VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALT MARSH, SOUTH AFRICA

VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALTMARSH, SOUTH AFRICA

KATE L. STRACHAN1,3, TREVOR R. HILL

1, JEMMA M. FINCH1

AND ROBERT L. BARNETT2

ABSTRACT

Salt-marsh foraminifera are used as precise sea-levelchange indicators as surface assemblages vary in relation totheir position in the tidal frame. Surface-sediment sampleswere collected across an elevation gradient at Galpins saltmarsh, South Africa, to study the vertical distribution offoraminifera and their potential use for sea-level studies. Themarsh is divided into three vertical zones (high marsh, middlemarsh, and mud flats) represented by three assemblagegroups, with agglutinated species restricted to the upperreaches of the marsh and calcareous species more dominanttowards the intertidal channel. The high marsh area isdominated by Jadammina macrescens with a presence ofTrochammina inflata. The middle marsh is characterised byboth T. inflata and Miliammina fusca. Calcareous speciesfound in the mud flats consist of Haynesina germanica,Ammonia batava, and Quinqueloculina sp. This paperdescribes how marsh foraminifera can be used to definesmall-scale vertical zones along modern marsh surfaces andhow these zones correspond to floral zones. We demonstratethat marsh foraminifera have potential to be used as preciseindicators for sea-level reconstructions in South Africa.

INTRODUCTION

Modern foraminiferal assemblages form discrete verticalzones in salt marshes, strongly correlated with tidal levels(Scott et al., 2001; Gehrels & Newman, 2004). Therelationship between modern foraminiferal distributionand a range of environmental variables, including elevation,vegetation cover, pH, and salinity, can be preciselyquantified (e.g., using multivariate statistics), representinga modern analogue against which to compare fossilassemblages. Salt marshes experience daily and seasonalvariations in salinity and frequency of flooding linked totidal overflow. Several authors suggest that verticalzonation of foraminifera is strongly related to elevation,especially in temperate environments (Scott & Medioli,1980; Scott & Leckie, 1990; Horton & Edwards, 2003, 2006;Leorri et al., 2010).

It is well known that a variety of ecological controls exertan influence on the distribution of surface foraminifera(e.g., Murray, 1971; Scott et al., 1998; Horton, 1999),although assemblages are consistently shown to be verti-cally zoned in accordance with tidal frames, either directlyor indirectly (Berkeley et al., 2007). A study conducted inthe Great Marshes of Massachusetts by De Rijk &Troelstra (1997) found a strong correlation between high-

marsh foraminiferal distributions and salinity. The GreatMarshes are characterised by an irregular surface, provid-ing many local variations in elevation and salinity. Thus,elevational zonation directly linked to mean sea level (msl)is superseded by other gradients such as seepage of freshgroundwater and infiltration of seawater, especially in theupper reaches of the marsh (De Rijk & Troelstra, 1997).

By identifying the local vertical zonation of foraminiferaacross a marsh, establishing indicative meanings for specificassemblages (see Shennan, 2007), and applying these tofossil foraminifera preserved in a salt-marsh core, formersalt-marsh surface elevations, and thereby relative sea level,can be predicted (Gehrels, 1994; Horton & Edwards, 2006).Modern analogues of marsh foraminifera are traditionallycollected at the location where a sediment core is extractedfor palaeontological analysis (Gehrels, 1994; Kemp et al.,2009). Where assemblages are identified solely at a singlesite, some fossil samples may lack a modern analogue,thereby compromising the accuracy of the reconstruction(Murray, 2006). This lack of modern analogues could beaddressed by sampling a broader range of contemporaryenvironments (Hayward et al., 2004; Horton & Edwards,2006; Kemp et al., 2009).

Researchers have debated the best assemblage make-upfor foraminiferal population studies. Some advocate totalassemblage use, indicating environmental conditions forboth seasonal and temporal fluctuations (Scott et al., 2001;Horton et al., 2005). According to Murray (1971), livingpopulations best represent the modern environment as theuse of dead assemblages alone fails to account for post-mortem changes. However, it can be argued that thedistribution of living assemblages will be dependent on theconditions at time of sampling and not an average overtime. In temperate environments some suggest it isimportant to exclusively use dead assemblages as they arenot susceptible to seasonal variations, thus accuratelyreflecting subsurface assemblages (Murray, 1979; Hortonet al., 2005; Horton & Murray, 2007). On occasion, trainingsets comprised of total assemblages (live + dead) are stillused based on the assumption that live assemblages in timewill contribute to the fossil record (Booth et al., 2010). Astudy conducted on foraminiferal assemblages in surfacesediments from a marsh in Nova Scotia concluded thattotal foraminiferal assemblages provide a good basis forpalaeoenvironmental studies (Scott & Medioli, 1980).

