Diversity and conservation of terrestrial arthropods in tidal marshes along the River Schelde: a gradient analysis Original Research Article

A large number of tidal marshes (in a gradient from fresh to salt water conditions) along the river Schelde (Belgium), were sampled with standardised effort during spring 1992. A total of 154 species of ground beetles, spiders, isopods and amphipods was recorded. Species richness was high in many large and small sites. Regression and DCCA analyses of these data indicate that the diversity of the fauna does not appear to be related to the area of the investigated sites but significantly increases from salt to freshwater conditions. The highest number of species, however, was recorded in some intermediate habitats, where brackish species, with high interest for conservation, co-occur with species of both saline and freshwater conditions. Many terrestrial arthropods respond clearly to the salinity gradient along this tidal river. Saltmarshes are highly differentiated from freshwater tidal marshes, due to the presence of several halophilic and halobiontic species or freshwater species, respectively. Other species prefer oligohaline habitats or show no response towards the salinity gradient. Secondary differentiation of terrestrial arthropod communities occurs along an ecological gradient from freshwater tidal marshes with litter accumulations to sites with barren soil, temporarily often with cracks. Despite the heavy pollution of the river Schelde, very rare arthropod species still survive in its tidal marshes. The observed communities are of high conservation interest, in a regional as well as in a larger west European context.