Species Composition, Distribution and Abundance of Hydromedusae in the Exclusive Economic Zone of the East Coast of India

Abstract

Based on zooplankton collections made by Fisheries Ocean Research Vessel Sagar Sampada Central Marine Fisheries Research Institute, India, during the period 1986-1990, 356 samples from 18 cruises from Sri Lanka to Calcutta coast were analysed. The hydromedusae were encountered in 273 samples and more than 62 species were found. Liriope tetraphylla dominated in the percentage of occurrence and population density. Aglaura hemistoma, Solmundella bitentaculata, Rhopalonema velatum, Cytaeis tetrastyla, Bougainvillia fulva and Phialidium hemisphaericum were the commonly occurring species. The maximum species diversity was noticed away from the nearshore stations, while maximum population density was from nearshore stations. reported by Navas (1971), Vannucci and Navas (1973a, b, c) and Santhakumari (1977a) based on the samples in the International Indian Ocean Expedition (1962-1965). But in this expedition coastal areas were not thoroughly sampled. A comprehensive study from the coast of India, especially in its exclusive economic zone (EEZ), has not been undertaken. The available information on the distribution of hydromedusae is confined to areas off the southwest coast of India (Nair, 1954; Vannucci and Santhakumari, 1969; Santhakumari, 1977a, b, 1991). The only a report about the destribution of hydromedusae from the east coast of India is by Ganapati and Nagabhushanam (1958) who recorded the seasonal distribution of hydromedusae from Visakhapatnam. The present paper deals with the distribution of hydromedusae based on the material collected by FOR V Sagar Sampada from the EEZ of the east coast of India. Materials and Methods Samples were collected in 18 cruises on board FORV Sagar Sampada from the EEZ of the east coast of India, from Sri Lanka to Calcutta, during the period 1986-1990. By an oblique haul from 150m depth to surface using Bongo net (mouth diameter 60 em; mesh aperture 0.33 mm) equipped with a calibrated flow meter, 356 zooplankton samples were taken and preserved in 5% formalin sea water solution, and the hydromedusae were separated and analysed. The sampling details were presented in the cruise reports (Central Marine Fisheries Research Institute, 1986). Hydromedusae counts were transformed to numbers per unit volume using flow meter data.