The solar eclipse and the migration of some planktonic crustacea in Lake Geneva.

Four campaigns were performed during the partial eclipse of sun (August 11, 1999) in order to improve the influence of light on the spatial segregatio n and the vertical migration of zooplankton. The fall of light intensity ha s engender a vertical migration of Cyclops prealpinus and Daphnia hyalina w hich bait an upward movement at the beginning of the eclipse which continue s as far as the maximum of this last, then they sink front the end of this phenomenon. Eudiaptomus gracilis, mainly localised in the layer 20-30 m, in creased its abundance in the layer 10-20 m at the maximum of the eclipse. E . gracilis begins a short surfacing slower than C. prealpinus and D. hyalin a. Influence of light on these migrations would be more important in case o f a total eclipse because this phenomenon induces same light conditions tha n during a nycthemeral cycle.