WASTE-WATER DISCHARGE, SEAGRASS DECLINE AND ALGAL PROLIFERATION ON THE COTE-DAZUR

The green alga, Caulerpa taxifolia, has recently proliferated in areas of the N-W Mediterranean that were previously dominated by the seagra ss Posidonia oceanica. Sediments in areas of proliferation had high ex oenzyme activities, NH4+ concentrations and production rates, but very low capacities to transform organic-N into NH4+ relative to the quant ity of organic material available, All sediments supporting C. taxifol ia contained large quantities of precipitated phosphorus and exhibited extremely low capacities to transform NH4+ into NO2 and NO3-. Low tra nsformative capacities and high phosphate concentrations are character istic of sediments that have been polluted by urban wastewater, Where C. taxifolia did not exist, or where growth had stabilized, sediments had exoenzyme activities, NH4+ concentrations and NH4+ production rate s that were proportional to organic-N transformative potential. AII se diments contained significant concentrations of non-crystalline sulphi de, Caulerpa taxifolia proliferation may be linked to enrichment of su bstrata by urban wastewater and dead or dying seagrass vegetation. (C) 1997 Elsevier Science Ltd.