Water mites as indicators of natural aquatic ecosystems of the coastal dunes of the Netherlands and northwestern France

Abstract

A large number of coastal dune waters in the Netherlands and northwestern France have been investigated for the occurrence of water mites. Dune waters turned out to be very rich in water mite species. In the Dutch dunes, 110 species of water mites have been found; this is 50 % of the total number of water mite species present in the Netherlands. In the French dunes 64 species have been found. The water mites most characteristic of the coastal dunes are the temporary water species. Dune areas with a high-lying hinterland have a water mite composition much different from dune areas with a low-lying hinterland. This can be explained by the existence of a very different hydrology. During the last century human activity affected the ground water of dunes. Afforestation and extraction of ground water for drinking water purposes caused a lowering of the ground water table. As a result, many dune slacks dried out. Moreover, the infiltration of river water caused an eutrophication of the ground water. Nowadays, the dunes most rich in typical water mite species are the dunes in which neither infiltration of river water nor extraction for drinking water purposes, occur. It can be concluded that water mites are good indicators for dune areas with a natural hydrology.