Growth and grazing of a naked heterotrophic dinoflagellate, Gyrodinium dominans

Abstract

Growth and grazing rates of a naked heterotrophic dinoflagellate, Gyrodinium dominans [equivalent spherical diameter (ESD) = ca 20 μm], were examined in batch cultures. Strains isolated from the Seto Inland Sea (Harima strain) and Tokyo Bay (Tokyo strain) in Japan were used for the experiments. Both strains grew well when fed amorphous materials (such as bacterial flocs with attached nanoflagellates and aggregates of a small diatom) and plankton species with ESD of 15 to 26 μm. The Tokyo strain also grew rapidly when fed small (ca 5 μm) phytoplankton species at levels higher than 1 x 10 5 ml -1 . However, rates of ingestion of Nephroselmis aff. rotunda (ESD = 4.5 μm) by the Tokyo strain were too low to sustain rapid growth of G. dominans at natural levels of small (2 to 8 μm) flagellate abundance ( 15 μm) nanoflagellates such as Gymnodinium mikimotoi.