Recherches écologiques sur les faunes des plages arbitées de la région d'Arcachon

Abstract

In these ecological studies of the sheltered beaches of the bay of Arcachon (France), the author distinguishes and locates four traditional zones: slikke, upper slikke, schorre and parhalian zone. Animal communities and edaphic structures of each zone are treated in detail. In the slikke, four fundamental facies are distinguished:Zostera nana zones, bare sands (such as Arenicola sands), Nereis diversicolor slime and Scrobicularia slime. Each facies is analyzed with regard to its amount of water, porosity, salinity, pH and dissolved oxygen content, as well as its hypsometric distribution. With respect to the fauna of sand and slime slikkes, the importance of the endogeous macrofauna, its infralittoral characteristics and the low degree of mobility of its species are emphasized. In the upper slikke five facies are described:Bledius spectabilis clay sands, Corophium volutator slimy sands, Bledius arenarius porous sands, Spartina maritima areas and micro cliffs. Again, abiotic characteristics and animal communities of each facies are studied successively. The importance of edaphic structures for the distribution of animal communities, and vice versa, is stressed. For instance, the amphipod Corophium volutator and the coleopteran Bledius spectabilis build tubes with firm and permanent inner surfaces only in certain types of sediment: yet, while the Bledius spectabilis tubes are dense and watertight, those of Corophium volutator are less tight and often flooded. Thus, the presence of the insect allows a supralittoral fauna to establish itself, whereas that of the amphipod is, in contrast, accompanied by a mediolittoral fauna resistant to flooding. In the schorre and parhalian zone, endogeous macrofauna elements are entirely absent; the vagrant epigeous species exhibit considerable degrees of mobility, migrating according to tidal rhythms. In summer, the schorre zone shelters both marine supralittoral or halobiotic species as well as adlittoral "haloxene" species which, coming from the parhalian zone, are attracted by the trophically rich Puccinellietum. In winter, however, frequent floodings of the schorre force the fauna to retreat to the parhalian zone for shelter. A classification is presented of the facies studied, based on the amount of water ecologically usable by their respective macrofaunas. The relationships between slikke, upper slikke, schorre and parhalian zone on the one hand, and the intertidal zones on the other are illustrated in the form of a synopsis. Finally, a comparison is made between animal communities of sheltered and of partly sheltered beaches. © 1969 Biologischen Anstalt Helgoland.