ABSTRACT: Consumption and assimilation rates of marine zooplankton feeding on large, abundant aggregates, known as marine snow, were measured for the first time. Two common zooplankton species, the euphausiid Euphausia pacifica and the copepod Calanus pacificus, consumed diverse types of field-collected marine snow, including diatom flocs, abandoned larvacean houses, and dinoflagellate aggregates, regardless of their composition, C:N ratio, age, or the availability of alternate dispersed food. Ingestion rates of aggregates by E. pacifica increased with increasing marine snow concentration, although in situ concentrations of aggregates were not sufficient to elicit a maximum ingestion rate. Ingestion rates of aggregates by E. pacifica at higher aggregate concentrations were from 9 to 15 µg C euphausiid^-1 h^-1. Assimilation efficiencies 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 zooplankton and that consumption of large aggregates is likely to play a role in the cycling of carbon and the structure of food webs in the pelagic zone of the ocean.

KEY WORDS: Marine snow · Grazing · Euphausia pacifica · Calanus pacificus

Published in MEPS Vol. 170 (1998) on September 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998