Spatial and Temporal Aspects of Mixotrophy In Chesapeake Bay Dinoflagellates

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Abstract
Gymnodinium sanguineum, Gyrodinium uncatenum, and Ceratium furca are large phototrophic dinoflagellates that commonly form red tides in the mesohaline portion of Chesapeake Bay during the summer. Examination of protargol‐stained specimens revealed that these dinoflagellates also feed heterotrophically as indicated by the presence of food vacuoles containing partially digested prey. Ingested prey were generally identified as nanociliates (≥20 μm) belonging to the oligotrich genera Strobilidium and Strombidium; occasionally other small ciliates (e.g. Balanion sp. and Mesodinium sp.), dinoflagellates, and diatoms were observed in early stages of digestion. the percentage of these mixotrophs that had ingested prey was usually less than 20%, but approached 30% in some samples. Occurrence of food vacuoles in Gymno. sanguineum was positively correlated with ≤20 μm oligotrichous ciliate density; limited data for Gyro. uncatenum suggests a similar relationship, but C. furca feeding was not related to nanociliate densities.