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

Özet

Feeding of non-indigenous cyclopoid copepod Oithona davisae in natural coastal phytoplankton assemblages from theSevastopol Bay, the Black Sea, in late July and in late November 2013 and in artificial phytoplankton assemblage (mixture of5 cultured microalgae) have been studied in laboratory experiments using flow cytometry. Three distinct main clusters ofphytoplankton (2 μm < ESD < 20 μm) were identified in the natural water samples in both sampling period: photosyntheticpicoeukaryotes, nanophytoplankton and nanoplanktonic cryptomonads (NanoPE). Female O. davisae grazed on all 3phytoplankton groups but the highest ingestion rate in terms of carbon was on NanoPE with the value of 0.29±0.03 μg Cpreycop-1 d-1 in July. Low abundance of 3 phytoplankton groups in late November resulted in a very low but significant carboningestion on cryptophytes (0.008±0.002 μg Cprey cop-1 d-1) than on the other groups. Clearance rates and electivity indicesconfirmed positive selection only for cryptophytes from natural phytoplankton assemblages, and for cryptophyte strain IBSSCr54 and Tetraselmis suecica from artificial plurialgal mixture. Highest daily specific carbon-rations of O. davisae femaleswere found on cryptophytes (ESD 7 - 12 μm): up to 135% and 184% body carbon d-1 in late July and on artificial phytoplanktonassemblage, respectively.