Vertical distribution of marine particles and grazers. II. Relation of grazer distribution to food quality and quantity

Vertical distribution of zooplankton in the Southern California Bight in relation to its food, the microplankton, was examined during a 1 wk cruise when food quality did not vary within the euphotic zone. The vertical distribution of zooplankton biomass was consistently related to the vertical distribution of plant biomass, but only at night. Many of the distributions of individual species were not consistently related to the vertical distribution of plant biomass, primary productivity or phytoplankton growth rate. Of those that were, the majority were related to plant biomass, not primary productivity. Most groups of species which co-occurred in space and time were not homogeneous with respect to either species or developmental state. The daily removal of photosynthetically-produced carbon by the zooplankton was small, but not trivial. Daily water column production of carbon exceeded the community ingestion when calculated using in situ measurements of ingestion and literature values of daily ration. Although many large migratory grazers were situated within the chlorophyll maximum at night, they ingested less carbon than was produced within that feature during the day.