Zooplankton community state in the Northeastern Marmara Sea during early autumn with comments on mass mortality of the Black Sea species due to the salinity gradient

Abstract

In October 2005 species composition and abundance of mesozooplankton collected in the Black Sea (near the entrance of the Bosphorus) and in the Marmara Sea (near the exit of the Bosphorus and Prince Islands) were studied taking into account the number of live and dead individuals. Along the Bosphorus, the numbers of the Black Sea originated Copepoda species reduced whilst the abundance of Cladocera and Oikopleura dioica increased towards the Marmara. The Black Sea species constituting 78% of total fodder zooplankton abundance in the Marmara Sea aggregated mainly in the subsurface layers with lower salinity. In the layers deeper than salinity gradient (25-50 m) 57% of the individuals from these taxa were dead being at different stages of decomposition. Respiration rates of copepods also differed among layers of distinct salinity.