TIME AND SPATIAL DYNAMICS OF MEDITERRANEAN LAGOON MACROBENTHOS DURING AN EXCEPTIONALLY PROLONGED INTERRUPTION OF FRESH-WATER INPUTS

Heavy and constant inputs of freshwater into the north of the Berre lagoon over a period of more than 20 years, due to the diversion of the Durance River, resulted in the total disappearance of the macrobenthos at depths of more than 5 m. Only one community that had adapted well to the brackish conditions had survived on the thin coastal fringe. In 1990, abnormal drought conditions resulted in the interruption of freshwater inputs for a period of 7 months. A study of the changes in the benthic fauna subjected to these new ecological conditions, carried out during the second semester of 1990, shows that the prolonged stoppage of freshwater inputs was marked mainly by the appearance of marine species on the coastal fringe within the brackish community and by the colonization of the azoic bottoms by various macrobenthic species. This recruitment can be attributed to the stable conditions prevailing in the lagoon during this period, with no sharp fluctuations in salinity, no silt discharge and in particular an increase in the dissolved oxygen content in the water column. The colonization that was observed demonstrates that the chemical nature of the Berre lagoon sediments does not constitute a major limiting factor compared to the freshwater inputs.