Previous studies have described the distribution of salt-marsh foraminifera in temperate environments (e.g. Leorriet al., 2010). The highest intertidal zones are oftendominated by Jadammina macrescens and Trochamminainflata, which are replaced by species such as Haplophrag-moides sp. and Miliammina fusca as elevation decreases(Hawkes et al., 2010). Agglutinated species are prevalent inthe upper and middle marsh while calcareous species arescarce. This relationship depends on the accessibility of

1 Discipline of Geography, School of Agricultural, Earth andEnvironmental Sciences, University of KwaZulu-Natal, Private BagX01, Scottsville, 3209, South Africa

2 School of Geography, University of Plymouth, Plymouth PL48AA, United Kingdom

3 Correspondence author. E-mail: [email protected]

Journal of Foraminiferal Research, v. 45, no. 1, p. 29–41, January 2015

29

calcium carbonate within the environment (Leorri et al.,2010). Calcareous tests found in salt marshes with low pHare more susceptible to dissolution (Murray, 1971; de Rijk& Troelstra, 1997; Edwards & Horton, 2000). Therefore,calcareous tests may not be accurately represented insurface records with the more resistant agglutinatedforaminifera appearing more abundant (Edwards & Hor-ton, 2000). Living calcareous foraminifera in low pHenvironments show signs of dissolution (Hayward et al.,2004; Berkeley et al., 2007) after extended periods (Berkeleyet al., 2007). Ammonia becarii (Linnaeus) living in anenvironment with a pH of 7.0 became decalcified in 35 days,suggesting that pore-water conditions may prevent calcar-eous test accumulation (Le Cadre et al., 2003). In otherstudies, the preservation of agglutinated tests was reportedto be good in salt-marsh sediments (Scott & Medioli, 1982; deRijk, 1995). Taphonomic processes can result in a change inthe relative abundance of a particular species, thus modifyingthe composition of modern assemblages (Berkeley et al.,2007). The fossil foraminiferal assemblages of an intertidalenvironment are, therefore, the result of foraminiferalproduction, bioturbation, and taphonomic loss. To accurate-ly interpret a fossil record, it is important to understand theeffects of taphonomic loss and sediment reworking in adepositional environment (Berkeley et al., 2007).

Little has been published in South Africa regarding salt-marsh foraminiferal distribution in relation to tidal level.Franceschini et al. (2005) used salt-marsh foraminifera toinvestigate palaeoenvironments and palaeo-sea levels be-tween the late Pleistocene and Holocene on the west coastof South Africa, although limited information was providedregarding the distribution of modern foraminifera. Thishighlights the importance of establishing a detailed modernanalogue of foraminifera in a South African salt marsh,which can be used to quantify the relationship betweenmicrofauna and elevation in a local context.

The focus of this paper is to investigate the verticaldistribution of modern foraminifera in a South African saltmarsh to determine whether the assemblages show evidenceof vertical zonation. This paper tests whether foraminiferafrom this marsh can accurately predict salt-marsh surfaceelevations (Strachan et al., 2014), and thereby sea level, withprecisions comparable to that of published South Africansea-level studies by Siesser (1974), Miller et al. (1995),Marker (1997), Compton (2001), and Norstrom et al.(2012). In addition, we investigate whether dead foraminif-eral counts are more suitable for palaeo-reconstructionpurposes than total counts. The establishment of moderntraining sets of salt-marsh microfauna and a quantitativeinvestigation of their relationship with elevation is animportant first step towards the application of salt-marshmicroorganisms to reconstruct former relative sea levels inSouth Africa (Strachan et al., 2014).

STUDY SITE

Kariega Estuary, a permanently open, marine-dominatedsystem with little riverine influence, is located adjacent tothe town Kenton-on-Sea in the Eastern Cape, South Africa(Bate et al., 2004; Paterson et al., 2008; Fig. 1). Lowfreshwater influence is caused by the relatively arid climate

and the small catchment area regulated by three dams 50 kmupriver (Bate et al., 2004; Fig. 1D). The sinuous andelongated Kariega River channel varies in width from 40 min the upper reaches to 100 m in the lower estuary (Taylor &Allanson, 1995; Paterson & Whitfield, 2000a, b; Bate et al.,2004). The estuary stretches ,18 km inland and issurrounded by salt marshes, sand flats, and steep slopesas one moves upriver (Grange, 1992; Froneman, 2001).

Kariega has three main intertidal salt-marsh systems:Taylors, Grants, and Galpins. Grants and Taylors saltmarshes, both penetrated by shallow and narrow intertidalcreeks, are dominated by the marsh grass Sarcocorniaperennis (Mill.) A. J. Scott, whereas Galpins is dominatedby Spartina maritima (Curtis) Fernald and S. perennis(Paterson & Whitfield, 2000a, b). Galpins is attached to asmall estuarine embayment 5 km upstream from the mouthand protected from erosional dynamics associated with themain channel. It exhibits clear vegetation zones and itsintertidal creek is wider and deeper than those in the othertwo marshes (Whitfield & Harrison, 2003).

METHODS

FORAMINIFERAL SAMPLING, PROCESSING,AND IDENTIFICATION

Thirty-nine foraminiferal surface samples were collectedalong three elevational transects across Galpins salt marshin April 2010. Surface samples were collected at equalvertical intervals (,5 cm) and at marked changes in thefloral communities using a Pitman (10-cm diametercircular) handheld surface corer. Modern sediment sampleswere collected from three cross-marsh transects (Fig. 1C):Transect 1 (26 m), Transect 2 (32 m) and Transect 3 (7 m).Data from the three transects were combined to create atraining set of marsh and tidal-flat foraminifera. Thesamples were surveyed using a theodolite, backsited on afixed benchmark of known elevation, which was preciselylocated using a Leica GS20 differential GPS with externalantenna, relative to the TrigNet reference station atGrahamstown, South Africa. Sample elevations wererecorded as height above ellipsoid, which was then relatedto the local South African Geoid tidal datum using SouthAfrica Navy tide tables (South Africa Navy, 2011; Table 1).

