Biological diversity and seasonal variation of mesozooplankton in the southeastern Black Sea coastal ecosystem

In this study, the seasonal distribution of mesozooplankton was investigated between 1999 and 2006 at a station located in the southeastern Black Sea region. A total of 40 cruises were done within the southeastern continental shelf throughout this period in order to collect mesozooplankton samples. A total of 10 mesozooplankton species were identified. The average annual highest abundances of species were 67,770 ind./m^2 in 2000 (Penilia avirostris), 50,048 ind./m^2 in 2001 (Sagitta setosa), 42,143 ind./m2 in 2006 (Oikopleura dioica), 27,987 ind./m^2 in 2005 (Acartia clausi), 25,792 ind./m^2 in 2001 (Oithona similis), 24,806 ind./m^2 in 2005 (Pseudocalanus elongatus), 12,094 ind./m^2 in 2005 (Paracalanus parvus), and 11,697 ind./m^2 in 2001 (Calanus euxinus). Calanus euxinus and Pseudocalanus elongatus were determined as cold-water species, having high abundance in winter and early spring. The species of Acartia clausi and Oithona similis were assessed as species observed in all seasons. According to the Bray–Curtis similarity index, the copepod species showed seasonal differences. Summer and early autumn were found to be different from other sampling periods in terms of population structure. The results of this study will form a basis for long-term mesozooplankton monitoring studies in the Black Sea coastal ecosystem.