Distributional overlap rather than habitat differentiation characterizes co-occurrence of bivalves in intertidal soft sediment systems

Abstract

Diverse species assemblages are often associated with a diversity of habitat structures. Sedimentary systems seem to be no exception, as within sedimentary systems benthic species diversity within a sample point appears to correlate with sediment grain size complexity. However, it remains to be shown whether total benthic species diversity relates to a system's sediment heterogeneity across multiple systems. In the present paper we examined whether bivalve diversity is associated with: (1) sediment heterogeneity across systems and (2) sediment grain size complexity within systems, at 9 temperate and tropical tidal flat systems. Although bivalve life-history strategies, like post-settlement habitat selection, might suggest that sediment heterogeneity should be important for bivalve species, bivalve diversity and sediment heterogeneity were not associated across systems. Interestingly, the association between total benthic diversity and sediment heterogeneity was also not significant, suggesting that changing species composition across systems does not account for the lack of a correlation between bivalve diversity and sediment heterogeneity. Instead of habitat differentiation, bivalve diversity within a sample point was highest in 'complex' fine-grained sediments and bivalve distributions showed a large degree of distributional overlap in all systems. The results of this study at both smaller and larger spatial scales suggest that coexistence between bivalve species in diverse tidal flats is not associated with increased sediment heterogeneity. (Orth et al. 1984, Edgar et al. 1994, Sheridan 1997, Boström et al. 2006, Honkoop et al. 2008) and sediment particle size diversity (Gray 1981, Whitlatch 1981, Etter & Grassle 1992.Within sedimentary systems, species richness within a sample point, i.e. point diversity, has been associated with sediment complexity (Whitlatch 1981, Etter & Grassle 1992, e.g. annelid diversity (Whitlatch 1981) and total benthic diversity in the deep sea (Etter & Grassle 1992) are correlated with fine-grained, 'complex' sediments. The association between species diversity and sediment grain size complexity has been suggested to reflect: (1) food diversity (Whitlatch 1981); (2) habitat complexity, as benthic species live on and within the sediment (Etter & Grassle 1992); (3) sediment particle size fractionation by numerous benthic deposit feeders (Etter & Grassle 1992); and (4) proximal factors like nutrient availability, hydrodynamics and microtopography (Etter & Grassle 1992). Interestingly, although causation cannot be implied, it has been suggested that diverse benthic assemblages may create diverse sediment characteristics (Etter & Grassle 1992).Across multiple systems, sediment heterogeneity of a system might be associated with diverse species assemblages because habitat 'niches' should be reflected by sediment heterogeneity (Snelgrove & Butman 1994) and benthic species can have distinct sediment preferences (Wolff 1973, van der Meer 1991, Ysebaert et al. 2002, Huxham & Richar...

Sampling bivalves on tidal flats: possibility of ­missing rare species, versus smoothing of ­environmental variation

“…Finally, although the Balgzand data-set, upon which the arguments of Beukema & Dekker (2011) are based, represent a unique collection, the spatial extent of the sampling is limited by comparison (Beukema et al 1983, Beukema & Cadée 1997 with the spatial distribution of samples in Compton et al (2008). Therefore, it is uncertain if the results from the Balgzand (Beukema & Dekker 2011) would be representative of the whole western Dutch Wadden Sea as shown in Compton et al (2008).…”

“…Thus, it is difficult to determine when environmental characteristics are similar enough to allow sample aggregation without resulting in under-or overestimation of species diversity. Our statistical regressions did not make assumptions about the homogeneity of habitat types and thus used many estimates of point diversity to show that bivalve diversity within a sample point was higher in finer versus sandier sediments across 9 mudflats (Compton et al 2008).…”

“…However, our main conclusion was based on a correlation between total system bivalve and benthic γ-diversity versus the range in sediment grain sizes for each system. The estimates of γ-diversity were determined using species accumulation curves for the whole system (see Compton et al 2008, their 'Materials and methods'). Our conclusion was also supported by boxplots of the raw data, which showed that the individual species overlapped in their distribution, with respect to median grain size, when comparing the different tidal flat systems (see boxplots in Compton et al 2008, their Fig.…”

“…ABSTRACT: Beukema & Dekker (2011;Mar Ecol Prog Ser 440:281−283) argue that the main conclusion of Compton et al (2008;Mar Ecol Prog Ser 373:25-35), namely that diversity of bivalve and other benthic organisms on tidal flats is not associated with sediment heterogeneity, is invalid because γ-diversity was not examined. Our conclusion was, however, based on γ-diversity.…”

Kimberley marine biota. History and environment

“…Another major contribution to knowledge of the North West Shelf coastal invertebrate fauna is an ongoing international study, coordinated by the Royal Netherlands Institute for Sea Research, on the vast mudfl ats of Roebuck Bay and Eighty Mile Beach in the Canning Bioregion (de Goeij et al 2003;Honkoop et al 2006;Pie rsma et al 2002Pie rsma et al , 2005aPie rsma et al , 2005bCompton et al 2008;Estrella et al 2011). These studi es were designed to p rovide understanding of the intertidal habitats and food resources of the large numbers of migratory shorebirds utilising these Ramsar Wetland mudfl ats.…”