Zooplankton: The Ocean Drifters

Abstract

Zooplankton comprises a highly diverse assemblage of organisms in terms of life history, body size, trophic habits, functional traits and role within the ecosystem. Spatial and temporal patterns in the distribution of zooplankton abundance and traits tend to be directed by large-scale gradients in temperature and nutrition regimes, and by recurrent oceanographic features like fronts that modulate productivity and the structure of planktonic assemblages. Zooplankton have evolved four main strategies for successful feeding on a wide spectrum of prey within a nutritionally diluted medium: passive and active ambush feeding, current feeding and cruise feeding. In most cases detection, pursuit and ingestion of prey requires a fine balancing of hydrodynamics at low and intermediate Re. The classical view of zooplankton as a simple herbivorous link between primary producers and higher order consumers within a linear trophic array has given way to a more complex depiction of planktonic food webs where mixotrophy is pervasive among the smaller components of the microbial loop, and omnivory among metazoan zooplankton, and particularly among copepods. Microbial and metazoan trophic pathways coexist, are interlinked and their relative importance is modulated by bio-physical coupling; on average, microbial grazers consume the largest fraction of marine primary production in the global ocean.