Effet d'une crise dystrophique dans l'etang de Salses-Leucate

The dystrophic crisis in the lagoon of Salses-Leucae in 1979-1980 resulted in a bloom of the chlorophyceae Nannochloris sp. which attained a density in the order of 10 super(9) cells/litre. The worst effect was the destruction of oyster and mussel cultures because of overfeeding. This bloom also caused high turbidity which induced the destruction of large parts of sea-grass communities (Zostera)). One year after the beginning of this crisis, a gradual improvement of ecological conditions was noted, especially in the pelagic zone. The benthic environment recovered at a much slower rate. Sea-grass showed signs of recovery, organic matter concentrations and bacterial populations decreased. Furthermore, the macrofauna density increased notably. Nevertheless, the situation remained precarious, for in October, concentrations of organic matter and sulfate-reducing bacteria were still high in sediments. The considerable phytoplanktonic development exists because of large amounts of mineral elements, probably untreated sewage.