DISTRIBUTION AND ABUNDANCE OF PLEUROBRACHIA-RHODOPIS (CYDIPPID CTENOPHORE) IN THE BAY OF VILLEFRANCHE-SUR-MER (NORTHWESTERN MEDITERRANEAN) STUDIED USING 3 DIFFERENT PLANKTONIC TIME-SERIES

The ctenophore Pleurobrachia rhodopis (Chun, 1880) was studied in thre e different time series of samples made in the bay of Villefranche-sur -Mer (northwestern Mediterranean). A daily series (from 1993 to 1995) was characterised by large abundance differences during the 3 years. A weekly series (from 1993 to 1995) showed that Pleurobrachia was not l imited to a specified depth and that their vertical distribution varie d with environmental parameters. From 1966 to 1993, there were some ye ars of high abundance, during which many Pleurobrachia were observed, and some years with low abundances. When this species was present, abu ndance maxima occurred always during the spring. Comparisons of fluctu ations of the population with those in hydrological parameters showed that this ctenophore occurred when temperatures were between 14 and 19 degrees C. This species reacted also to salinity variations.