynamic forces.Additionally, the greater amount of nutrients in thenorthern transect enable uptake by the foraminifer,similar to corals (Patterson et al., 1991), despitelacking apertures for feeding (Rottger and Kruger,1990).

Interpretation of subpopulations is difficult on thebasis of test sizes. While Rottger et al. (1990b) sug-gest a trimorphism (not yet verified for calcarinids),an explanation as cohorts of gamonts or schizontsis also possible, as proposed by Sakai and Nishi-hira (1981) for the related species Baculogypsinasphaerulata, which has similar ecological niches.Detailed investigation of reproduction and popula-tion dynamics are necessary to solve this problem.

Calcarina defrancii avoids highest energy envi-ronments, where the small tests with fragile spineswould be crushed. Fixation to the substrate is not asstrong as in C. gaudichaudii, and this species thusneeds well-structured surfaces to resist water turbu-lence. This explains the depth distribution, whichstarts and peaks at 10 m on well-structured firm sub-strates in the northern transect, while the maximumis reached at 20 m on less structured larger compo-nents in the southern part. Again, different nutrientlevels could be responsible for much higher abun-dance in the upper slope of the northern transect.

No agamonts with typical bifurcating spines werefound in the samples probably due to the low num-bers found. Interpretation of the remaining homo-geneous population as gamonts or schizonts requirefurther studies on reproduction and population dy-namics.

High frequencies of the defrancii morphotype ofCalcarina hispida in the northern transect may beexplained by higher nutrient levels and greater avail-ability of firm substrates in deeper parts here versusthe predominance of sands in the southern areas.

Large-sized individuals interpreted as agamontsdiffer from all investigated individuals by larger test

size, spine number and form. They are not repre-sented in the samples despite the large number ofinvestigated specimens. Differentiation of the mainpopulation into two subgroups may be interpreted asgenerations, as indicated by constancy in distribu-tion parameters and the proportion shift: a distinctdesignation as schizonts or gamonts needs further in-vestigation on reproduction processes and populationdynamics.

Uppermost slope parts except the reef crest areinhabited by the spinosa morphotype of Calcarinahispida in higher numbers; this supports the des-ignation of both forms as different ecophenotypes.The latter morphotype replaces the defrancii typeon firm and well-structured substrates in the shal-lower slope of the northern transect and dominatesthe foraminiferal fauna at 10 and 20 m. Althoughhigh abundance in the shallower parts characterizesits depth distribution, the spinosa morphotype avoidsthe extreme water turbulence of the reef crest re-gion. Less numerous larger components and theirmore unstructured surfaces in the southern transectmay be responsible for the extremely few individualsinhabiting this region.

Despite the high number of investigated speci-mens, no agamonts characterized by multiple spinescould be found. Differentiation into two subgroups ismuch clearer than in the defrancii morphotype, butidentification of generations needs further research.

Baculogypsinoides spinosus is the only calcarinidthat prefers calm water and low light intensities. Itsettles on firm substrates fixed to the substrate byprotoplasm extruding from the strong spines. Sandybottoms were less frequently inhabited, especiallyin the deepest parts of the distribution range distin-guished by low proportions of larger components.

A few agamonts characterized by much largertests and a higher number of thick spines were foundin deeper parts of the slope. The second subgroup’sincrease in proportion with depth supports the inter-pretation as ‘gamonts’. This confirms the assump-tion that asexual reproduction leading to small-sized‘schizonts’ is the main form of reproduction in thehigh energetic regions of the species’ distributionrange. This is illustrated by B. spinosus, in whichonly small-sized individuals predominate at 20 m.

The habitat of Baculogypsina sphaerulata is sim-ilar to that of C. gaudichaudii, differing only in the


strong restriction to the reef crest and avoidanceof the uppermost slope. Both species are the mainrepresentatives of ‘star sand’ foraminifers inhabitingreefs in the tropical and subtropical Northwest Pa-cific, where they reach extremely high abundances.While the proportion of C. gaudichaudii is higher in‘star sands’ of the northern Ryukyus, B. sphaerulatabecomes the main component of ‘living sand’ in thesouthern islands of the archipelago.

According to the interpretation by Sakai andNishihira (1981), subpopulations of different testsizes can be interpreted as cohorts of asexually re-producing schizonts, with more younger individualsthan ‘adults’. Also, test size of the ‘adults’ coincidewith the data given in Sakai and Nishihira (1981).This does not rule out interpretation as differentgenerations, since the smaller-sized group, mostlyregarded as ‘schizonts’, is more abundant than thelarger ‘gamonts’; this is typical for extreme hy-drodynamic conditions, where sexual reproductionbecomes difficult. Further investigation on repro-duction and population dynamics may solve thisproblem.

The semi-involute nummulitid Operculina am-monoides prefers lower energy environments withmedium light intensities. Settlement in shallowerwaters is restricted to firm substrates with well-structured surfaces, where resistance against hydro-dynamic forces is possible by hiding within smallgrooves and holes. Abundance is higher on sandybottoms than on hard substrates in both transects.This may reflect better nutrients availability in softsediments (Pecheux, 1995). Replacement of O. am-monoides by the evolute and larger sister species O.complanata on sand below 50 m is reflected in clearbimodal test size distributions in both investigatedtransects and in samples taken in 1993 (Hohenegger,1994, 1995).

