Comparative size-specific grazing rates in field populations of ciliates and dinoflagellates

Specific feeding rates of ciliates and thecate and gymnodinoid dinoflagellates on the natural food spectrum were compared, applying a dual-label isotope method in coastal waters off Oregon, USA. Ciliates had the highest size-specific clearance rates on heterotrophic food sources with an average of 3.9×10⁵ body volumes (BV)h^-1. Gymnodinoid dinoflagellates strongly selected for photographic food sources and showed the highest size-specific clearance rates on phototrophs with an average of 2.2×10⁵ BV h^-1). The range of clearance rates on photosynthetic organisms in gymnodinoids overlapped with that in the ciliates. Data indicate that in gymnodinoid dinoflagellates, small cells have higher size-specific clearance rates than larger cells. -from Authors