Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190www.elsevier.nl/locate/palaeo

A comparison of living and dead molluscs on coral reefassociated hard substrata in the northern Red Sea —

implications for the fossil record

Martin Zuschin a,*, Johann Hohenegger a, Fritz F. Steininger ba Institut fur Palaontologie, Universitat Wien, Althanstraße 14, A-1090 Vienna, Austria

b Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany

Received 4 May 1999; received in revised form 7 December 1999; accepted for publication 22 December 1999

Abstract

Fidelity of death assemblages to live shelly faunas is one of the major palaeontological questions, but quantitativedata are scarce and most case studies on this topic have been performed in non-reef sediments. Therefore we studieddifferent types of subtidal reef-associated hard substrata (reef flats, reef slopes, coral carpets, coral patches, rockgrounds), each with different coral associations, in order to determine the agreement of assemblages of living anddead shell-bearing molluscs. A total area of 340.5 m2 was investigated and 2846 individuals were counted at 68 samplelocalities ranging from shallow subtidal to 40 m water depth. Most taxa found dead in the study area were also foundlive and vice versa; differences in this respect can be related to quantitatively unimportant taxa. However, strongdifferences exist in the proportion of living and dead fauna, dominant taxa, and molluscan distribution patterns. Theratio of live to dead molluscs is high. Living molluscs are strongly dominated by taxa with distinct relations to corals,mainly Pedum, Coralliophila and Tridacna, and the encrusting gastropod Dendropoma. Five distinct groups of livingmolluscs can be differentiated and related to specific hard substrata, which are characterized by distinct molluscanlife habits. In contrast, the death assemblages are always strongly dominated by encrusting bivalves, mainly Chamoideaand Spondylidae, and cerithiid gastropods in varying dominances. Correspondingly there is no significant correlationof the total abundance of living and dead molluscs and their overall similarity is only 6%. Similarity between livingand dead faunas is above 50% at only 12 of the 68 sample locations, and at 17 sample locations significant correlationsof living and dead molluscs were recognized. These correlations are mainly based on Chamoidea, which dominateboth the living and dead fauna, on rock grounds. Therefore rock grounds are the only bottom type with consistentcorrelations and similarities of living and dead molluscs. The observed bias is due to the close relationship ofmolluscan life habits and post-mortem history of shells. Molluscs that live permanently attached to or within livingcorals (mostly bivalves and encrusting Dendropoma) can easily be overgrown after death by the large amounts ofliving substrata available. Rapid transport of dead shells into surrounding sediments or into crevices within corals istypical of gastropods that feed on corals. Molluscs that colonize dead surfaces preferentially accumulate on rockgrounds. The ecologic information that can be derived from the shells depends on the different post-mortem historiesof the faunas. © 2000 Elsevier Science B.V. All rights reserved.

Keywords: mollusca; taphonomy; palaeoecology; coral reef; recent; Red Sea

* Corresponding author. Fax: +43-1-31336-784.E-mail address: martin.zuschin@univie.ac.at (M. Zuschin)

0031-0182/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0031-0182 ( 00 ) 00045-6

168 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

1. Introduction (sensu Bromley, 1975), rock grounds (sensuGoldring, 1995), cobbles (e.g. Surlyk andChristensen, 1974; Wilson, 1987) and a wide rangeOne of the major questions in considering the

quality of the fossil record is how accurately shelly of skeletons (e.g. Nebelsick et al., 1997; Zuschinand Piller, 1997a), most of which might be referreddeath assemblages preserve the composition and

structure of the shelled portion of the original to as shell grounds (after Dodd and Stanton,1990). Coral colonies, in contrast, are not only thecommunity (see review by Kidwell and Bosence,

1991). In spite of its importance, only few tapho- primary frame builders of coral reefs (for a reviewsee Scoffin, 1992), but are also the major type ofnomic investigations in modern environments have

provided data to answer this question, and com- hard substrata characterized by a living surface.Large parts of coral reefs provide such a livingparisons between living and dead faunas in marine

environments are mainly restricted to molluscan surface (e.g. Liddell and Ohlhorst, 1988) and,especially among molluscs, a wide range of taxaassemblages in soft sediments (e.g. Cadee, 1968;

Warme, 1969, 1971; Staff et al., 1986; Carthew and and different life habits are closely linked to suchsubstrata (e.g. Hadfield, 1976; Morton, 1983a;Bosence, 1986; Fursich and Flessa, 1987; Flessa

and Fursich, 1991). However, after removing sam- Kleemann, 1990, 1992; Schuhmacher, 1993).The coral-dominated shallow marine sub-pling artifacts, the agreement between live:dead

assemblages in these studies is generally considered tropical Northern Bay of Safaga (Fig. 1) is com-posed of various sedimentary facies that are closelyto be high (for reviews see Kidwell and Flessa,

1995; Kidwell, in press). Only a few studies com- associated with different types of hard substrata,including reef flats, reef slopes, coral carpets, coralpare the living and dead faunas of hard substrata

(e.g. Pandolfi and Minchin, 1995; Pandolfi and patches and rock bottoms (Piller and Pervesler,1989). These types of hard substrata are charac-Greenstein, 1997a; Greenstein and Pandolfi, 1997),

and to our knowledge there is no study dealing terized by different coral associations and bydifferent degrees of surface coverage (Riegl andquantitatively with the distribution of living and

dead molluscs in coral reef environments, which Velimirov, 1994; Riegl and Piller, 1997). The distri-butions of living bivalves are correlated withusually provide a close interfingering of living and

dead hard substrata. environmental gradients and the molluscan assem-blages characteristic of the different facies haveThe relation between live and dead assemblages

of hard and soft substrata probably differs signifi- different life/death ratios (Zuschin and Piller,1997b,c).cantly, because of some important differences

regarding composition of living communities and The objectives of the present study are to: (1)evaluate the degree of coincidence between livingaccumulation of their hard parts. Soft sediments

are mainly colonized by sessile or vagile infauna and dead molluscan faunas in a setting of mixedliving and dead hard substrata, and (2) determineand epifauna, and their shelly death assemblages

often map communities better than any single the influence of substratum type and molluscanlife habits on live:dead agreement.census of the living shelled community (e.g.