The clear differentiation into two subgroups ac-cording to test size and the few extremely largeindividuals hint at generation differences. All spec-imens larger than 4 mm may be regarded as aga-monts. Interpretation of both subgroups with smallertests is difficult. Individuals with larger tests belong-ing to the second subgroup may represent gamonts.This conclusion is confirmed through the releaseof gametes by an O. complanata individual from70 m that falls into the second subgroup of O. am-

monoides according to test size (Rottger et al., 1998).Interpretation of the smaller-sized specimens in thefirst subgroup is problematic, since both readings asschizonts or a cohort of gamonts is possible. Onlyinvestigation on reproduction can relieve this prob-lem, since all measurements on test size, proloculussize or test growth did not provide clear determina-tion (Fermont, 1977; Pecheux, 1995). Differences intest sizes between the two 50 m samples (transectsand Nakanose) may be explained by the shalloweronset of the larger O. complanata in the Nakanosearea; this opinion requires confirmation by X-rayinvestigation.

Nummulites venosus weakly attaches to the sub-strate and its thick lenticular test cannot resist strongwater movement on hard bottom. Sands in high en-ergy regions of the uppermost slope are also avoidedby N. venosus because sediment motion may crushthe tests especially in agamonts. Settlement is there-fore restricted to the sandy deeper slope. Decreasingwater energy with depth correlates to the increasein frequencies of large individuals, which are inter-preted as agamonts, attaining the highest proportion(70–80%) of all larger foraminifers in the deepestparts of their distribution range.

Interpretation of test size differences within pop-ulations of N. venosus is as difficult as for O. am-monoides. Large-sized individuals (>4 mm) withflattening chambers at the test periphery can easilybe recognized as agamonts; they reproduce asexuallyunder laboratory conditions (Kruger, 1994). Culturedbrood of this generation released gametes at a meansize of 3 mm (Rottger et al., 1998). This correspondsexactly to sizes of the second subgroup, support-ing the interpretation as gamonts. The remainingsubgroup with smallest tests may be identified asschizonts, but an interpretation as a cohort of grow-ing gamonts is also plausible based on the generationlongevity of 1.5 years (Rottger et al., 1998) in com-bination with an annual breeding season.

Heterostegina depressa shows the widest depthrange of all larger foraminifers and keeps its testsizes relatively constant. Its depth distribution startsin pools on the outer reef crest and goes down to80 m. The transition to the reef crest is remarkable,especially in the southern transect, where this speciesis abundant in crest pools because competitive cal-carinids are rare. Well-structured surfaces on hard


bottoms of the shallow slope are favored settlementsites in high energy environments, but sands are alsoinhabited, especially in the deeper parts below 50 m.The high number of H. depressa living on sand inthe southern transect may be explained on the onehand by erosion from smooth hard bottoms throughhydrodynamics, on the other by the lower proportionof components, which effects higher settlement onsands. The latter substrate does not represent as greata barrier for H. depressa as for other species such ascalcarinids.

Interpretation of test size differences is supportedby the large number of studies on reproduction (e.g.,Rottger, 1972; Rottger et al., 1986, 1990a; Kruger,1994) making H. depressa the best investigated fo-raminifer in this respect. Gamonts reproduce in thelaboratory at mean test sizes of 4 mm; the third sub-group of the investigated samples demonstrating thesame parameter values must therefore be interpretedas gamonts. Outliers exceeding 5.5 mm may repre-sent agamonts that can be found in small numbers atdepths below 40 m. Both subgroups with smaller testsizes coincide with schizonts of laboratory culturesin distribution parameters. Differentiation into twosubgroups is not significant for the shallow samplesfrom the reef edge down to 20 m, but becomes sig-nificant for deeper parts. This differentiation can beinterpreted as cohorts, since longevity in schizontsis shorter (3 to 6 months) than in gamonts (5 to 8months; Kruger, 1994).

Acknowledgements

This work was supported by the Austrian Sci-ence Foundation FWF Project P10946-GEO “Re-lations between biocoenoclines and taphocoeno-clines”. Thanks are due to the whole staff of theTropical Biosphere Research Center, Sesoko Station,University of the Ryukyus, especially Kiyoshi Ya-mazato and Kazunori Takano, who made field workduring the 4-months stay as an invited researcherfor the senior author possible. Shigeo Nakamura washelpful in sampling. The main part of this paper waswritten during a 7-month stay of the senior authoras a visiting professor at the Kagoshima UniversityResearch Center for the South Pacific, Japan, whileworking on the geographical distribution of larger

foraminifera in the Northwest Pacific. Problems offoraminiferal biology, distribution, and sedimentol-ogy were discussed with Kimihiko Oki, Akio Hatta(Kagoshima University), and Rudolf Rottger, Uni-versitat Kiel, Germany. Michael Stachowitsch (Uni-versitat Wien) corrected the English text.

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Habitats of larger foraminifera on the upper reef slope of Sesoko Island, Okinawa, Japan

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