Subsampling was conducted in the laboratory followingstandard practises (Gehrels, 2002). Subsamples of 4 cm3

were extracted from the top 1 cm of surface samples threedays after collection before degradation of the protoplasmcould occur. Remaining surface sediment was stored at 4uC.Each subsample was stained in a buffered Rose Bengal-ethanol solution, diluted with 20% distilled water (Scott &Medioli, 1980; Gehrels, 2002). Rose Bengal stains proteinwithin the foraminiferal cytoplasm and is used to distin-guish between live (stained) and dead specimens. Undercertain conditions the proteins degrade fairly slowly, andeven though metabolic activity has ceased, they can still bestained. In that way cytoplasm can be detected in the testsfor days or even months after death (Boltovskoy & Lena,1970). This could result in an overestimation of livingassemblages at the time of sampling (Schonfeld et al., 2012).However, protoplasm of living calcareous foraminifera can

30 STRACHAN AND OTHERS

degrade quickly depending on how the sample is storedbefore treatment, making it difficult to determine whichwere living at the time of collection (Horton & Edwards,2003). We assumed that foraminifera with stained proto-plasm in the last few chambers were living at time ofcollection (Horton & Edwards, 2003).

Subsamples were rinsed and washed through 63- and 500-mm sieves, removing coarse organic matter and detritus. The63–500-mm fraction was retained for foraminiferal analysisand subdivided into eight aliquots using a volumetric wet

splitter (Gehrels, 2002). The .500-mm fraction was disposedof once it had been viewed under the microscope to check forlarger foraminifera. Samples were kept wet during thecounting process to prevent aggregation of organic particlesand to minimise degradation.

A Leica M205C stereomicroscope was used for countingand identifying foraminiferal assemblages under 603, 803,and 1003 magnifications. A minimum of 250 specimens(live + dead) were counted per sample, a necessity whereindicator species are present in low numbers (Gehrels, 2002;Appendix 1). Several references (Murray, 1979; Horton &Edwards, 2006; Appendix 2) were used to aid in taxonomicidentifications of foraminifera found along the transects. Itwas only possible to identify Quinqueloculina and Fissurinato the genus level. Tests (including linings) that were eitherhighly fragmented or could not be identified weredesignated unknown.

Vegetation cover was identified along the transects, andplant species abundance recorded using a Braun-Blanquetscale (Poore, 1955). Species identification was aided usingLubke & de Moor (1998).

FIGURE 1. A Location map of Kariega Estuary, South Africa (33u419S, 26u429E). B The three main intertidal salt-marsh systems within theestuary (situated within box in D). C Transect locations on Galpins salt marsh. D Situation of Kariega Estuary in relation to neighbouringriver systems.

TABLE 1. Tide levels at Port Elizabeth relative to chart datum (CD;South Africa Navy, 2011).

Tide level Height (m CD)

Lowest Astronomical Tide 0Mean Low Water of Springs 0.21Mean Low Water of Neaps 0.79Mean Level 1.04Mean High Water of Neaps 1.29Mean High Water of Springs 1.86Highest Astronomical Tide 2.12

VERTICAL ZONATION SOUTH AFRICAN FORAMINIFERA 31

STATISTICAL ANALYSIS

Modern foraminiferal relative abundance was plotted aspercentages against elevation above Chart Datum (m aboveCD) using Psimpoll version 4.263 (Bennett, 2005). Con-strained Incremental Sum of Squares (CONISS; Grimm,1987) of total foraminiferal assemblage data defined threezones (K1, K2, and K3), which were used to assist ininterpretation of the modern foraminiferal assemblage datain relation to elevation. Data from the three surface transectswere compiled to form a training set of modern foraminiferalassemblages consisting of 37 samples (two samples on theterrestrial end of Transect 1 contained no foraminifera).Only a local training dataset was available for the area; thisdataset should be expanded in sample size and scale forfuture work. Training sets of dead and total assemblageswere compiled for ordination and regression modelling. Thisallowed us to test which dataset was most suitable forpalaeoenvironmental reconstruction. The relationship be-tween elevation and modern plant species was assessed usinga weighted averaging regression model in C2 (Juggins, 2003).This was used to determine elevational optima and toleranceranges for the salt-marsh flora. The relationship betweenelevation and modern foraminiferal assemblages was assess-ed using ordination and regression modelling of thepercentage counts. Canoco version 4.56 (Leps & Smilauer,2003) was used to run detrended canonical correspondenceanalysis (DCCA; ter Braak, 1985) to determine the eleva-tional gradient lengths of both modern foraminiferal trainingsets in terms of standard deviation units. The training setsboth exhibited short environmental gradient lengths of 1.3and 1.4 standard deviation units. Therefore, a partial leastsquares regression model was used in C2 (Juggins, 2003) tocalculate regression statistics, as is recommended for datasetswith gradient lengths shorter than two standard deviationunits (Birks, 1995). Prediction errors were calculated usingbootstrapping cross-validation at 1000 iterations.

