Grazing and Feeding Selectivity of Oithona davisae in the Black Sea: Importance of Cryptophytes

Feeding of non-indigenous cyclopoid copepod Oithona davisae in natural coastal phytoplankton assemblages from the Sevastopol Bay, the Black Sea, in late July and in late November 2013 and in artificial phytoplankton assemblage (mixture of 5 cultured microalgae) have been studied in laboratory experiments using flow cytometry. Three distinct main clusters of phytoplankton (2 mu m < ESD < 20 mu m) were identified in the natural water samples in both sampling period: photosynthetic picoeukaryotes, nanophytoplankton and nanoplanktonic cryptomonads (NanoPE). Female O. davisae grazed on all 3 phytoplankton groups but the highest ingestion rate in terms of carbon was on NanoPE with the value of 0.29 +/- 0.03 mu g Cprey cop-1 d-1 in July. Low abundance of 3 phytoplankton groups in late November resulted in a very low but significant carbon ingestion on cryptophytes (0.008 +/- 0.002 mu g Cprey cop-1 d-1) than on the other groups. Clearance rates and electivity indices confirmed positive selection only for cryptophytes from natural phytoplankton assemblages, and for cryptophyte strain IBSS-Cr54 and Tetraselmis suecica from artificial plurialgal mixture. Highest daily specific carbon-rations of O. davisae females were found on cryptophytes (ESD 7 - 12 mu m): up to 135% and 184% body carbon d-1 in late July and on artificial phytoplankton assemblage, respectively.