Distribution and abundance of ctenophores and their zooplankton food in the Black Sea. II. Mnemiopsis leidyi

The distribution of Mnemiopsis leidyi Agassiz, 1865 in the Black Sea was de termined using plankton samples collected above the anoxic zone (maximum de pth 200 m) in the summer, winter, and spring from 1991 to 1995. Distributio n was patchy. Average biomasses of 15 to 500 g m(-2) were measured, and abu ndances varied from 10 to 180 ind m(-2). Biomass and abundance peaked in wi nter, and there was a secondary peak in the summer. The distribution of M. leidyi was correlated with hydrographic features in the Black Sea with high er concentrations in anticyclonic gyres. The centers of the two main cyclon ic gyres generally had a low biomass of M. leidyi. From July 1992 to March 1995, the populations were largely offshore. M. leidyi were confined to the upper part of the mixed layer both day and night, Some individuals display ed a negative taxis to daylight and were concentrated below the thermocline at night. Smaller M. leidyi (1.5 to 2 cm) were present in the winter, and individuals reached maximum size in the summer. Although reproduction was c ontinuous throughout the year, there were two distinct peaks: the larger pe ak in the summer and the smaller peak in the winter. Microscopic analysis o f stomach contents showed that copepods and molluscs form their main diet.