Carthew and Bosence, 1986). This is due to timeaveraging and low aggradation rates in mostmarine sediments, which smooth out the patchy 2. Materials and methodsdistribution of most communities (for a review seeKidwell and Bosence, 1991). In contrast, most Different subtidal hard substrata were sampled

for shelled molluscs at 68 localities (Fig. 2, Table 1)types of hard substrata provide a dead surfacethat is mainly populated by encrusting and endo- with a 0.25 m2 aluminium square frame. At each

locality the location of the first frame was selectedlithic colonizers. These usually become entombedin their life sites and thus allow the detailed study randomly, the following frames were positioned

along a line extending from the point. In mixedof faunal succession (Brett, 1988). Among suchhard substrata are, for example, hard grounds hard substrata/loose ground and/or soft-bottom

169M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Fig. 1. Location map and general bathymetry of the study area (after Piller and Pervesler, 1989). Dense stippled fields in the rightmap are intertidal areas. AM=aerial mast, H=‘Safaga Hotel’.

habitats, frames were only placed on hard substra- (Table 2). The present study is based on quantita-tive samples from the seafloor and from easilytum. A mean of 5.0 m2 (±1.7) of seafloor was

investigated per locality, with a range from 3 to accessible cavities. Due to methodological limita-tions, deeper cavities within coral reefs have not11 m2 (Table 2). The number of investigated

frames depended on mollusc density ( low density been considered (e.g. fig. 6 in Scoffin, 1992).Samples were taken during daylight (usuallyrequired a higher number of frames and vice versa)

and on water depth (greater water depths required between 10 am and 5 pm). The molluscs wereidentified either immediately in their environmentshorter dive times). The mean water depth was

14.3 m (±9.9) with a range from 1 to 40 m (most bivalves and sessile gastropods) or were

170 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

collected (many vagile gastropods) for moredetailed investigation. The fauna was separatedinto live and dead individuals and hermit crab-occupied shells. The information on live and deadindividuals was used for the statistical analysis;shells occupied by hermit crabs were treated as animportant descriptive feature affecting the distribu-tion of dead gastropod shells.

Due to a highly questionable taxonomy,Chamoidea, Spondylidae and Ostreoidea, exceptfor Lopha cristagalli, were not differentiated tospecies level; most of the taxonomic studies in factmainly describe ecophenotypes (Oliver, 1992,1995). Some other taxa were identified only abovethe species level due to problems with identificationin the field or poor preservation (e.g. Conus spp.).

It is difficult to recognize smaller molluscs bySCUBA diving. Therefore, to provide a consistentdatabase, molluscs<2 cm were excluded from thequantitative treatment. Most boring bivalves (e.g.gastrochaenids, lithophagins) have been excludedfrom the quantitative collection because they aredifficult to identify from the surficial appearanceof their small bore holes. A qualitative study ofboring bivalves has been presented by Kleemann(1992).

The complete database contains 54 taxa, butstatistical analysis was confined to the 18 taxa thateach contribute more than 1% to either the live orFig. 2. Sample locations. AM=aerial mast, H=‘Safaga Hotel’.dead mollusc content of all samples (Fig. 3,

Table 1Classification of the investigated hard substrata and corresponding assignment of sample sites. Classification of hard substratamodified after data provided in Piller and Pervesler (1989), Riegl and Velimirov (1994) and Riegl and Piller (1997, 1999)

Hard substrata Coral associations Living coral coverage (%) Sample locations

Reef flats Stylophora association 30 1, 2, 3Reef slopes Acropora association 40–80 15, 16, 17

Porites association 50–100 18, 19, 20Acropora–Millepora association 50 25, 26, 27, 38Porites–Millepora association 80–100 14Stylophora association <20 64

Coral carpets Porites association 60–90 4, 21, 59, 62, 63, 66, 67, 68faviid association 20–30 5, 7, 9, 11, 12, 13, 29, 30, 32, 33, 34,

35, 41, 43, 44, 47, 48, 51, 53, 58, 60, 61depauperate faviid association <20 6, 36, 37, 50

Rock grounds Sarcophyton association 10–20 10, 22, 31, 46, 55, 56, 57platy scleractinian association 30–50 8, 23, 42, 45, 49, 52, 54, 65

Coral patches Acropora patch association 60–80 24, 28, 40Stylophora–Acropora patch association 60–80 39

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Fig. 3. Plots of cumulative molluscan diversity versus numbers of sampling sites. (A) Life assemblages combining all sample locations.(B) Death assemblages combining all sample locations. (C) Life assemblages (reduced data set) of major hard substrata types. (D)Death assemblages (reduced data set) of major hard substrata types.

Table 3). These comprise more than 97% of live Using the origin (frequency=0) as the naturalangle vertex, this coefficient also avoids negativeindividuals and more than 94% of dead individuals

of the original, complete data set. The 1% limit values found in product moment correlationcoefficients. The latter are caused by the positionwas chosen due to the properties of proportion

statistics, where the influence of smallest propor- of the angle vertex in the gravity centre of themultidimensional distributions, which stronglytions could bias statistical treatment (Fleiss, 1973;

Linder and Berchtold, 1976). depends on the distribution of variables (e.g.Hohenegger, 1974, 1982).The congruence of live and dead assemblages

(fidelity) was measured in several ways. Indices As the squared cosine coefficient cannot betested for significance, congruence of live and deadprovided in Kidwell and Bosence (1991) were used

to calculate the percentage of (1) taxa found live assemblages was also measured on the basis of thesignificance level of Spearman’s rank correlationthat are also found dead, (2) taxa found dead that

are also found live, and (3) dead individuals of coefficient, because Kolmogorov–Smirnov andShapiro–Wilk tests strongly rejected the hypothesistaxa found alive, from both the original and the

reduced data set. of normally distributed data.As most taxa within any one association areThe proportions of living and dead molluscs

were compared using two methods. Congruence in present in other associations as well, ordinationmethods were used to clarify the distributionpercentages was measured using the squared cosine

coefficient on absolute frequencies (e.g. Orloci, pattern of molluscs and the relations between taxaand sites. Because frequency data are represented1966). This coefficient is similar to the product

moment correlation coefficient in measuring angles in a contingency table, correspondence analysis asan ordination method was used for data reductionbetween samples, but has the important advantage

of being independent from distribution form. (Benzecri, 1992; Hill, 1973). The advantage of this

172 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Table 2Basic data on sample locations (water depth, investigated area, molluscan density) and results of correlation and similarity analysison living and dead molluscs. Bold type=1% significance level, underlined type=5% significance level

Site Water Investigated Mollusc density (per 0.25 m2) % Similarity Significancedepth (m) area (m2) level

Living fauna Dead fauna

Mean St. dev. Min. Max. Mean St. dev. Min. Max.

