De Molluskenfauna van Zuidoost Walcheren, speciaal met betrekking tot het natuurreservaat Rammekenshoek

THE LAND MOLLUSCA OF SOUTHEASTERN WALCHEREN WITH SPECIAL REFERENCE TO THE NATURE RESERVE RAMMEKENSHOEK The Nature Reserve of Rammekenshoek is situated near Rittem in the southeastern part of the island of Walcheren, province of Zeeland, Netherlands. The dike near Rittem was bombed October the 7th, 1944 by the allied airforces to drive the German occupation out by inundation. The dike between Rammekens, Nieuwland and Middelburg remained intact. The bombed dike was closed January the 24th 1946 and next April the part of the island where the nature reserve is situated nowadays fell dry. Land and freshwater mollusks had succumbed. In 1948 the State Forest Service started planting trees, which has resulted in ca 60 ha of deciduous wood land along the deep creeks. These creeks, formed by the tidal currents during the inundation period are no longer connected with the open sea. They contain brackish water. Salt water wells keep the salinity at 14,37-14,38‰ (samples of July 27th and 28th 1959). The living molluscs observed here are Cardium edule forma paludosa, Abra tenuis, Mya arenaria and Hydrobia stagnorum. These species did not suffer from the inundation, on the contrary, their appearance was made possible by the salt water. The land- and freshwater molluscs known from Southeastern Walcheren before the inundation are enumerated and compared with the present fauna. The freshwater species have completely disappeared and did not yet return. Three species of land molluscs recently collected in the nature reserve were known to have lived in southeastern Walcheren before the inundation. When we accept those as having belonged to the pre-war fauna, this fauna consisted of 25 species of which 19 species can be listed as members of the present fauna. The fortress of Rammekens, however, was not flooded and its fauna did not suffer from the salt water. A detailed account of the mollusc fauna of the fortress, which was built in 1547, is given. The five species recently discovered there for the first time are accepted as having lived there before the inundation. When we exclude the fauna of the fortress we find 24 species for this region before the inundation, of which 14 species at present occurring in the nature reserve have immigrated into the reserve during a period of 15 years. We do not know from where they came. The mollusc fauna of the dikes is too imperfectly known to allow of conclusions. The fortress is a possible starting point. However, there are four species living in the nature reserve now, which are not known to occur at the fortress. These at least must have come from elsewhere.