LAUSR

ABSTRACT The zooplankton species Oithona davisae is indigenous to coastal areas of Japan and the China Seas. It has, however, successfully invaded many other coastal marine regions such as San Francisco Bay, the Mediterranean Sea, the North Sea and the Black Sea. It is transported most probably in ballast water tanks. This is the first report of O. davisae in the coastal regions of the southern Black Sea (Anatolian coast). Based on monthly plankton sampling at two stations (Sürmene Bay), the seasonal dynamics of O. davisae were investigated. The highest abundance occurred at the coastal station (49,761 ind. m−3) in December and in October at the offshore station (8896 ind. m−3). The egg-carrying copepod O. davisae is more abundant in September (4571 ind. m−3) at the coastal station and in August (952 ind. m−3) at the offshore station. Expansion of this invasive copepod along the Black Sea coasts is reported by another country also. According to our results this invasive species may replace its native congener, Oithona nana. It can be hypothesized that O. davisae is one of the key species for energy transfer to the upper level of the food web from the microbial loop, which has recently become important in the Black Sea.