Distribution and size structure of comb jellyfish, Mnemiopsis leidyi (Ctenophora) in the southwestern Caspian Sea

Abstract

Temporal and vertical distributions of Mnemiopsis leidyi were studied along three transects namely Lisar, Anzali and Sephidrood in the southwestern Caspian Sea during 2001 to 2010. The maximum lengths of the ctenophore were 60 to 70 mm, and bulk of individuals (90.6%) were <5 mm in length. The means of abundance and biomass during the whole period were 3032 ind/m2 and 293.54 g/m2, respectively. The highest average abundance value (1017 ind/m2) was measured in summer 2006 and the lowest abundance value (54 ind/m2) was in spring 2010. The average biomass of M. leidyi ranged between 1175.40 and 0.85 g/m2 in summer 2005 and winter 2008, respectively. The highest annual of abundance and biomass were obtained in 2005 and 2006. The dominant of M. leidyi bulk occurred above 20 m depth, whilst the ctenophore population sharply decreased below 20 m. The seasonal pattern of M. leidyi is related to water temperature, as evidenced from the positive correlation between the water temperature and M. leidyi population. Key words: Mnemiopsis leidyi, abundance, biomass, size, Caspian Sea.