FEEDING BY THE EUPHAUSIID EUPHAUSIA-PACIFICA AND THE COPEPOD CALANUS-PACIFICUS ON MARINE SNOW

Consumption and assimilation rates of marine zooplankton feeding on la rge, abundant aggregates, known as marine snow, were measured for the first time. Two common zooplankton species, the euphausiid Euphausia p acifica and the copepod Calanus pacificus, consumed diverse types of f ield-collected marine snow, including diatom flocs, abandoned larvacea n houses, and dinoflagellate aggregates, regardless of their compositi on, C:N ratio, age, or the availability of alternate dispersed food. I ngestion rates of aggregates by E, pacifica increased with increasing marine snow concentration, although in situ concentrations of aggregat es were not sufficient to elicit a maximum ingestion rate. Ingestion r ates of aggregates by E. pacifica at higher aggregate concentrations w ere from 9 to 15 mu g C euphausiid(-1) h(-1). Assimilation efficiencie s of euphausiids grazing on marine snow were 83 % (dinoflagellate snow ) and 64 to 75 % (diatom/larvacean house snow). These results indicate that marine snow can be an important food source for marine zooplankt on and that consumption of large aggregates is likely to play a role i n the cycling of carbon and the structure of food webs in the pelagic zone of the ocean.