Functionally similar but taxonomically different: Benthic communities in 1889 and 2006 in an industrialized estuary

Abstract

Understanding shifts in benthic communities along gradients over time is of crucial importance in estuarine ecology and for conservation. Yet studies considering historical data and both taxonomic and functional aspects are rare. We analysed data of macrobenthic invertebrates of the highly modified Elbe Estuary (Germany) from 1889, 1985, 1986 and 2006 to assess community shifts and considered both taxonomic and functional aspects. The number of species, functional richness (FRic) and functional redundancy (FR) reached minimum values in 1985 and 1986 and were highest and similar in 1889 and 2006. However, beta-diversity analysis showed that species assemblages in 1889 and 2006 greatly differed, almost exclusively owing to species replacement. Most striking was the decline in gastropods after 1889 to levels approaching extinction in the estuary in the other sampling years, most likely due to elevated concentrations of chemical substances, such as tributyl tin. Functional beta diversity was mainly a result of functional nestedness and was exceptionally low in a comparison of data from 1889 to 2006, which indicated nearly complete functional recovery. Null models revealed that function loss in 1985 and 1986 was non-random, consistent with habitat filtering. All functional groups were present on all sampling dates, which suggested that FR might have provided protection from significant ecosystem function loss. Our results indicate that FRic and FR in 1889 could have promoted ecosystem resilience and stability.