RESULTS

VEGETATION

Galpins salt marsh exhibits upper and lower marshzonations based on the flora present along the surface

transects across the salt marsh. Generalised zonations (i.e.,high marsh, middle marsh, and tidal mud flats) are basedon Lubke & de Moor (1998). Taxonomic authority andnomenclature are based on Germishuizen & Meyer (2003).Approximately 70% of the marsh area can be described ashigh marsh, with this zone being denser in vegetationcompared to the lower sections of the marsh. The marsh isdominated by Sarcocornia perennis (high marsh), which ismore abundant than other plant species and has a modelledtolerance range of 1.4–1.8 m above CD (Fig. 2). Thehighest reaches of the intertidal zone, closest to theterrestrial edge, are occupied by Carpobrotus edulis (L.) L.Bolus and Sporobolus virginicus (L.) Kunth, species whichare normally associated with the high-marsh zone. Thesespecies have a modelled range of 1.7–2.4 m above CD. Thehigh-marsh zone is dominated by Bassia diffusa (Thunb.)Kuntze, Sarcocornia perennis, and Limonium linifolium(L.f.) Kuntze with less frequent occurrence of Triglochinstriata Ruiz & Pav. The lower marsh predominantlycontains Spartina maritima and Zostera capensis Setch.,both of which extend onto the tidal mud flats.

SALT-MARSH FORAMINIFERA

Thirteen taxa were identified across the Galpins saltmarsh in the Kariega Estuary, seven of which wereagglutinated forms (Fig. 3). Foraminifera were abundantand well-preserved, with the exception of two surfacesamples on the extreme terrestrial edge, which contained noforaminifera. The relative abundance of live (Fig. 3A) anddead (Fig. 3B) foraminifera are described collectively asthese datasets show close correspondence; exceptions aredescribed where applicable.

Constrained cluster analysis (CONISS) identified a high-marsh zone (K1) dominated by Jadammina macrescens andcontaining a lower percentage of Trochammina inflata.Miliammina fusca is the only other form that occurs in thiszone, albeit in low percentages. Zone K1 extends from1.95–2.05 m above CD, representing a narrow verticalniche, containing a very specific foraminiferal assemblage.

Three species dominate zone K2, which ranges from 1.4–1.95 m above CD. The abundance of the agglutinatedspecies J. macrescens and T. inflata decreases with

FIGURE 2. Optimal elevational tolerance of salt-marsh vegetation at Galpins salt marsh. N is the number of occurrences along the master transectand each black dot represents the midpoint of the range of tolerance for each species.


decreasing elevation. Conversely, the abundance of M.fusca increases with decreasing elevation. Trochamminaochracea represents a minor agglutinated species thatoccurs in this middle part of the marsh. This species onlyoccurs between 1.35–1.75 m above CD and thus mayrepresent an important sea-level indicator. Calcareousspecies are rare within this zone, although species ofAmmonia, Fissurina, and Quinqueloculina occur on occasionin very low percentages.

CONISS bounded the lowest zone K3 between 1.1–1.4 mabove CD, and although the upper part of the marsh wassampled until no foraminifera were present, the lowersampling boundary did not extend beyond the low marshand tidal mud flats. Samples from these elevations containa higher percentage of calcareous species, in particularspecies of Quinqueloculina, and a much lower percentage ofJ. macrescens and T. inflata. Zone K3 is largely dominatedby M. fusca, which dominates samples from theseelevations.

The relative abundance of dead foraminifera shows closeresemblance with the live counts of the same species, with

the slight exception of dead counts for J. macrescens, whichincrease relatively early in zone K2 and continue to increase

with elevation towards the terrestrial edge. In contrast, liveJ. macrescens peak at 1.8–1.9 m relative to CD and thenrapidly decline into zone K1. As a rule, samples contain

similar numbers of both live and dead tests across thedataset, and both crops of foraminifera exhibit the

successional trends described above. These are importantfor sea-level studies as the fossilised collections of forami-

nifera must reliably reflect the environment they weredeposited in. Similar crops of stained and unstained testsimply that the fossil record is likely to contain assemblagesindicative of their original environment.

ELEVATION RELATIONSHIPS OF FORAMINIFERA:

The visual distribution of modern foraminifera (Fig. 3)suggests that species are responding, at least in part, tochanges in elevation. Regression modelling was used tofurther assess this relationship. Sample elevations of twomodern training sets (dead and total) were predicted usingpartial least squares (PLS) models. Comparison of model-predicted elevations and the field-surveyed sample eleva-tions demonstrate the strength of the model and the abilityof the proxy to accurately predict salt-marsh surfaceelevations based on foraminiferal assemblages alone.

In both instances, the PLS model with two componentsproduced the best results in terms of sample-elevation-prediction accuracies using root mean squared error ofprediction (RMSEP) and r2

(boot) as the performance criteria(Table 2). A low RMSEP suggests that the model is capableof estimating salt-marsh surface elevations with lowuncertainties. The negative percentage change in RMSEPfrom using PLS with a third component suggests this modelmay be artificially improving the data fit and should,therefore, be discounted (Birks, 1998). The modelled sampleelevations are presented with the surveyed elevations for thetraining set comprised of dead counts only (Fig. 4A). Thecoefficient of determination [r2

(boot) 5 0.64] implies there isa reasonably strong relationship between the observed and

FIGURE 3. A frequency histogram of the distribution of live (A) and dead (B) modern foraminifera across Galpins salt marsh, Kariega Estuary.Zonations are based on CONISS.


modelled sample elevations. Samples from the higherreaches of the marsh have their elevations predicted mostaccurately. The four highest samples have the lowest modelresiduals, suggesting these dead-assemblage counts areunique across the marsh and occupy a narrow elevationalniche (Fig. 4B). Using a PLS regression model with twocomponents and bootstrapping cross-validation, the mod-ern training set composed of dead assemblage counts is ableto predict marsh elevations to precisions of 6 17 cm(RMSEP 5 0.17).

