Phytobenthos et productivité primaire d'un lac de haute montagne dans les Pyrénées centrales

Abstract

The importance of the benthic algal community in the primary productivity of a high moutain lake is evaluated. The lithophytic algae of the littoral zone (6 - 19 m), form a biomass about 140 times greater than the mean biomass of the phytoplankton during the summer. Nitella flexilis forms 80 % of the benthic algal biomass; the variations in its chlorophyll content show an adaptation to the light climate which it partly determines. The colonisation of artificial substrata was found to be not very adequate for evaluating the production of periphyton; it indicated a productivity 10 times less in the littoral zone than in the littoral-profundal zone. Measurements, with 14C, of the rate of assimilation of Nitella flexilis and epiphytic algae revealed that, as a consequence of the phenomena of compensation by the development of periphyton and the adjustment of chlorophyll content, photosynthetic activity is not very dependent on light. The contribution of benthic algae to the primary production is estimated to be 30 %. Their role in the cycling of chemical elements is considered. © 1973 Masson.