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

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. Beu kema & Dekker (2011) also argue that our finding that bivalve point diversity was highest in 'complex' fine-grained sediments is incorrect, because small sampling areas underestimate rare species. Using larger sampling areas would have increased the probability of including rare species, but would also have smoothed away biological and environmental heterogeneity. We used many estimates of point diversity to show that bivalve diversity at a sampling point was higher in finer versus sandier sediments across 9 mudflats and we did not make assumptions about the homogeneity of habitat types. The suggestion that samples should be aggregated on the basis of similar environmental attributes across an area as large as the Wadden Sea would also lead to an under- or overestimation of species diversity because-although sampling locations may share the same sediment characteristics-species composition within a sample will differ due to historical, physical and biological effects. © 2011 Inter-Research.