THE SEASONAL OCCURRENCE AND ABUNDANCE OF GELATINOUS MACROZOOPLANKTON IN IZMIT BAY (THE NORTHEASTERN MARMARA SEA)

The seasonal occurrence and abundance of gelatinous macrozooplankton in Izmit Bay (the northeastern Marmara Sea)

Melek Isinibilir

Faculty of Fisheries, Istanbul University, 34130, Laleli-Istanbul, TURKEY

Abstract

In this study, temporal distributions of four gelatinous zooplankton, the scyphozoan Aurelia aurita and the ctenophores Mnemiopsis leidyiBeroe ovata and Pleurobrachia pileus, were evaluated using data obtained from 17 cruises to Izmit Bay carried out from July 2001 to November 2002. Mnemiopsis leidyi was always present in all seasons. The appearance of Beroe ovata resulted in a sharp decrease of M. leidyi biomass. Beroe ovata was found only in summer-autumn periods in Izmit Bay, with the highest average abundance (120.9 ± 250.5 ind. m-3) occurring in September 2001. Pleurobrachia pileus was observed from February to June 2002. Aurelia aurita was always present in the all seasons Small individuals of M. leidyi (<10 mm) were observed throughout the year, and mean lengths of individuals increased from summer to spring, when large individuals dominated the population.

Keywords: Gelatinous macrozooplankton, abundance, size distribution, Izmit Bay