1 1 4.5 11.8 8.2 0 30 0.2 0.5 0 2 0.0 0.7932 1 8 2.3 3.0 0 13 0.2 0.4 0 1 22.7 0.1053 1 5.75 5.0 6.7 0 25 0.1 0.5 0 2 0.0 0.7764 6 3 9.3 6.1 2 21 0.1 0.3 0 1 32.0 0.0245 10 3 2.8 2.6 0 10 1.3 1.1 0 3 67.6 0.0006 6 4 1.8 1.4 0 5 1.0 0.7 0 2 61.8 0.0007 15 4 0.8 1.2 0 4 0.6 0.7 0 2 63.9 0.0008 23 3 1.1 1.2 0 4 1.7 1.6 0 5 98.7 0.0009 18 3 1.8 3.1 0 11 0.4 0.7 0 2 26.3 0.08610 24 3 0.4 0.8 0 2 1.5 1.2 0 4 49.8 0.00211 17 4 1.6 3.8 0 13 0.3 0.6 0 2 0.0 0.74712 17 4 0.9 1.5 0 5 0.6 0.6 0 2 29.0 0.10313 12 4 2.6 3.4 0 13 1.0 1.3 0 4 12.6 0.51214 1 6 1.3 1.8 0 6 0.0 0.0 0 0 0.0 –15 13 6 0.6 1.1 0 4 0.1 0.3 0 1 0.6 0.95416 8 6 0.1 0.3 0 1 0.3 0.9 0 4 16.7 0.26517 5 6 0.7 0.9 0 2 0.1 0.4 0 2 4.0 0.91318 6 3 9.5 5.9 1 20 0.3 0.7 0 2 24.8 0.08019 4 3 3.5 2.8 0 8 0.0 0.0 0 0 0.0 –20 2 3 6.4 2.5 4 13 0.0 0.0 0 0 0.0 –21 10 6 2.3 1.5 0 5 0.2 0.4 0 1 69.9 0.00022 28 3 0.3 0.5 0 1 0.8 1.1 0 4 78.8 0.00023 30 6 0.0 0.0 0 0 0.0 0.2 0 1 0.0 –24 4 3 1.5 1.8 0 6 0.6 0.7 0 2 11.0 0.41425 9 6 0.7 1.1 0 3 0.3 0.6 0 2 0.0 0.53126 5 6 1.1 2.0 0 9 0.0 0.2 0 1 0.0 0.55327 5 8 1.4 2.4 0 12 0.4 0.9 0 3 6.2 0.64628 11 6 1.6 3.1 0 14 0.4 0.5 0 1 0.9 0.98129 12 6 0.9 1.3 0 4 0.3 0.6 0 2 1.7 0.79630 18 11 0.6 0.8 0 3 0.1 0.3 0 1 21.0 0.13631 6 5.25 0.9 1.0 0 3 1.1 1.5 0 7 78.6 0.00032 11 8 2.5 3.0 0 15 0.1 0.4 0 2 7.5 0.57733 20 6 1.0 1.1 0 4 0.1 0.3 0 1 0.1 0.61234 9 6 2.4 2.0 0 10 0.4 1.0 0 4 8.1 0.56335 15 4 1.9 1.9 0 6 0.4 0.6 0 2 5.0 0.61736 6 6 1.6 1.8 0 6 0.4 1.0 0 4 19.2 0.19837 10 6 1.1 1.3 0 4 0.3 0.6 0 2 22.4 0.22238 16 6 0.8 1.6 0 7 0.1 0.3 0 1 1.9 0.97139 7 7 1.3 1.5 0 6 0.1 0.4 0 1 2.9 0.77240 4 6 0.4 0.8 0 3 0.6 0.8 0 3 35.9 0.01941 15 8 0.5 0.9 0 4 0.4 0.7 0 3 4.8 0.67342 33 7 0.1 0.4 0 2 0.4 0.5 0 1 97.0 0.00043 22 7 0.6 0.8 0 3 0.3 0.5 0 2 1.5 0.74244 19 8 0.7 1.4 0 7 0.2 0.5 0 2 0.1 0.61045 30 4 0.2 0.4 0 1 0.3 0.4 0 1 8.3 0.63746 17 3.5 0.9 0.9 0 3 2.0 1.7 0 5 95.1 0.00047 25 7 0.7 1.1 0 4 0.3 0.5 0 2 1.5 0.91548 34 5 0.4 0.9 0 3 0.4 0.7 0 3 1.0 0.790

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Table 2 (continued )

Site Water Investigated Mollusc density (per 0.25 m2) % Similarity Significancedepth (m) area (m2) level

Living fauna Dead fauna

Mean St. dev. Min. Max. Mean St. dev. Min. Max.

49 40 5 0.0 0.0 0 0 0.2 0.4 0 1 0.0 –50 6 5.5 1.4 1.7 0 6 1.5 2.2 0 10 33.9 0.04851 26 3 0.8 1.3 0 4 1.2 1.7 0 5 75.5 0.00052 30 4 0.1 0.3 0 1 0.5 0.7 0 2 13.3 0.20953 14 5 2.7 3.9 0 15 0.5 1.1 0 5 5.9 0.62254 38 6 0.2 0.7 0 3 0.1 0.3 0 1 4.5 0.67155 11 3 2.3 2.2 0 8 2.5 1.8 0 5 95.1 0.00056 6 3 1.4 1.4 0 5 1.0 1.0 0 3 18.3 0.15457 30 3 1.5 1.2 0 4 4.8 3.2 0 10 97.8 0.00058 18 6 0.3 0.5 0 1 0.2 0.4 0 1 43.3 0.00659 6 4 8.9 7.0 2 28 0.0 0.0 0 0 0.0 –60 17 4 1.9 2.1 0 8 0.7 1.5 0 6 10.3 0.62861 10 4 2.0 1.9 0 7 0.9 1.6 0 4 18.1 0.31462 20 4 0.8 2.2 0 9 0.1 0.3 0 1 0.0 0.74263 10 4 1.6 4.2 0 16 0.3 0.7 0 2 0.0 0.66864 5 4 0.1 0.3 0 1 0.1 0.3 0 1 0.0 0.81765 30 4 0.0 0.0 0 0 0.1 0.3 0 1 0.0 –66 20 4 0.7 0.9 0 2 0.3 0.4 0 1 0.0 0.47667 10 4 1.4 2.4 0 9 0.3 0.6 0 2 9.7 0.33068 5 4 1.4 2.2 0 8 0.2 0.8 0 3 0.0 0.695

Total area 1.62 3.14 0 30 0.47 1.03 0 10 6.0 0.939

method is the direct derivation of frequencies observations and modified for the present mollus-can study.without transformations and the simultaneous rep-

resentation of sites and taxa within the same Reef flats are rock bottoms colonized by a coralassemblage that is depauperate due to regularsystem of axes in the form of biplots (Gabriel,

1971). The first three dimensions of the correspon- exposure during low tides. Thick extensive crustsof coralline red algae are a typical feature of thisdence analysis (e.g. Gauch, 1982) were used for

the interpretation of data. Sample groups estab- bottom type.Reef slopes border the fringing reefs and patchlished by this analysis were described with respect

to the dominant and characteristic molluscan reefs of the Northern Bay of Safaga. They areassociated with strong energy gradients and/orfauna. All the statistical analyses were performed

using the software package SPSS 8.0. steep relief and can be differentiated intoAcropora–, Porites–, and Acropora–Millepora reefslopes on the basis of their typical coral assem-blages. A few of the studied sites are characterized3. Hard substrata typesby coral associations different from the commonones and by different environmental conditionsThe hard substrata studied are distinguished by

coral associations and coverage of living surface (Table 1). Two sites are located in very shallowsettings: at sample location 14, Millepora dicho-(Table 1). In general, the classification of hard

substrata utilized here follows the terminologies toma is superimposed on a base consisting ofPorites. At sample location 64, the scleractiniansand descriptions of Piller and Pervesler (1989),

Riegl and Velimirov (1994) and Riegl and Piller Stylophora and Pocillopora are scattered on a rockground. Sample locations 52 and 65 are deeper(1997, 1999); these are augmented by our own

174 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Table 3Ecological properties of the 18 most abundant taxa and their corresponding classification into six life habit groups using integratedtaxonomic and life habit information. Group 1: bivalves associated with living corals. Group 2: bivalves encrusting dead hardsubstrata. Group 3: bivalve crevice dwellers in dead hard substrata. Group 4: encrusting gastropods. Group 5: gastropods feedingon living corals. Group 6: gastropods that avoid living corals

