Modern distribution of saltmarsh testate amoebae: regional variability of zonation and response to environmental variables

AbstractSea‐level reconstruction from biological indicators in saltmarsh sediments requires an understanding of the modern ecology of the organisms concerned. Previous work suggested that testate amoebae are a potential new group of organisms to use for sea‐level reconstruction, especially combined with diatoms and foraminifera. This paper analyses data from three saltmarshes on the Taf estuary, South Wales, the River Erme, Devon, and at Brancaster, Norfolk (UK) to (i) test for the presence and zonation of testate amoebae in relation to elevation; (ii) examine the similarity of zonation patterns between marshes; and (iii) explore the relationship between assemblage composition and a wider range of environmental variables. In addition we provide an update on the identification of testate amoebae on saltmarshes. Our results confirm that at all sites the primary environmental gradient is tidal inundation. Major changes in taxa along the tidal gradient are similar except for the lowest elevations, where different taxa become dominant at different sites. Canonical correspondence analysis (CCA) shows that assemblage composition is also strongly related to other variables, independent of the tidal position. Salinity, particle size and organic matter content are particularly important, and there is a statistically significant geographical effect on assemblages. Relationships between sea‐level and assemblage composition are often stronger for individual sites, suggesting that local data sets should be used for quantitative sea‐level reconstructions. However, the combined data set would provide more robust estimates of past sea‐level change from fossil data. Other environmental variables explain as much of the variability in species assemblages as tidal parameters and should be considered more often in sea‐level reconstructions based on microfossil indicators. Copyright © 2002 John Wiley & Sons, Ltd.