Laboratory experiments were performed to determine the growth and grazing capabilities of Oblea rotunda, a pallium-feeding dinoflagellate. Although Oblea can feed and grow on a wide range of phytoplankton species, the highest observed growth rates (approximately 1 doubling d-1) were supported by the large diatom Ditylum brightwellii. Functional and numerical response curves, obtained with the green alga Dunaliella tertiolecta and D. brightwellii as foods, were typical in form of those obtained previously for other planktonic protozoans. Ditylum, however, consistently supported higher rates of growth and grazing than Dunaliella. Gross growth efficiencies for Oblea were relatively high. A chemosensory response to phytoplankton exudates was observed during motion analysis of swimming behavior; no response to mechanical cues was evident. Long-term behavioral responses to different phytoplankton species or concentrations were not observed. The wide range of food species available to Oblea suggests that size- or taxon-based parameterizations of such grazers in food-web models may be inadequate to describe actual grazing interactions.