Taxon Substrate relations Feeding strategy Classification

Barbatia foliata (Forsskal, 1775) byssally attached in crevices of living Porites spp. suspension feeder 1Barbatia setigera (Reeve, 1844) byssally attached in crevices of dead hard substrate suspension feeder 3Chamoidea encrusted to dead hard substrates suspension feeder 2Ctenoides annulata (Lamarck, 1819) byssally attached in crevices of dead hard substrate suspension feeder 3Isognomon legumen (Gmelin, 1791) byssally attached in crevices of dead hard substrate suspension feeder 3Lima lima (Linnaeus, 1758) byssally attached in crevices of dead hard substrate suspension feeder 3Lopha cristagalli (Linnaeus, 1758) encrusted to dead hard substrates suspension feeder 2Ostreoidea encrusted to dead hard substrates suspension feeder 2Pedum spondyloideum (Gmelin, 1791) boring and byssally attached in living coral suspension feeder 1Pteriidae byssally attached to living corals suspension feeder 1Spondylidae encrusted to dead hard substrates suspension feeder 2Streptopinna saccata (Linnaeus, 1758) byssally attached in crevices of living and dead suspension feeder 1

hard substrateTridacna maxima (Roding, 1798) byssally attached among corals or within corals various food sources 1Cerithium spp. vagile on hard substrates algal detritus feeder 6Conus spp. vagile on hard substrates predator 6Coralliophila neritoidea (Lamarck, 1816) vagile on living Porites spp. parasitic 5Dendropoma maxima (Sowerby, 1825) encrusted to living corals/dead hard substrates suspension feeder 4Drupella cornus (Roding, 1798) vagile on living corals (acroporans) predator 5

reef slope settings and consist of rock grounds Coral patches (sensu Piller and Pervesler, 1989)are a special reef type, which is widespread in thewith a patchy platy scleractinian cover.

Coral carpets (sensu Reiss and Hottinger, 1984) Northern Bay of Safaga, commonly occurring inshallow water on sandy substrata. Coral patchesoccur over wide areas of the Northern Bay of

Safaga, to a depth of 40 m; they are up to 3 m are only a few metres in diameter and do not showa clear ecological zonation (Riegl and Piller, 1999).thick in shallow settings. Coral carpets build a

framework, but lack a distinct zonation since they They can be differentiated into two major groupsbased on their coral composition: Acropora– andonly grow in areas without distinct gradients (Riegl

and Piller, 1999). On the basis of coral assemblages Stylophora–Acropora coral patches; typically coralpatches grade into faviid carpets.they can be differentiated into Porites and

faviid carpets, which grade into one another.Depauperate faviid carpets are characterized byless than 20% of living coral coverage (Table 1). 4. Life habits of molluscsOn coral carpets, the highly variable heights ofindividual coral colonies create diverse molluscan The 18 taxa considered in the statistical analysis

consist of 13 bivalves and five gastropods, whichhabitats.Rock grounds (sensu Goldring, 1995) consist of are classified using integrated taxonomic and life

habit information provided in Fankboner and Reidnon-framework building Sarcophyton carpets(Riegl and Piller, 1999) on bare rocky surfaces (1990), Goreau et al. (1973), Hadfield (1976),

Hughes and Lewis (1974), Kleemann (1992),and platy scleractinian carpets, where distinct mol-luscan habitats are lacking except for the high Kohn (1983), Kohn and Leviten (1976), Leviten

and Kohn (1980), Morton (1983a,b), Reicheltamount of exposed coral limestone between thefaviid corals with platy growth forms (Table 1). (1982), Robertson (1970), Taylor (1971), Taylor

175M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

and Reid (1984), Schuhmacher (1993), Zuschin assemblage. The percentage of dead individualsthat are from taxa found alive is greater than 96%and Piller (1997b,c) and from our own field obser-

vations (Table 3). for the complete data set and is 100% for thereduced data set (Table 5).Group 1 consists of bivalves that have a close

substrate relation to living corals: these taxa bore The dominant taxa in the live and dead assem-blages are strikingly different, however. Livingin living corals (Pedum), settle in crevices of living

corals (B. foliata and Streptopinna), are epizoic on molluscs are strongly dominated by bivalves asso-ciated with living corals, especially Pedum andliving corals and the hydrozoan Millepora

(Pteriidae), or live in close association with living Tridacna, the encrusting gastropod Dendropoma,and gastropods feeding on corals, mainly repre-corals (Tridacna). Group 2 consists of bivalves that

are encrusters on dead hard substrata (Chamoidea, sented by the parasitic Coralliophila. Dead mol-luscs, in contrast, are strongly dominated byOstreoidea and Spondylidae). Group 3 consists of

bivalves that are crevice dwellers of dead hard encrusting bivalves, especially Chamoidea andSpondylidae. Overall, in the reduced data set gas-substrata (Barbatia setigera, Ctenoides annulata,

Isognomon legumen, Lima lima). Group 4 consists tropods make up 36% of the living molluscs butonly 8% of dead molluscs; more than 73% of theof the encrusting gastropod Dendropoma, which

shows a rather indifferent relation to living or dead shells of dead gastropods were inhabited by hermitcrabs (Table 4) (the corresponding values for thehard substrata because it occurs on both types.

Group 5 consists of vagile gastropods that have a complete data set are 37%, 11% and 66%).In accordance with the strong differencesclose feeding relation to living corals (Coralliophila

and Drupella). Group 6 consists of vagile gastro- regarding the dominating taxa, no statisticallysignificant correlation between the total abundancepods that try to avoid living corals (Conus spp.

and Cerithium spp). of living and dead molluscs exists, the overallsimilarity being only 6% (Table 2). 17 samplelocations display a significant or highly significantcorrelation of live and dead assemblages. They5. Comparison of live and dead molluscsbelong to rock grounds (8, 10, 22, 31, 42, 46, 55,57), coral carpets with Porites, faviid and depau-5.1. Congruence of live and dead assemblages

(fidelity) perate faviid associations (4, 5, 6, 7, 21, 50, 51and 58) and Acropora patch associations (40).Only at 12 of these sample locations is the sim-At 68 sample locations a total area of

340.5 m2 was investigated (Fig. 2, Table 2) and ilarity between living and dead fauna above 50%(Table 2). However, at most of these sample loca-2846 individuals were counted. Most of these

individuals were alive (2211; 77.7%) and only a tions major similarities are evident between livingand dead Chamoidea. These results are supportedminor part was dead (635; 22.3%). Generally,

molluscan densities are characterized by high by a correspondence analysis, which shows strongdifferences in the composition of living and deadstandard deviations (Tables 2 and 4), indicating

uneven distribution within and between sites. molluscs at most sample locations (Fig. 4).Corresponding to the much higher number ofliving molluscs, the overall density of living mol- 5.2. Distribution patterns of living and dead

molluscsluscs (1.62 indiv./0.25 m2) is much higher than thatof the dead fauna (0.47 indiv./0.25 m2).

