The invader into the Caspian Sea ctenophore Mnemiopsis and its initial effect on the pelagic ecosystem

The distribution and biology of the new invader into the Caspian Sea-the ca rnivorous ctenophore Mnemiopsis-were studied. Data on the mnemiopsis disper sion in the North, Middle, and South Caspian Sea; it's abundance; biomass; and seasonal dynamics in 2000 are presented for the first time. In July, mn emiopsis was widely spread in the Middle Caspian and the northern part of t he South Caspian Sea, while no ctenophore was found in the North Caspian Se a. In the North Caspian it was first found in September. In October, in the North Caspian Sea, the mnemiopsis habitat expanded, the biomass increased 3.5 times, and, at some places, its abundance reached 170 ind./m(2). The no rthward penetration was limited by the 4 parts per thousand isohaline. Prel iminary data on the dependence of the wet weight on body length, metabolic activity, and dry substance content were obtained. A comparative analysis o f the species composition, abundance, and biomass of the North Caspian zoop lankton in July and October is presented. A decrease in the zooplankton abu ndance (5.3 times) and biomass (6 times) was recorded in October in compari son to July; the decrease of the Copepoda abundance was the most considerab le.