FLORA AND FAUNA OF THE SUBLITTORAL HARD SUBSTRATA IN THE OOSTERSCHELDE (THE NETHERLANDS) - INTERACTIONS WITH THE NORTH-SEA AND THE INFLUENCE OF A STORM-SURGE BARRIER

Since 1979 the flora and fauna of the artificial rocky shores of the Oosterschelde estuary have been investigated by diving biologists. Spatial and temporal patterns of species diversity and biomass were studied and several groups of species ('communities') were distinguished. A west-east gradient in species composition was found. Species distribution proved to be mainly determined by current velocities, silt and plankton concentrations in the water, underwater irradiance, and the nature of the substratum. Some indications of migration between the basin and the North Sea are shown. Biomass of the hard substratum fauna was compared with that of the soft bottom fauna; the ratio appeared to be about 1 : 2, which is surprisingly high considering the small area available for hard substratum fauna. The key to the interactions with the North Sea is found in the water movements and the volume of water passing through the mouth of the basin during each tide. The abiotic and subsequent biotic changes in the basin caused by the building of the storm surge barrier are discussed, and used to illustrate the measure of dependence of the Oosterschelde on the North Sea. © 1990 Kluwer Academic Publishers.