The percentages of live taxa found dead and of According to the results of a correspondenceanalysis, the distribution pattern of living molluscsdead taxa found live on hard substrata in the

study area are above 60% for the complete data shows five distinct groups (Fig. 5), whereas forthe dead fauna no distinct groups can be recog-set. They are up to 100% for the reduced data set,

in which only those taxa are considered that con- nized (Fig. 6). At least four of the groups of livingmolluscs can be related to specific hard substratatribute at least 1% to either the live or dead

176 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Table 4Abundance, relative proportion and density (per 0.25 m2) of the 18 most abundant taxa. Life habit groups as in Table 3

Taxon ( life habit group) Living Dead Hermit crab inhabited

No. % Mean St. dev. No. % Mean St. dev. No. %

Pedum spondyloideum (1) 548 25.4 0.40 1.42 5 0.8 0.00 0.06 – –Dendropoma maxima (4) 387 17.9 0.28 1.99 1 0.2 0.00 0.03 – –Coralliophila neritoidea (5) 338 15.7 0.25 1.57 2 0.3 0.00 0.04 1 50.0Tridacna maxima (1) 257 11.9 0.19 0.53 33 5.5 0.02 0.15 – –Chamoidea (2) 142 6.6 0.10 0.39 318 53.2 0.23 0.79 – –Barbatia setigera (3) 87 4.0 0.06 0.33 20 3.3 0.01 0.14 – –Ctenoides annulata (3) 74 3.4 0.05 0.30 7 1.2 0.01 0.08 – –Spondylidae (2) 50 2.3 0.04 0.22 89 14.9 0.07 0.27 – –Streptopinna saccata (1) 40 1.9 0.03 0.17 1 0.2 0.00 0.03 – –Lopha cristagalli (2) 36 1.7 0.03 0.26 43 7.2 0.03 0.37 – –Barbatia foliata (1) 35 1.6 0.03 0.20 1 0.2 0.00 0.03 – –Ostreoidea (2) 34 1.6 0.02 0.20 23 3.8 0.02 0.16 – –Cerithium spp. (6) 30 1.4 0.02 0.19 30 5.0 0.02 0.17 22 73.3Pteriidae (1) 27 1.3 0.02 0.23 0 0.0 0.00 0.00 – –Isognomon legumen (3) 25 1.2 0.02 0.15 2 0.3 0.00 0.04 – –Drupella cornus (5) 20 0.9 0.01 0.31 7 1.2 0.01 0.07 6 85.7Lima lima (3) 18 0.8 0.01 0.13 7 1.2 0.01 0.07 – –Conus spp. (6) 11 0.5 0.01 0.10 9 1.5 0.01 0.08 7 77.8

Table 5Fidelity of death assemblage to living molluscs with respect to taxonomic composition after indices provided in Kidwell and Bosence(1991) and in comparison with data from soft substrata molluscs and corals. Sample groups I–V after results of correspondenceanalysis (compare Fig. 5)

% Live taxa % Dead taxa % Dead individualsfound dead found live from taxa found alive

Complete Reduced Complete Reduced Complete Reduceddata set data set data set data set data set data set

MolluscsSafaga (this study)Group I (on reef flats) 66.7 83.3 54.5 83.3 61.1 90.9Group II (on Porites associations) 50.0 60.0 60.0 75.0 45.8 50.0Group III (on rock grounds) 53.3 60.0 53.3 75.0 96.3 98.9Group IV (mainly on faviid carpets) 58.8 82.4 62.5 100.0 94.2 100.0Group V (on Acropora–Millepora reef slopes) 30.0 30.0 60.0 60.0 77.8 77.8

Study area 68.4 94.4 61.9 100.0 96.7 100.0

Non-reef mean ( Kidwell and Bosence, 1991) 87 44 83

CoralsShallow Florida Keys mean (Greenstein and Pandolfi, 1997) 67 57 69Deep Florida Keys mean (Pandolfi and Greenstein, 1997a) 77 54 56Madang Lagoon (Pandolfi and Minchin, 1995) 54 90 94

177M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Fig. 4. Ordination of samples and taxa and relationships between taxa and sites using the first two dimensions of the correspondenceanalysis on living and dead molluscs. (A) Points close to one another represent samples that are more similar in taxonomic compositionthan points farther away from one another. Note the displacement of the life assemblages from the death assemblages, suggestingdifferences in taxonomic composition between them, which can be inferred from the ordination of taxa (B). Patterns in life assemblagezonation are poorly reproduced in the death assemblages (compare also Figs. 5 and 6).

types and will be described regarding their live and within this group. Moreover, the wide dispersionof group IV samples between samples of groupsdead fauna.

The density of living molluscs is higher than II and III indicates the transitional character ofthis group (Fig. 5). Correspondingly, most of thethat of dead molluscs in four of the five differenti-

ated sample groups. Only in sample group III is recognized hard substrata are characterized by adistinct association of living molluscs. However,the dead fauna more abundant than the living

fauna (Table 6). at least two important bottom types, the Acroporaassociation on reef slopes and the coral patchThe living fauna of four sample groups are

distinct, with a few taxa and life habits characteriz- association, are not reflected by a distinct faunaof living molluscs, but are also included withining the composition (Figs. 5 and 7); only sample

group IV has a broad variety of taxa, reflecting sample group IV.The death assemblages in all five groups ofthe more heterogeneous character of samples

178 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

179M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

samples are dominated by the same taxa (mainly 1997a; Greenstein and Pandolfi, 1997). For thisreason it could well be that a future fossil mollus-Chamoidea, Spondylidae and Cerithium spp., in

different rankings) and the same life habits (mainly can assemblage is more similar to the original lifeassemblage than the present death assemblage isencrusters to dead hard substrata) (Fig. 7,

Table 6). Consequently, the ordination of dead to the present life assemblage (see Greenstein et al.,1998b for such an example among reef corals).molluscs does not reveal groupings that can be

related to specific hard substrata types (Fig. 6):here the results of the correspondence analysis 6.2. Taxonomic composition of live and dead

assemblagesexplain a few samples only, that are characterizedby exceptional faunal compositions (samples 4and 18). More than 68% of the live taxa are also found

dead on the hard substrata in our study area andA distinct distribution pattern of sample loca-tions with significant correlations of living and this percentage is greater than 94% if only those

taxa are considered that contribute at least 1% todead molluscs is recognized: seven sample loca-tions of sample group III are characterized by either the live or dead assemblage (reduced data

set). These values are similar to the mean valuesignificant correlation coefficients, but only one ofsample group II and none from sample groups I (87%) for non-reef molluscs of various sedimentary

environments ( Kidwell and Bosence, 1991). Theand V. From sample group IV, which contains thehighest number of sample locations (44), nine nearly 62% of dead taxa found alive in the study

area, which is distinctly above the mean valuesample locations show significant correlations ofliving and dead fauna. Of those, however, at least (44%) for non-reef molluscs of various sedimentary

environments ( Kidwell and Bosence, 1991),four mark a transition from sample group IV tosample group III, which is reflected in the distribu- increase to 100% when only the reduced data set

is considered.tion pattern of samples in Fig. 5.Including also data from molluscan death