In comparison, the training set compiled of total (live +dead) foraminiferal counts performs almost equally well(Figs. 4C, D). The coefficient of determination againindicates good correlation between observed and surveyedsample elevations [r2

(boot) 5 0.64], and the PLS model withtwo components has equal prediction capabilities (RMSEP5 0.17). In contrast, the training set of total counts appearsto predict sample elevations from across the marsh equallywell. Samples from the higher reaches do not contain thelowest model residuals, unlike the former model. This islikely driven by the assemblage characteristics. There ismore change shown by the dominant species J. macrescensacross the marsh in the dead assemblage counts than in thetotal. Indeed, in the highest samples, dead counts of J.macrescens are at their highest (.60%), where, in compar-ison, the live counts are low (,20%). This suggests seasonalbias in the foraminiferal sampling and the effects this mayhave on training sets and models based on counts thatinclude living populations. The model comparisons, there-fore, advocate the use of dead assemblages only whenconstructing a training set of modern assemblages.

DISCUSSION

This study was designed to assess how well foraminiferaare able to predict surface elevations in a South African saltmarsh. The results from Galpins salt marsh suggest thatforaminiferal assemblages exhibit evidence of verticalzonation. The distribution of foraminiferal assemblagesacross the surface of the intertidal zone is, therefore, used asa proxy for elevation, though the duration and frequency ofintertidal exposure must be considered as these factors alsoaffect species distribution (Scott & Medioli, 1978; Jenningset al., 1995; Franceschini et al., 2005).

The relationship between salt-marsh foraminifera andelevation above CD often correlates with salt-marshvegetation. Many salt marshes exhibit distinct plantzonations, which are controlled by tolerance to tidal

inundation, competition (Gehrels, 1994), and environmen-tal factors, such as elevation and salinity (Horton, 1999),making them useful to sea-level research (Jennings et al.,1995; Horton, 1999). Three vegetation zones can beidentified at Galpins salt marsh using the relative abun-dance of the dominant plants: mud flats, low marsh, andhigh marsh (Jennings et al., 1995). Galpins’ mud-flat zonecorresponds with that identified by Lubke & de Moor(1998). The mud flats are colonised by Zostera capensis,followed by a low-marsh zone stabilised by Spartinamaritima in shallower water (Lubke & de Moor, 1998).The low-marsh zone is situated between the low-water markand neap tide or high-water mark (Gehrels, 1994). Thehigh-marsh zone can be subdivided into the upperSporobolus virginicus zone and the lower Bassia diffusa-Sarcocornia perennis-Limonium linifolium zone.

At Galpins, the plant zonation suggests that both thetidal mud flats and the lower-marsh zones are relativelynarrow; the majority of the marsh is classified as highmarsh, similar to that of the Kowie and Swartkops rivers inthe Eastern Cape, South Africa (Lubke & de Moor, 1998).Limonium linifolium indicates a middle-marsh zone; how-ever, this species is dispersed throughout the marsh, andthere is little evidence of middle-marsh vegetation (Lubke &de Moor, 1998).

Salt-marsh plant zonation at Galpins is similar to earlierobservations of the transitional zones indicated by surfaceforaminiferal assemblages. However, there are some impor-tant differences. The foraminiferal high-marsh zone coincideswith the high-marsh vegetation zone, as seen at Langebaan,South Africa (Franceschini et al., 2005) and in the NorthernHemisphere (Scott & Medioli, 1978; Gehrels, 1994; Jenningset al., 1995; Horton, 1999). The low-marsh zone, as identifiedby foraminiferal assemblages, approximately coincides withthe low-marsh vegetation zone. The transition zone betweenhigh and low marsh is characterised by a decrease in T. inflataand an increase in M. fusca (Horton & Edwards, 2003).However, the transition between the high and low marsh, asdemarcated by the foraminifera, is further away from theintertidal channel as compared with the distribution of thelow-marsh species Spartina maritima (Gehrels, 1994; Jenningset al., 1995). Scott and Medioli (1978), Patterson (1990),Gehrels (1994), and Horton (1999) found low-marsh floralzones to be dominated by M. fusca with low numbers of H.germanica, concordant with the findings of this research.

Modern foraminiferal training sets are applied to down-core fossilised assemblages via a transfer function toreconstruct palaeomarsh surface elevations and, thereby,

TABLE 2. Performance of the partial least squares (PLS) in terms of sample-elevation-prediction accuracies.

