Interannual changes in the biomass of the Black Sea Gelatinous zooplankton

The 15 year changes in the total gelatinous biomass consist of a general trend to increase, from 250 g m^-2 in 1980 to 2500 g m^-2 in 1995, and fluctuations with a period of ~4 years performed against the background of this trend in the upper 150 m layer. Different species occupying distinct trophic niches form these peaks. When represented as the percentage of the total zooplankton biomass, Aurelia aurita and Mnemiopsis leidyi exhibit the contra-phase fluctuations where a sharp increase in M. leidyi is accompanied by a decrease in the A. aurita biomass.