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

A large number of tidal marshes (in a gradient from fresh to salt water con ditions) along the river Schelde (Belgium), were sampled with standardised effort during spring 1992. A total of 154 species of ground beetles, spider s, isopods and amphipods was recorded. Species richness was high in many la rge and small sites. Regression and DCCA analyses of these data indicate th at 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 in termediate habitats, where brackish species, with high interest for conserv ation, 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 m arshes, due to the presence of several halophilic and halobiontic species o r freshwater species, respectively. Other species prefer oligohaline habita ts or show no response towards the salinity gradient. Secondary differentia tion of terrestrial arthropod communities occurs along an ecological gradie nt from freshwater tidal marshes with litter accumulations to sites with ba rren soil, temporarily often with cracks. Despite the heavy pollution of th e river Schelde, very rare arthropod species still survive in its tidal mar shes. The observed communities are of high conservation interest, in a regi onal as well as in a larger west European context. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.