assemblages in sediments from the same area(Zuschin, 1997) increases the proportion of live6. Discussiontaxa found dead to 79% for the complete data set,indicating that many individuals of hard substrata6.1. Sampling biastaxa are preserved in the adjoining sediment orwithin crevices of the coral framework. TheThe logistics of our sampling method provided

a strong bias against dead molluscs, that lived in remaining differences from non-reef molluscs ofvarious sedimentary environments can beclose association with living corals or coralline red

algae (bivalves of life habit group 1 in Table 3 and explained by preferential overgrowth of many mol-luscan taxa living in close association with a livingencrusting Dendropoma). Such molluscs are easily

overgrown after death and therefore we did not substrata. The comparatively high value of deadtaxa found alive can be related to the high percen-pick them with our sampling regime, but in fact

they have a very good chance of being incorporated tage of living individuals, which is in markedcontrast to results from studies dealing with mol-into the fossil record. Similar sampling biases are

also reported against massive corals in modern luscan assemblages in sediments ( Kidwell andBosence, 1991) and again points to preferentialdeath assemblages (Pandolfi and Greenstein,

Fig. 5. Ordination of samples and taxa and relationships between taxa and sites using the first three dimensions of the correspondenceanalysis on living molluscs. Points close to one another represent samples that are more similar in taxonomic composition than pointsfarther away from one another. Using dimensions 1 and 2 (A) shows sample groups (SG) I, II, III and IV established by (B)distribution pattern of living molluscs. Using dimensions 2 and 3 (C) shows sample groups (SG) II, III, IV and V established by(D) distribution pattern of living molluscs. #=Sample locations and taxa, $=sample locations with significant correlation coeffi-cients of living and dead fauna.

180 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Fig. 6. Ordination of samples and taxa and relationships between taxa and sites using the first three dimensions of the correspondenceanalysis on dead molluscs. Points close to one another represent samples that are more similar in taxonomic composition than pointsfarther away from one another. Using dimensions 1 and 2 (A) no sample groups were gained because (B) the distribution patternof dead molluscs is indistinct. Using dimensions 2 and 3 (C) again no sample groups were gained because (D) the distribution patternof dead molluscs is indistinct. Results of the correspondence analysis explain a few samples only, that are characterized by exceptionalfaunal compositions (samples 4 and 18). #=Sample locations and taxa, $=sample locations with significant correlation coefficientsof living and dead fauna.

181M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Table 6Molluscan composition of sample groups I–V, recognized by the correspondence analysis. Bold numbers are for dominant andcharacteristic taxa in sample groups

182 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Fig. 7. Assignment of molluscan life habits to sample groups shown by correspondence analysis.

overgrowth and transport into adjoining sediments 6.3. Abundances of taxa in live and deadassemblagesof the dead individuals.

The considerable increase of percentages whenconsidering only the reduced data set strongly In contrast to the good agreement between

living and dead molluscs regarding taxonomicsuggests that living taxa not found in the deathassemblage and dead taxa not found alive are composition, nearly all taxa that were abundant

as living individuals were rare as dead individualsquantitatively unimportant. This is supported bythe high percentage of dead individuals from taxa and vice versa: Pedum, Dendropoma, Coralliophila

and Tridacna are dominant in the living assem-found alive for the complete data set (Table 5).Comparisons with fidelity indices from reef blage, whereas Chamoidea, Spondylidae and ceri-

thiid gastropods are dominant in the deathcorals are difficult, because strong differences existbetween values from the Indo-Pacific and the assemblage. Generally, gastropods, which contri-

bute considerably to the total of living molluscs,Caribbean, which are related to diversity differ-ences, and between values from shallow and deep are very rare among dead molluscs on hard sub-

strata. This is in marked contrast to soft substrata,water studies, which are related to changes incommunity structure and/or differences in time where molluscan death assemblages consistently

show strong fidelity to relative abundances in theaveraging (Table 5) (Pandolfi and Greenstein,1997a). However, reef corals also have life histories live community ( Kidwell and Flessa, 1995;

Kidwell, in press).different from molluscs and are characterized byselective preservation of their taxa; these features Rapid post-mortem overgrowth of taxa that

live in close association with a living substratumare potentially responsible for observed differencesbetween fidelity indices of molluscs and reef corals (corals or coralline red algae) and post-mortem

transport of vagile fauna into surrounding sedi-in general (Pandolfi and Minchin, 1995).

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ments are considered to be the best explanations in the studied sediments, whereas contributions ofbivalves living in crevices of living or dead coralsfor the observed biased record of living and dead

molluscs. and boring into living corals are minor (Zuschinand Hohenegger, 1998).Additionally, hermit crab occupancy of empty

shells may be of some importance, but dead shellsof Coralliophila, which is the quantitatively most 6.4. Interactions of substrata and molluscan life

habitsimportant live vagile gastropod, are only found insediments around coral-dominated hard substrata(Zuschin and Hohenegger, 1998). Cerithium spp., Reef flats (sample group I ) are strongly domi-

nated by the encrusting gastropod Dendropomathe quantitatively most important dead gastropod,is found in the habitat of the living snails, despite maxima which lives cemented to dead hard sub-

strata or embedded into the tissue of living corals.frequent hermit crab occupancy. Therefore wewould rather exclude a major habitat anomaly due Obviously, these gastropods do not have a special

substrate preference, but require the agitated waterto hermit crab transport of shells, as for exampledescribed by Shimoyama (1979). Nevertheless, conditions on reef flats in order to spread their

mucous net for feeding (Hughes and Lewis, 1974).preferential hermit crab occupation of some gas-tropod taxa (compare also Frey, 1987) keeps their Such very high densities of these sessile gastropods,

however, are a phenomenon largely restricted todead shells in the original habitat for longer thanothers, producing an abundance anomaly (Walker, the Red Sea (compare Mastaller, 1978; Taylor and

Reid, 1984), with similar abundances only being1989) and being responsible for similarities/correlations of living and dead Cerithium spp. on reported from the SE Pacific (e.g. Salvat, 1971).

Despite the low proportion of living coral cover-rock grounds. However, distinct pagurization fea-tures like massive encrustations, alterations of the age, the very low abundance of dead individuals

can be explained by rapid overgrowth after death,aperture or pagurid facets (reviewed in Walker,1992 and Taylor, 1994) as found on a rocky especially as coralline red algae are very abundant.

Even with living Dendropoma usually only theintertidal in the Northern Bay of Safaga (Zuschinand Piller, 1997a) were never observed on the aperture of the animal can be recognized, as the

rest of the shell is already completely covered byinvestigated subtidal hard substrata. Only subtleencrustations of coralline red algae were obligatory coralline red algae or corals. Therefore on this

bottom type the similarity and correlation of livingon hermit crab inhabited shells of these environ-ments. Therefore recognition of hermit crab occu- and dead fauna is poor.

