Gyrodinium undulans Hulburt, a marine dinoflagellate feeding on the bloom-forming diatom Odontella aurita, and on copeod and rotifer eggs

Abstract

The marine dinoflagellate Gyrodinium undulans was discovered as a feeder on the planktonic diatom Odontella aurita. Each year, during winter and early spring, a certain percentage of cells of this bloom-forming diatom, in the Wadden Sea along the North Sea coast, was regularly found affected by the flagellate. Supplied with the food diatom O. aurita was dinoflagellate could be maintained successfully in clonal culture. The vegatative life cycle was studied, mainly by light microscopy on live material, with special regard to the mode of food uptake. Food is taken up by a so-called phagopod, emerging from the antapex of the flagellate. Only fluid or tiny prey material could be transported through the phagopod. Larger organelles like the chloroplasts of Odontella are not ingested and are left behind in the diatom cell. Thereafter, the detached dinoflagellate reproduces by cell division, occasionally followed by a second division. As yet, stages of secual reproduction and possible formation of resting cysts could not be recognized, neither from wild material nor from laboratory cultures. Palmelloid stages (sometimes with a delicate wall) occurring in ageing cultures may at least partly function as temporary resting stages. The winter species G. undulans strongly resembles Syltodinium listii, a summer species feeding on copepod and rotifer eggs. Surprisingly, in a few cases this prey material was accepted by G. undulans as well, at least under culture conditions. When fed with copepod eggs, the dinoflagellate devleloped into a large trophont, giving rise thereafter by repeated binary fission to 4, 8 or 16 flagellates, as a result of a single feeding act. A re-examination of both species under simultaneous culture conditions is planned.