THE BAY OF BREST - ENVIRONMENTAL DISTURBA NCE AND ITS IMPACT ON THE BIOTA

The Bay of Brest constitute a semi-enclosed system within which inflow from the surrounding watershed combines with domestic and industrial discharges. Sedentary organisms, such as Molluscs and Urchins, by inte grating the resultant suite of impacts, are an excellent tool by which to evaluate the disturbances thus recorded by the ecosystem. Threaten ed by eutrophication, the pelagic system is resisting for the most par t, although signs that should cause concern are appearing in certain a reas, in spite of the strong tidal currents and efficient pelagic-bent hic coupling. The set of tools used reveals a contrasting situation be tween the southern and northern basins. In the latter sector, the pres ence of excess organic material, PCBs, hydrocarbons, heavy metals, pes ticides, herbicides, etc. explains the present state of general biolog ical imbalance. This is the case, however, neither in the central part of the Bay nor in the southern basin, as shown by the finding that th e biological cycle of the Scallop remains unaffected, except when cata strophic toxic plankton events occur during the larval phase.