The Contrasting Ecology of Free-Living Nematodes in Macrotidal and Microtidal Estuaries

Abstract

This paper compares the diversity, distribution and trophic composition of the nematode assemblages in the intertidal sediments of the macrotidal Exe Estuary (UK) and the shallow subtidal sediments of the microtidal Swan Estuary (Australia), the latter having been subjected to long-standing anthropogenic disturbance. Data from studies partially described in earlier papers are analysed in a novel comparative way to demonstrate that any differences are attributable to the effects of their contrasting tidal regimes and not to levels of anthropogenic disturbance. They will thus have generic applicability to other macrotidal and microtidal estuaries and to taxa other than nematodes. Although nematode taxonomic and trophic α diversity in the two estuaries are similar, β diversity and consequently γ diversity are much higher in the Exe as a result of the greater heterogeneity of its benthic habitats. In the Exe, there is a gradual transition in taxonomic composition from the estuary to the coast, whereas the composition within the Swan is more uniform and contrasts sharply with that of the coast. Taxonomic and trophic composition correlate closely with sediment environmental variables in the Exe but not the Swan, in which physico-chemical properties of the overlying water are more important. Significant differences between the nematode faunas in the two estuaries result principally from the relatively greater importance of predatory families in the Exe and of deposit-feeding families in the Swan. Nematode diversity is greater than that of the macrobenthos in both estuaries, and this may be true for other naturally disturbed shallow water environments. The lack of faunistic heterogeneity in microtidal estuaries may account for their relative lack of resilience to anthropogenic disturbances and climate change.