FEEDING BY A HETEROTROPHIC DINOFLAGELLATE (NOCTILUCA SCINTILLANS) IN MARINE SNOW

Marine snow samples were collected on two dates (20 and 27 August 1992 ) in the San Juan Islands, Washington. On both sampling dates the hete rotrophic dinoflagellate Noctiluca scintillans was concentrated in agg regates. On 20 August ''small'' and ''large'' aggregates were sampled separately. The data indicate that on this date, all of the N. scintil lans were in aggregates and that most were in the large aggregates. Ab out 60% of the N. scintillans contained food, which, given their assoc iation with aggregates, likely resulted from feeding in marine snow. O n 27 August, 51% of the N. scintillans were in aggregates and 80% of t hese individuals contained food. Only 20% of the individuals in the wa ter surrounding aggregates contained food. The data suggest that on th e two sampling dates, aggregates were the preferred habitat of N. scin tillans and that N. scintillans associated with marine snow had greate r success feeding than did individuals in the surrounding water. Durin g periods when water-column concentrations of N. scintillans prey are reduced, marine snow, with its typically high concentrations of phytop lankton, may act as a refuge habitat.