Detection of feeding dietary Rhizostoma pulmo (Macri, 1778) in Samsun coasts of the Black Sea, Turkey

Abstract

In this study, gastric contents of the medusa Rhizostoma pulmo distributed along the Samsun coast of the Black Sea were investigated between August 2008 and January 2010. Moreover, the relationship between the umbrella diameter and prey selectivity was determined. Captured R. pulmo individuals during the sampling period varied from 14.5 to 42.5 cm in umbrella diameter. The largest umbrella diameter was observed in October in both periods of the present study. Gastric contents of total 231 R. pulmo individuals have been gathered during the sampling period from all stations. 31 taxa, 10 larvae, 2 nauplii and fish and Copepod eggs from 11 phyla have been identified in the gastric contents of R. pulmo individuals. It has been detected that, feeding choices of R. pulmo individuals have differentiated and their food count has increased due to increasing umbrella diameter (according to Spearman rank correlation, r=0.70; p<0.05). According to the gastric content analyses, the feeding dietary of this species predominantly consists of copepods and dinoflagellates. It has been observed that taxa belonging to Crustaceans (59 %; Copepods 45.9 %) and Dinoflagellates (15.4 %) were densely present in the gastric contents gathered from R. pulmo individuals. The Phylum Ciliophora was another abundantly observed group in the gastric content of R. pulmo, with a 7.2 % representation rate. It was determined that jellyfish have a wide range of nutrition from phytoplankton to fish eggs. The sort of prey and amount of nutrition in stomach contents increased in parallel with the umbrella size. It is concluded that R. pulmo has important effects on the pelagic zone of the Black Sea ecosystem.