Le phytoplancton des étangs de Berre et Vaïne (Méditerranée Nord‐occidentale)

Abstract

Phytoplankton of the Etang de Berre and Etang de Vaïne (N.W. Mediterranean)The phytoplankton in the brackish Etang de Berre and Etang de Vaïne was studied regularly at 12 stations for two years. The recent diversion of the Durance River into the Etang de Berre has effected a fundamental change in this formerly marine environment, which has had a great impact on its plankton populations. A total of 182 taxa were identified, including 111 Bacillariophyceae, 44 Chlorophyceae, and 15 Cyanophyceae. The most abundant species are small freshwater algae, mainly Chlorophyceae, since the salinity is generally less than 3 0/00. However, during summer and fall, as well as in waters near the bottom, the salinity can reach 15 0/00 and marine diatoms are predominant.Because the nutrients in the environment are constantly replenished, phytoplankters are always numerous, ranging in abundance between several million to several hundred million per liter. There is a somewhat irregular seasonal cycle. The average density is about 108 cells/1 in the Etang de Berre, and about double that amount in the Etang de Vaïne. Differences in phytoplankton abundance and composition at the various stations or at various depths are slight.