Abundance and distribution of the Caspian Sea Ctenophore (Mnemiopsis leidyi)

The alien ctenophore Mnemiopsis leidyi was entered from the Black Sea into the Caspian Sea by late 1990s. It has been reported that the M. leidyi caused the dramatic decrease of zooplonkton and pelagic fish stock in the Caspian Sea. In this study، spatial and temporal distribution of M. leidyi was studied during year 2004 in four transects Bandar Anzali، Khazarabad، Turkman and Miankaleh in the south coasts of the Caspian Sea. Results showed that M. leidyi achieved maximum abundance and biomass (6061±5830 n. m2 and 745±715. 9 g. m2) in the upper layer of 50 (0-20) m depth during autumn. The Minimum biomass and abundance (22. 78±9. 64 g. m2 and 385±226 n. m2) of the ctenophore were measured in the coasts regions (5 and 10 m depth) during spring. The biomass and abundance of M. leidyi were more in southeastern of Caspian Sea than the southwestern. Larvae (<5 mm) contributed about 85% total abundance of the population. The maximum size of the measured M. leidyi was 64 mm in length. The effects of abiotic factors on distribution of M. leidyi was discussed.