Sample group II, which represents most of thepancy of these shells in the fossil record would berather difficult. Porites-dominated reef slopes and coral carpets

(except sample location 21), is strongly dominatedAlternative possibilities for the observed biasare predatory loss of those taxa that settle within by molluscs with a close substrate relation to living

corals. Coralliophila and B. foliata are very typicalor in close association with living scleractinians ortheir taphonomic loss (see Murray and Alve, 1999 faunal elements, because they are nearly restricted

to this facies (Fig. 5). B. foliata has always beenfor an example of selective taphonomic loss amongforaminifera). However, no extensive predation on observed to live in crevices of living Porites spp.,

usually with direct contact between the bivalvethese taxa has been observed and the loss ofexactly those taxa that live in close association and the coral tissue. This is in contrast to Taylor

(1971), who reported this species from dead partswith a living substratum seems to be very unlikely.Our taphonomic interpretation is also supported of coral branches or massive corals. Coralliophila

violacea is a parasitic gastropod, that feeds onby a comparison with a detailed study on mollus-can death assemblages in sediments in the Porites and Porites (Synerea) (Robertson, 1970;

Schuhmacher, 1993). The low proportion of deadNorthern Bay of Safaga: the upper valves ofbivalves encrusting dead hard substrata and the individuals in this sample group again strongly

suggests rapid overgrowth of bivalves, which isshells of gastropods feeding on corals are abundant

184 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

supported by the high surface coverage by living can life habits to be developed on these bottomtypes (Fig. 7). Due to its intermediate positionscleractinians. Coralliophila is interpreted to fall

off after death and correspondingly will be found between sample groups II and III, two majortrends in the molluscan composition within thisin the surrounding sediments or in crevices between

coral heads. A comparison with a quantitative group can be recognized. Sample locations near tosample group II in the correspondence analysisstudy on molluscan death assemblages in sediments

confirms this view, as coralliophilids are an impor- are mainly characterized by molluscs with a dis-tinct relation to living corals. Streptopinna in mosttant faunal element in coral associated sedimentary

facies (Zuschin and Hohenegger, 1998). cases is embedded in living massive coral colonies,but sometimes is also found in crevices of deadAdditionally, those individuals that mainly con-

tribute to the dead fauna belong to encrusters of coral heads. The host-specific Pedum is associatedwith a variety of scleractinians (preferentiallysmall-sized dead hard substrata within the overall

living surface. These individuals take longer to be Montipora spp.) in the northern Red Sea( Kleemann, 1990). It occurs in living corals (e.g.overgrown than those that live in direct contact

with living corals. Therefore on this bottom type Yonge, 1967; Waller, 1972), where it lives as aborer and attaches byssally ( Kleemann, 1990).only one sample location (4) shows significant

correlations of living and dead fauna. Tridacna maxima is a coral reef-associated bivalve(e.g. Yonge, 1974), which is usually found byssallySample group III, which summarizes rock

grounds, contains many of those sample locations attached within or between living coral colonies.Sometimes penetration into the coral substratumwhich have a very high proportion of dead surface

and correspondingly a low coverage by living was obvious (compare Yonge, 1980). In a fewcases large, unattached specimens were found lyingscleractinians. Five samples from Sarcophyton car-

pets belong here and three sample locations from on the surface of reef slopes and coral carpets. Allof the mentioned taxa can also be found as abun-platy scleractinian carpets. Due to their high pro-

portion of dead surface, these bottoms are domi- dant constituents of sample group II, from whichthis assemblage mainly differs by the absence ofnated by Chamoidea, which have been observed

to colonize mainly bare rocky surfaces (Zuschin B. foliata and Coralliophila. Generally, these fea-tures suggest relatively high amounts of livingand Piller, 1997b,c). The second typical faunal

element is Cerithium spp. (C. echinatum, C. nodulo- surface, which increase towards sample group II.The somewhat strange coral composition of samplesum, C. ruppelli) which are well-known algal–

detritus feeders (Houbrick, 1992). Typically, after location 14 is reflected in the molluscan fauna andcorrespondingly a rather isolated position withindeath all this fauna remains at the surface of the

bottom for very long, as it will not easily be sample group IV.Sample locations near to sample group III areovergrown by corals or coralline red algae. In

accordance with this scenario, sample group III is characterized by bivalves that live as crevice dwell-ers within dead hard substrata, where they arethe only sample group strongly dominated by dead

individuals and characterized by consistent signifi- byssally attached (Barbatia setigera, Ctenoidesannulata, Isognomon legumen, Lima lima) (comparecant correlations and high similarities of living and

dead fauna. Hadfield, 1976; Morton, 1983a; Taylor, 1971). Inmost cases these hard substrata are dead coralSample group IV is the only sample group that

shows a very heterogeneous composition of bottom colonies or dead parts of otherwise living coralcolonies. A second important feature aretypes, molluscan taxa and molluscan life habits.

This is due to its intermediate position between Spondylidae and Ostreoidea, which are usuallyfound as encrusters on dead coral heads. Lophasample groups II, III and V (Fig. 5). More than

half of the sample locations, however, belong to cristagalli often produces striking clusters on uppervalves of spondylids, which themselves arecoral carpets with faviid or depauperate faviid

associations. The very high coral diversity (Riegl cemented to dead coral heads (Zuschin and Piller,1997b). Additionally Conus spp., which lives as aand Piller, 1997) enables a broad variety of mollus-

185M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

predator on a variety of invertebrates (e.g. Taylorand Reid, 1984) and whose favourable portions ofreefs have <20% cover of living coral (Kohn,1983), shows a relation to this facies. This faunareflects the low amount of living surface, whichdecreases towards sample group III in the corre-spondence analysis. Corresponding to the ratherlow coverage by living corals, the proportion ofdead individuals is relatively high on these bottomtypes. The interpretation of the importance ofovergrowth after death is supported on dead coralheads by the large proportion of dead crevicedwellers, which do not live in direct contact witha living surface. In correspondence to these obser-vations, four of eight sample locations with sig-nificant correlations of live and dead fauna on thisbottom type mark a transition to sample groupIII (rock grounds), but none is transitional tosample group II (Porites associations).

Sample group V represents most sample loca-tions of the Acropora–Millepora-dominated reefslopes (except sample location 27) and is domi-nated by molluscs with a close relation to livingcoelenterates: the typical Pteriidae (Electroma ala-corvi and Pteria spp.) are epizoic bivalves and notmuch is known about their habitat preferences(Oliver, 1992); we observed them byssally attached

A

Bto live branching corals (mostly Acropora) and the

Fig. 8. Recent and fossil Dendropoma: (A) living Dendropomahydrozoan Millepora. Drupella is a predator onin the Northern Bay of Safaga, scale bar=10 cm; (B) fossil

corals (Robertson, 1970; Schuhmacher, 1993) and Dendropoma from Pleistocene outcrops along the Red Seawas only encountered on Acroporans. Both taxa coast, scale bar=10 cm.are interpreted to fall off after death and thereforewill be found in the surrounding sediments. A the study area in general, and a dominance of live

fauna on all bottom types with a high proportioncomparison with quantitative bulk samples fromreef slopes confirms this view (Zuschin, unpub- of living surface (corals or coralline red algae). In

contrast, the only bottom type with a dominancelished material ). Therefore, on this bottom typeno significant correlations or high similarities of of dead individuals are rock grounds. We can

prove the fossil occurrence of molluscan taxaliving and dead fauna exist.within corals at least for Dendropoma maxima,which is a typical constituent of Pleistocene coralreefs along the Red Sea coast (Fig. 8).7. Palaeontological implications

Our interpretation also fits previous results,which show that coral reefs have a high temporalOur data indicate that most of the fauna living

in close association with a living hard substratum resolution and are well suited to preserve short-term fluctuations of the fauna due to the rapid(coral colonies and coralline red algae) should be

found embedded in the framework of fossil coral rates of reef growth compared with the aggrada-tion of soft sediments (Jackson, 1983; Crame,reefs. Our interpretation is supported by the high

proportion of live individuals on hard substrata in 1980, 1981).

