GROWTH OF CLYTIA SPP HYDROMEDUSAE (CNIDARIA, THECATA) - EFFECTS OF TEMPERATURE AND FOOD AVAILABILITY

The growth of Clytia spp. hydromedusae was observed at 15, 18, 21 and 25-degrees-C using three food concentrations, 7, 25 and 50 copepods . l-1. The medusae had an initial diameter of 2-3 mm which, in the best combination of temperature and food concentration, reached 10 mm in 30 days. Growth was dependent on temperature and food concentration. The daily diameter growth was significant only when the food concentration was over 25 prey . l-1 and temperature ranged between 15 and 21-degrees-C. With 7 copepods . l-1 medusae did not grow. At 25-degrees-C the medusae showed a high mortality rate, and negative growth. Growth occurred when the carbon specific daily ration lay between 50 and 350%. The favourable period for the growth of the Clytia spp. population in the Bay of Villefranche-sur-Mer on the basis of experimental results was from March to June which corresponded to the seasonal distribution of the in situ population.