Etude des eaux rouges dues � la prolif�ration des bact�ries photosynth�tiques sulfo-oxydantes dans l'�tang du Pr�vost, lagune saum�tre m�diterran�enne

Abstract

Dystrophic crises or “malaigues” with red water, were observed in summer, in Mediterranean brackish lagoons near Montpellier, France. During July 1976, the photosynthetic sulfide-oxidizing bacteria causing this phenomenon were isolated from the Prevost lagoon. The most important genera isolated from this red water wereChromatium, Thiocystis andThiocapsa (Chromatiaceae): the predominant species wasThiocapsa roseopersicina. Water and sediment samples from the same lagoon were collected during the winter season (October 1976 and January 1977) and were enriched with organic matter. The samples were incubated in aquaria under artificial light (800 to 1000 lux) at room temperature (ca. 22°C). Eight to 10 days later, red water developed which was similar to that observedin situ in summer. These red waters develop under conditions of anaerobiosis and H2S production. Such conditions are necessary for the growth of Chromatiaceae. Excessive deposists of organic matter in the lagoon water lead to increased oxygen consumption and overproduction of hydrogen sulfide, which can be oxidized by photosynthetic sulfideoxidizing bacteria. This bacteria “bloom” (causing the red water) removes the hydrogen sulfide, thus re-establishing aerobiotic conditions in the water of the Prevost lagoon.