RMSEP (m) r2 RMSEP (m) r2 (boot) % change (RMSEP)

Dead crop

PLS 1 0.19 0.51 0.22 0.45 n/aPLS 2 0.15 0.71 0.17 0.64 21.67PLS 3 0.13 0.76 0.17 0.65 20.83

Total crop

PLS 1 0.16 0.66 0.18 0.61 n/aPLS 2 0.15 0.70 0.17 0.64 1.19PLS 3 0.14 0.75 0.19 0.62 PLS 4


relative sea level (e.g., Barlow et al., 2013; Strachan et al.,2014). Franceschini et al. (2005) represent one of the fewstudies to successfully reconstruct relative sea level in SouthAfrica using, in part, foraminifera. Our study encounteredsimilar marsh species and successional patterns describedfor Langebaan Lagoon by Franceschini et al. (2005). Bothlocations contain a high diversity of calcareous species atthe lowest marsh elevations and the middle-marsh zone ischaracterised by T. inflata and J. macrescens. The highmarsh at Galpins salt marsh is identified by the dominanceof J. macrescens, whereas at Langebaan the highestelevations are occupied by T. inflata alone. The similarities

seen between studies from opposite coastlines of SouthAfrica, the reconstruction attempts by Franceschini et al.(2005), and the model precisions shown here suggest thatsalt-marsh foraminifera from South African marshes maybe capable of predicting palaeomarsh surface elevationsand thereby reconstruct relative sea levels to precisionsunprecedented in previous South African sea-level studies.

Compton (2001) used salt-marsh foraminifera withinsediment cores from Langebaan to identify salt-marshfacies which provided an indicative range measured fromthe modern environment. Identification of the facies aloneprovided an indicative range of 0–1 m above msl (Compton

FIGURE 4. Modelled sample elevations regressed with the surveyed elevations and residual plots for dead assemblages only (A, B) and total (living+ dead) assemblages (C, D). Both dead and total assemblages have an r2 value of 0.64.


& Franceschini, 2005). By performing an analysis of themodern environment and developing a modern training set,the indicative ranges of salt-marsh indicators can benarrowed. Shennan (2007) provides a summary of hownarrow vertical niches occupied by specific assemblages ofsalt-marsh foraminifera can be used to provide tightlyconstrained indicative meanings. The higher-elevationassemblages presented here suggest that a sample composedof J. macrescens (80–100%) and T. inflata (0–20%), with acomplete absence of M. fusca, could have an indicativemeaning of 2.05 6 0.05 m above CD. Salt-marsh studiesthat use foraminifera as a sea-level-indicating proxy providethe opportunity to accurately reconstruct relative sea-levelhistories beyond the length of tide-gauge records withappropriate consideration for reconstruction uncertainties,which are not always accounted for.

Salt-marsh foraminiferal characteristics from Galpinsmarsh, Kariega, share similarities with studies beyondSouth Africa. Jadammina macrescens is typically found inthe highest parts of the intertidal zone with abundancedeclining towards the intertidal channel (Gehrels & van dePlassche, 1999; Sen Gupta, 2003; Horton & Edwards,2006). Galpins salt marsh contained a small number of T.inflata in the high-marsh zone. A study conducted at FraserRiver delta in British Columbia (Canada) identified T.inflata as a high- and middle-marsh species, co-dominatingwith J. macrescens (Williams, 1989; Patterson, 1990). Theco-occurrence of these two species was observed at Galpinssalt marsh and Langebaan Lagoon salt marsh, South Africa(Franceschini et al., 2005). Miliammina fusca and T. inflataoccur with one another in vegetated marshes worldwide(Scott & Medioli, 1978; Berkeley et al., 2007). Aninvestigation at Cowpens marsh in England suggested thetransition between high and low marsh is characterised by adecrease in T. inflata and an increase in M. fusca (Horton &Edwards, 2003). This trend is evident at Galpins, withincreasing abundance of M. fusca and decreasing abun-dance of T. inflata, as elevation decreases.

The percentage decrease of agglutinated species andincrease of calcareous species correspond with the transi-tion between low marsh and tidal mud flats (Horton &Edwards, 2006) at Galpins. Similar studies from Europe,North America, and Langebaan identify highest foraminif-eral diversity in the mud flats (Patterson, 1990; Horton,1999; Franceschini et al., 2005). The Galpins salt-marshtransition zone between low marsh and high marsh ischaracterised by a rapid decrease in T. inflata, replaced byH. germanica and Ammonia species. This tendency isevident at Langebaan (Compton, 2001) and at Cowpensmarsh (Horton & Edwards, 2003). Species of Haynesinaand Ammonia populate the lower tidal zones (Berkeleyet al., 2007).

The similarities with marshes worldwide imply thatfuture South African studies may lead to relative sea-levelreconstructions of comparable precision (i.e., 6 5–20 cm;Gehrels & Woodworth, 2013). It would be prudent,however, to investigate ecological controls on SouthAfrican salt-marsh foraminifera prior to reconstructionattempts, as this area of research is severely lacking in thecountry. Combining floral and foraminiferal verticalzonation across salt marshes in South Africa may help to

further reduce uncertainties in future studies concernedwith relative sea-level reconstruction (Strachan et al., 2014).

