Identification and density determination of jelly zooplanktons in Khuzestan coastal waters

Recently, we have been encountered to increasing jellyfish biomass in the world tropical coastal waters and due to their role in ecosystem food web, can be made direct and indirect effects on marine stocks and causing problems for fisherman’s communities. Now, the number of studies on this animal groups and factors which caused to jellyfish bloom has been increased. Present study was carried out for identification and density estimation of jellyfishes in the East and West coasts of Khure-Musa canal in Khuzestan coastal waters in North-West of Persian Gulf. Monthly samples were collected by two sampling methods from randomly sites in studied area in day light during February 2007 to January 2008. Small jellyfishes were collected by using 500 micron mesh net and density was calculated as number per 10 square meters. Large jellies were collected by using shrimp trawl net and quantity measurements were done by swept area methods. Totally, 18 species including 9 hydromedusae, 2 Scyphomedusae, 3 Siphonophorae and two Ctenophores were identified. Generally from 5357 separated small jellyfish, 56.6 % was from East and 43.4 % was from west coasts. Ctenophore, Pleurobranchia (31%) and then the Hydromedusa Eiren hexanemalis (22%) were the most abundant taxa. The maximum number of jellyfish (1080 per 10m2) was observed in western coasts in July and then decrease in summer and autumn. In contrast to Eastern coasts, the highest frequency (655 per 10 m2) was observed in western coasts in September. Two peaks of frequency in May-June and in summer to fall were observed in this area. The highest frequency of macro jellyfishes were in July and mostly in East coasts (2811 per km2). During February 2007 to February 2008 Catostylos tagi and Chrysoara hysocello were dominated. Monthly jellyfish abundance variation showed inverse relation between Eastern and Western coasts. The maximum diversity was in August in Eastern coast and July in Western coasts. The minimum values were calculated in winter months in two areas. Obviously, with increasing jellyfish abundance, in summer months, fish larvae population decreased. Jellyfish explosion can be caused by several factors, fishing pressure and removing top predators from food web, climate change, global warming and eutrophication phenomena are defined as the major factors in jellyfish bloom in worldwide tropical coastal waters. Therefore human activities enhance the occurrence of this phenomenon. Recent drought, decreasing freshwater input, increasing waste discharge and overfishing are probable causes for jelly blooms in Khuzestan coastal waters.

Iranian Fisheries Science Research Institute

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