Peuplements benthiques à Cyanophycées des marais salants de Salin-de-Giraud (Sud de la France)

Abstract

In Salin-de-Giraud solar salt work pools, Cyanophyceae are dominant in benthic populations. Two main types of communities can be recognized : 1) Laminated mats in weak salinity areas (<150 g/1) with Microcoleus chthonoplastes frequently exclusive (but which may be covered by a Lyngbya aestuarii layer), being the result of superposition in time of two competitive phenomena : Cyanophycean growth and sedimentary contribution either of detrital or chemical origin. As the gypsum precipitation occurs, Microcoleus mats disappear. 2) Communities associated with gypsum and halite crusts. In gypsum pools, they may be composed of several layers : a) a lower purple layer of ph.otosynthetic bacteria ; b) a mid dark-green layer of filamentous Cyanophyceae (Phormidium and Spirulina species) mixed with some coccoids (Aphanothece div. sp. essentially) ; c) an upper orange-colored layer of coccoids (with an Aphanothece sp. as major component) may grow during summer, but disappears during winter when pools are emptied, which is the rule in Salin-de-Giraud. The basal level of halite crust is colonized by a filamentous form Phormidium sp. For these communities, stratification of species is associated to physiological properties of organisms, and sedimentary deposits only act as a support in such pools.