An investigation on abundance and distribution of Mnemiopsis leidyi in Guilan waters, southwest Caspian Sea

Abstract

The alien ctenophore Mnemiopsis leidyi which was transported from the Black Sea into the Caspian Sea by the end 1990s has since affected this new ecosystem. We studied the spatial and temporal distribution of the ctenophore from July 2001 to July 2002 in three transects located in Lisar, Bandar Anzali and Sefidroud, in Guilan province. Four stations were established in each transect at a 5, 10, 20 and 50 meter bottom depth contours. Maximum observed biomass of the organism was 221.3±91g1m2 in October 2001 and the minimum was 8.3±3.8g/m2 in December 2001. The highest biomass of the organism was detected in the upper 0-20m water layer in areas 50 meters deep achieving 145.36± 67.330112. The lowest biomass was in the 20 — 50 layers in areas 50 meters deep amounting to 1.9±0.95g1m2. Small specimens less than 10 mm comprised about 97% of the sampled population and the maximum length measured at 51-55mm. The largest average biomass was 112.3±48g/m2 detected in Lisar and the smallest biomass in the range 67.17±46.8g1m2 was seen in Anzali region. It was concluded that temperature, depth, salinity and food availability affected the distribution of Mnemiopsis leidyi in the sampled areas. It is also expected that the high biomass of the organism detected in the region may have significant effects on pelagic ecosystems of the Caspian Sea.