A multi-year time series of Hydromedusae sampled in discrete depth strata at a deep water station off Villefranche Bay (Mediterranean sea) from 1963 to 1966

From samples obtained over 3 years from 1963 to 1966, off Villefranche Bay from surface to the depth of 600 m, several taxonomic groups have been studied, among them the medusa presented here. From data on the 877 samples collected it is possible to identify three communities in relation to hydrographical structures : the first, after the spring bloom of phytoplankton and copepods, the second in summer above the thermocline and, the third community, a stable assemblage of species in deep waters with their occurrence in the superficial waters linked to the hydrodynamical processes during the winter mixis period. The effects of both hydrological and biological stratification, during three years at a station Point A, situated in offshore waters of Villefranche Bay, North Western Mediterranean Sea can explain the difference between meroplanktonic and holoplanktonic species appears in their occurrence in surface waters.