SUMMARY AND CONCLUSIONS

Foraminiferal assemblages from Galpins salt marsh in theKariega Estuary exhibit a clear vertical zonation resemblingthat found in salt marshes along the west coast of SouthAfrica and in the Northern Hemisphere. Three salt-marshzones were identified through changes in foraminiferalassemblages. The high marsh is dominated by J. macrescenswith a low abundance of T. inflata. The middle marsh ischaracterised by a higher presence of T. inflata, a lowerabundance of J. macrescens, and significant occurrence of M.fusca. The lowest zone contains the calcareous species H.germanica, A. batava, and Quinqueloculina sp., while thehighest zone contains more agglutinated species. Regressionmodelling of the modern training set suggests salt-marshforaminifera are able to predict marsh surface elevationswith a precision of 6 17 cm, comparable to published salt-marsh based sea-level studies. Sea-level research in SouthAfrica should use the local resources available to providehigh-precision and high-resolution reconstructions of recentsea-level change (e.g., Strachan et al., 2014), previously notapplied in the country. Suitable salt marshes have beenidentified throughout the coastal zones of South Africa andfurther analysis of modern day microfaunal assemblages andsubsurface litho- and biostratigraphies should be able toproduce relative sea-level reconstructions comparable withthose published worldwide.

ACKNOWLEDGEMENTS

This research was financially supported by the NationalResearch Foundation (NRF). Angus Paterson (SAEON)facilitated access to the study site. Martin Hill and JulieCoetzee (Rhodes University) assisted in fieldwork. JussiBaade (University of Jena) assisted with GPS data. BriceGijsbertsen (UKZN) professionally drafted Figure 1. Weare thankful to three anonymous reviewers for providinguseful comments on the manuscript.

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Received 24 October 2013Accepted 19 March 2014


APPENDIX 1

Raw foraminiferal counts.


APPENDIX 2

Taxonomic species list. In this appendix we describe the dominantagglutinated and calcareous foraminifera found in surface sedi-ments from Galpins salt marsh, Kariega, South Africa. Theagglutinated foraminifera characterise the vegetated marsh surface,while the calcareous species dominate the intertidal mud flats.Besides describing their features, a summary of their distribution isprovided.

Suborder TEXTULARINA Defrance, 1824Scherochorella moniliformis (Siddall, 1886)

Reophax moniliforme Siddall, 1886, p. 54, pl. 1, fig. 2; Haynes, 1973,p. 24, pl. 3, fig. 17, pl. 6, fig. 8.

Description. The test walls are agglutinated and pale brown. Theyare made up of tiny detrital grains held together in an organic cement.Scherochorella moniliformis is cylindrical and uniserial, with a terminalaperture (Murray, 1979; Horton & Edwards, 2006). Its average lengthis 0.8 mm (Murray, 1979).

Distribution. This is a sediment-dwelling, essentially marine speciesfound usually on the inner shelf or occasionally in estuary mouths(Murray, 1979).

Miliammina fusca (Brady, 1870)

Quinqueloculina fusca Brady in Brady & Robertson, 1870, p. 47, pl. 11,figs. 2, 3.

Description. Agglutinated test walls are composed of sand-sizeddetrital grains, held together by pale-brown organic cement. However,form and structure will vary slightly with grain size. The test is made upof many chambers coiled on a milioline plan; it is elongated androunded in section. Aperture terminal with a tooth (Murray, 1979;Horton & Edwards, 2006). Average length of 0.4 mm (Murray, 1979).

Distribution. Miliammina fusca is a sediment-dwelling euryhalinespecies, and is restricted to a narrow elevation zone within brackishlagoons, estuaries, and tidal marshes (Murray, 1979; Horton &Edwards, 2006). This species was found in abundance in the intertidalchannels at Kariega Estuary.

Trochammina ochracea (Williamson, 1858)

Rotalina ochracea Williamson, 1858, p. 55, pl. iv, fig. 112, pl. v, fig. 113.

Trochammina ochracea (Williamson). Balkwill & Millett, 1884, p. 25,pl. J, fig. 7.

Description. Trochammina ochracea has aggultinated walls made upof very fine detritus in organic cement. The test appears reddish brown.It is trochospirally coiled, very compressed with acute periphery, andusually has a maximum diameter of 0.2 mm (Murray, 1979). Thespiral-side structure is slightly depressed and curved backwards.

Distribution. Trochammina ochracea is an inner shelf species andspend its life clinging to pebbles and seaweed (Murray, 1979).

Trochammina inflata (Montagu, 1808)

Nautilus inflatus Montagu, 1808, p. 81, pl. 18, fig. 3.

Trochammina inflata (Montagu). Bronnimann and Whittaker, 1984,p. 311–315, figs. 1–11.

Description. Agglutinated test is composed of very fine detritalgrains with the outer layer being brown organic cement. The test istrochospirally coiled with globular chambers. The sutures are gentlydepressed on the spiral side and deeply depressed between the inflatedchambers on the umbilical side. The aperture is a narrow slit withbordering lip. The average size is 0.4 mm in diameter (Murray, 1979;Horton & Edwards, 2006).

Distribution. Trochammina inflata is a sediment-dwelling species,commonly found in higher elevation zones within salt marshes. Ittypically can survive in stressful environments, including those withperiodic low-oxygen levels (Murray, 1979).

Jadammina macrescens (Brady, 1870)

Trochammina inflata (Montagu) var. macrescens Brady in Brady &Robertson, 1870, p. 47, pl. 11, figs. 5 a–c.

Description. Agglutinated test made up of incredibly fine detritalgrains held together by brown organic cement. The walls areparticularly thin and flexible when wet; however, chambers tend tocollapse when dry. The test is trochospirally coiled and compressedwith a shallow umbilicus (Murray, 1979; Horton & Edwards, 2006).The sutures are slightly raised when the chambers collapse (Murray,1979). The aperture is a slit at the bottom of the apertural face withareal pores spread across the face. The average diameter is 0.3 mm(Murray, 1979; Horton & Edwards, 2006).