186 M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

Therefore, the fauna rapidly overgrown by the high number of inner-reef specialists amongmolluscs, which are strongly affected by sea-levelliving substrata should provide considerable eco-

logical and temporal information. In contrast, the fluctuations (Paulay, 1990, 1996; Taviani, 1998).Finally, the fossil occurrence of the studiedfauna that colonizes dead hard substrata remains

much longer on the surface, indicated by the strong fauna depends on the preservation potential of therespective substrata, which may vary considerablydominance of dead individuals on rock grounds,

which mainly provide a dead surface. Con- due to the prevailing disintegrative processes anddiagenetic environments (for a review see Scoffin,sequently this fauna should be taphonomically

altered and considerably time averaged. 1992). For example, corals in higher energy envi-ronments may be less degraded than those fromTaphonomic alteration is obvious, as most dead

encrusting bivalves are disarticulated; time averag- lower energy, and fragile corals may be betterpreserved than robust coral growth forms due toing was not quantified. However, if this fauna

becomes entombed at their life sites, it may at least different residence times in the taphonomicallyactive zone (Pandolfi and Greenstein, 1997b).allow the study of faunal succession (Brett, 1988).

Fauna preferentially transported into surrounding The diagenetic history of uplifted Pleistoceneterraces along the northern Red Sea coast reflectssoft substrata will be affected by extensive time

averaging and taphonomic disintegration typically complex inter-relationships of climatic changes,sea-level variations of different orders, and tecton-occurring in soft sediments and the associated loss

of much ecological information (Flessa et al., ics and their diagenetic features are characterizedby a highly variable spatial distribution (Strasser1993; Flessa and Kowalewski, 1994; Fursich, 1978;

Fursich and Aberhan, 1990; Greenstein, 1989; et al., 1992; Strasser and Strohmenger, 1997). ThePleistocene coral reef faunas tend to be diageneti-Greenstein et al., 1995; Kidwell, 1998; Kidwell and

Bosence, 1991; Kowalewski, 1996; Kowalewski cally reduced in numbers compared with modernsediments from the same area. The reduction inet al., 1998; Meldahl et al., 1997; Olszewski, 1999;

Powell et al., 1989). diversity is due to widespread vadose diagenesis inthe Pleistocene sediments and is especially true ofHowever, the fossil occurrence of the studied

fauna will ultimately depend on the long-term aragonitic molluscs (Dullo, 1983, 1984, 1990). Thefaunal reduction increases with age of thestability of the studied assemblages as well as on

the preservation potential of the respective sub- Pleistocene terraces (Strasser et al., 1992; Strasserand Strohmenger, 1997) and only thick-shelledstrata. For reef corals, community structure is

stable in the long term (103–105 years) (Jackson, Tridacna and Strombus shells are well preserved,whereas smaller shells are not recorded (Dullo,1992; Jackson et al., 1996; Pandolfi, 1996, 1999).1984). The diagenetic environment seems toStudies in the Caribbean show that Pleistocenegovern shell preservation as the latter is very goodreefs exhibit excellent coral preservation and sig-(even primary coloration of molluscs is preserved)nificant similarities regarding taxonomy, zonationin uplifted terraces with slightly different climaticand diversity to living shallow water coral associa-factors and geological settings along the Red Seations (Mesolella, 1967; Greenstein and Curran,coast (Dullo, 1984).1997; Greenstein and Pandolfi, 1997; Pandolfi and

However, at least for the total species list, littleGreenstein, 1997a; Pandolfi and Jackson, 1997;differences exist between Pleistocene and modernGreenstein et al., 1998a). These Pleistocene reefsmolluscan assemblages from coral reefs of thecan even be used to calibrate an ecological baselineKenya coast (Crame, 1986; compare alsowith which to compare modern reef assemblagesValentine, 1989).(Greenstein et al., 1998a). In contrast, comparisons

of Pleistocene and modern molluscan assemblagesshow that significant faunal differences exist, which

8. Conclusionscan be related to significant habitat loss due toQuaternary sea-level fluctuations (Taylor, 1978;Crame, 1986; Paulay, 1996). These differences 1. Most taxa found dead in the study area were

also found live and vice versa; differences frombetween corals and molluscs might be related to

187M. Zuschin et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 159 (2000) 167–190

results on molluscan assemblages in sediments sediments from the same study area, observa-tions in Pleistocene deposits along the Red Seacan be related to the special accumulation con-

ditions of dead faunas on hard substrata. Living coast, and previous results, which show thatrapid reef growth is potentially suited to pre-taxa not found in the death assemblage and

dead taxa not found alive are proven to be serve ecological information.6. The approach of our investigation was to com-quantitatively unimportant.

2. Strong differences regarding dominating taxa bine the life habits of organisms with their post-mortem history. The fossil occurrence of theof living and dead molluscs are the result of

distinct biases in the death assemblage. Dead studied faunas, however, finally depends on thelong-term stability of the studied assemblagesmolluscs, that lived in close association with

living corals or coralline red algae, are strongly and on the preservation potential of the respec-tive substrata, which may vary considerablyunder-represented in the death assemblage.

Such molluscs are easily overgrown after death due to the prevailing disintegrative processesand diagenetic environments.and therefore were not recognized by our sam-

pling regime. These molluscs, however, have avery good chance of being incorporated intothe fossil record. Dead gastropods, that feed on

Acknowledgementscorals, are also strongly under-represented inthe studied death assemblage, because of rapid

Thanks are due to Abbas M. Mansour, Wernerpost-mortem transport into surrounding sedi-E. Piller, Michael Rasser and Bernhard Riegl forments or into crevices within corals.help with field work. Ronald Janssen, Eike3. Major similarities and significant correlationsNeubert and P. Graham Oliver helped with taxo-of living and dead faunas are mainly observednomic problems. Karl Kleemann, Werner E. Pilleron rock grounds, where the amount of scle-and Bernhard Riegl provided stimulating discus-ractinians can be neglected and encrustingsions on coral–mollusc interactions and the classi-Chamoidea dominate live and death assem-fication of hard substrata.blages. Similarities between living and dead

The authors are especially grateful to RobertCerithium spp. are influenced by hermit crabs,J. Stanton Jr., Susan M. Kidwell and reviewerswhich preferentially keep these shells in theirFranz T. Fursich and John M. Pandolfi, whosehabitat after death.comments improved the manuscript greatly.4. From a palaeoecological point of view the hard

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