Distribution and biology of Mnemiopsis leidyi in the Northern Aegean Sea, and comparison with the indigenous Bolinopsis vitrea

Abstract

The distribution of the ctenophore Mnemiopsis leidyi in the Aegean Sea, influenced by the outflow of Black Sea water through the Dardanelles strait, has been studied since 1990. Swarms were found in the northern Aegean Sea, mainly near coastal areas, but at a lower abundance (max 150 ind. m−2) than in the Black Sea. It has been hypothesized that M. leidyi was introduced to the Aegean Sea by Black Sea water, but its presence in Saronikos Gulf and Elefsis Bay, located in the central Aegean Sea, could equally well be attributed to introduction with ballast water. No impact of M. leidyi on the mesozooplankton communities was detected in the northern Aegean Sea, probably due to its low abundance. During July 2001 the distribution and biology of M. leidyi and of the indigenous Bolinopsis vitrea were studied in the northeastern Aegean Sea. The abundance of both species was extremely low. The M. leidyi of the Aegean Sea were smaller and probably had lower fecundity than those of the Black Sea, but they presented higher metabolic and clearance rates. The metabolic and clearance rates of Bolinopsis vitrea were lower than those of M. leidyi of the same length. These results suggest a regulation of the ctenophore populations in the oligotrophic waters of the Aegean Sea.