ABSTRACTThe marine chrysophyteDinobryon balticum (Schzütt) Lemm. was one of the dominant members of the phytoplankton community (1.8×103cells‐L−1) in June and July in Conception Bay, Newfoundland. Dinobryon balticumcolonies were common only in samples from June and July. The cells were concentrated at 5 m (X±SD=1.11±4 × 105cells.L−1) and at 40 m (3.32±2×104.L−1) depths. Colonies were composed of up to 560 cells with a mean (±SD) colony size of 10 ± 1 cells at 5 m and 40 ± 8 cells at 40 m. Fluorescent latex bead‐uptake experiments conducted with field samples indicated that this marine species was capable of phagotrophy and that twice as manyDinobryoncells were ingesting beads at 40 m than at 5 m, although the ingestion rates for those cells actively ingesting beads were similar at both depths. This chrysophyte was found in association with bacteria‐and nutrient‐rich microhabitats of microaggregates and fecal pellets. The cells and colonies observed in this study appeared to be healthy, as demonstrated by their appearance and their