THE MARINE MIXOTROPH DINOBRYON BALTICUM (CHRYSOPHYCEAE) - PHAGOTROPHYAND SURVIVAL IN A COLD OCEAN

The marine chrysophyte Dinobryon balticum (Schutt) Lemm. was one of th e dominant members of the phytoplankton community (1.8 x 10(5) cells(. )L(-1)) in June and July in Conception Bay, Newfoundland. Dinobryon ba lticum colonies were common only in samples from June and July. The ce lls were concentrated at 5 m (X +/- SD = 1.11 +/- 4 x 10(5) cells(.)L( -1)) and at 40 m (3.32 +/- 2 x 10(4.)L(-1)) depths. Colonies were comp osed of up to 560 cells with a mean (+/- SD) colony size of 10 +/- 1 c ells at 5 m and 40 +/- 8 cells at 40 m. Fluorescent latex bead-uptake experiments conducted with field samples indicated that this marine sp ecies was capable of phagotrophy and that twice as many Dinobryon cell s were ingesting beads at 40 m than at 5 m, although the ingestion rat es for those cells actively ingesting beads were similar at both depth s. This chrysophyte was found in association with bacteria and nutrien t-rich microhabitats of microaggregates and fecal pellets. The cells a nd colonies observed in this study appeared to be healthy, as demonstr ated by their appearance and their ability to ingest beads.