Inter-Research
Aquatic Microbial Ecology

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 10⁵ 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 (<3 x 10⁴ ml^-1). Ingestion of Heterocapsa triquetra (ESD = 15.3 µm) followed Michaelis-Menten kinetics with half-saturation constants of 820 and 180 ml^-1 and maximum ingestion rates of 0.82 and 0.59 prey predator^-1 h^-1 for the Harima and Tokyo strains, respectively. The clearance rates of both strains feeding on H. triquetra were about 2 orders of magnitude higher than those for N. aff. rotunda. These results indicate that G. dominans can play an important role in the decline of red tides caused by large (> 15 µm) nanoflagellates such as Gymnodinium mikimotoi.

KEY WORDS: Grazing . Growth . Heterotrophic dinoflagellate . Microzooplankton . Red tide

Published in AME Vol. 9, No. 2 (1995) on August 31
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 1995