Ecologie et reproduction de l'huitre portugaise (Crassostrea Angulata LAMARCK) dans le bassin d'Arcachon et sur la rive gauche de la Gironde

Our work on the ecology and the reproduction of C. angulata (Lamarck) in Arcachon Bay and in Gironde River confirmed and detailed a certain number of already known facts, establishes some new facts, and formulates hypotheses—and occasionally draws conclusions—on the influence of the environment on oyster development as well as on larval, fixation and the early adult phases. The first part of this study aimed to evaluate the environment in Arcachon Bay and in the Gironde River estuary. In Arcachon Bay, variation of hydrological factors depends on both the ocean and the coastal hinterland. The morphology of the sea floor and substrate characteristics were shaped by local geology and by the shallowness of the bay. Passing from south-west to east, the substrate shifts from coarse sediment, composed of sand and shell fragments and rich in carbonate, to fine sediment, richer in organic matter. Several biotopes were found in the vertical distribution of the shore. Oysters, in natural populations or in oyster farms, were found in the middle to lower intertidal zones (1.10 m). Only the lower part of oyster beds is not exposed by the tides. Oyster farms showed substrates slightly different from the non-cultivated beaches. The movement of water masses from up- to downshore is greatly reduced during neap tides. Water mass in the eastern part of the bay is only partially renewed: the initial flood phase brings back part of the water that flowed out during ebb tide before it reaches the ocean. Winds can deviate surface currents from one bank to the other in the channel. The average water temperature follows a trend roughly parallel to that of air. Water temperature is generally greater by a factor of 1.07. In February, differences in water and air temperature are the greatest and in July, the lowest. There is a seasonal pattern of temperature variation of the bay's waters during a tide, with a winter period with two maxima at high tide; two transitory periods, in spring and in autumn, when temperatures are more stable, rising or falling by increments with maxima during low tide or during the first hours of afternoon flood tides; and a summer period with two maxima corresponding to low tide or the first hours of flood tide. ...(unverified OCR)