THE MEDUSAE (CNIDARIA, HYDROZOA) AND THEIR TROPHIC ENVIRONMENT - AN EXAMPLE IN THE NORTH-WESTERN MEDITERRANEAN

Literature on Medusae in the Mediterranean is briefly reviewed. paying particular attention to differences among their life histories, metho ds of feeding, quantitative trophic parameters and patterns of occurre nce. The responses of different species to spatio-temporal variations in prey abundance are analysed. Holoplanktonic medusae largely dominat e the Mediterranean, while meroplanktonic medusae dominate most other seas. This probably reflects the lower food intake rates of holoplankt onic forms associated with their longer lifetimes in the plankton, wit h consequent adaptation to the largely oligotrophic environment of the Mediterranean. When and where the Mediterranean shows high prey abund ance, meroplanktonic medusae dominate. Feeding activity is linked to h ydrological and meteorological variables in medusae such as Pelagia no ctiluca, suggesting that feeding in medusae needs to be better quantif ied to allow further understanding of how changes in weather and water movement affect medusan production and abundance.