Distribution. Jadammina macrescens is one of the most abundantspecies found worldwide in brackish marshes and is able to surviveextreme environmental conditions (Murray, 1979). At Kariega, thisspecies was recorded in abundance in the high marsh.

Textularia earlandi Parker, 1952

Textularia earlandi Parker, 1952, p. 458, n. name for Textulariatenuissima Earland, 1933, p. 95, pl. iii, figs. 21–30 [preoccupied].

Description. The test is agglutinated and the chambers are biseriallyarranged and laterally compressed. The aperture at the base of the lastchamber is a simple arch (Scott et al., 2001).

Distribution. This species is found in most coastal environments;however, it is usually not the dominant taxon.

Suborder MILIOLINA Williamson, 1858Quinqueloculina sp.

Description. The tests are porcellaneous with a translucent toopaque appearance. The chambers are coiled on a quinqueloculineplan, with terminal aperture, usually with a tooth (Murray, 1979;Horton & Edwards, 2006). Quinqueloculina has an average length of0.3 mm (Horton & Edwards, 2006).

Distribution. Quinqueloculina are sediment dwelling and colonisemouths of estuaries if the conditions are favourable. They are alsocommonly found in the inner shelf as well as middle/low marshes andtidal flats (Horton & Edwards, 2006).

Suborder ROTALIINA Delage and Herouard, 1896Ammonia batava (Hofker, 1951)

Streblus batavus Hofker, 1951, p. 498, text–figs. 340, 341.

Ammonia batavus (Hofker). Haynes, 1973, p. 187, pl. 18, figs. 5, 6, 14,16, text–fig. 39:1–4.

Description. The test of A. batava is calcitic with radially arrangedcrystallites and pores, and appears glassy, translucent, and brownish incolour. It generally has a flattened dorsal side with a subangular tosubrounded periphery. Eight to nine chambers are common on theventral side (Horton & Edwards, 2006).

Distribution. Specimens of Ammonia batava are commonly found inlow-marsh and tidal-flat environments (Horton & Edwards, 2006;personal observation), and occasionally occur in high abundance(Horton & Edwards, 2006).

Ammonia aberdoveyensis Haynes, 1973

Ammonia aberdoveyensis Haynes, 1973, p. 184, pl. 18, fig. 15, text–fig.38: 1–7.

Discussion and distribution. This species differs from A. batava inlacking an umbilical boss. It also has eight to nine rather than six toeight chambers per spiral (Murray, 1979). In Kariega, this species wasfound in low-marsh and tidal-flat environments.

Ammonia tepida (Cushman, 1926)

Rotalia beccarii (Linnaeus) var. tepida Cushman, 1926, p. 79, pl. 1, figs.8a–c.

Discussion. This species is similar to A. aberdoveyensis; however, ithas slightly fewer chambers per whorl (Murray, 1979).

Spirillina vivipara Ehrenberg, 1843

Spirillina vivipara Ehrenberg, 1843, p. 422, pl. 3, fig. 41, sec. 7.


Description. The test of S. vivipara has a calcite wall that behavesoptically as a single crystal and appears glassy with pores. It isplanispirally coiled, compressed, and composed of a long, undividedtubular chamber following the proloculus. The aperture is simple. Thegreatest test diameter is 0.1 mm (Murray, 1979).

Distribution. Spirillina vivipara is a marine species found along theinner shelf. It clings to solid structures, such as pebbles and seaweed.It occasionally is found in estuary mouths (Murray, 1979).

Fissurina sp.

Description. Generally the walls of Fissurina are composed ofradially arranged calcite crystallites, with very fine, translucentpores. The single-chambered test is oval in shape. The aperture is alenticular peripheral slit with an entoselenian tube that extends intothe chamber of the test. Ornamentation consists of peripheralthickening or translucent to opaque bands (Murray, 1979).

Distribution. The genus is commonly found along marine shelves onmuddy substrates. However, empty tests can be transported intoestuarine systems and deposited in mud (Murray, 1979).

Haynesina germanica (Ehrenberg, 1840)

Nonionina germanica Ehrenberg, 1840a, p. 23 [figured in Ehrenberg,1840b, pl. 2, figs. 1a–g].

Protelphidium anglicum Murray, 1965, p. 149–150, pl. 25, figs. 1–5, pl.26, figs. 1–6.

Haynesina germanica (Ehrenberg). Banner & Culver, 1978, p. 191, pl. 4,figs. 1–6, pl. 5, figs. 1–8, pl. 6, figs. 1–7, pl. 7, figs. 1–6, pl. 8, figs. 1–10, pl. 9, figs. 1–11, 15 18.

Description. Haynesina germanica has a finely perforated, calcitictest with radially arranged crystallites. It appears glassy and isplanispirally coiled with five to 11 chambers. The aperture consistsof a row of pores at the base of the last chamber (Horton & Edwards,2006).

Distribution. Haynesina germanica is a common marsh species,where it is the most abundant calcareous species. Even though it isfound in middle and low marshes, H. germanica is found dominantly intidal flats (Horton & Edwards, 2006).


VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALT MARSH, SOUTH AFRICA

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