Spatial and temporal feeding patterns of copepods from the North Pacific centra gyre

Abstract

Spatial and temporal feeding patterns (determined from an index of gut fullness) are described for 10 typical species of calanoid copepods collected from the North Pacific central gyre (September 1968 to June 1977), an area where the zooplankton is food limited and there were a-priori reasons to suspect that feeding and competition for food were important in regulating zooplankton community structure. Over 100 samples from 11 cruises to the eastern part of the gyre were examined, and patterns of gut fullness were related to environmental variables and the copepod species structure. The copepods studied all tended to be omnivores and food generalists. Males had lower indices of gut fullness than females but both males and females of a species had similar spatial and temporal feeding patterns. Guts were usually fuller at night than during the day, even in nonmigrating species; however, within nighttime depth distributions, no depths were preferred for feeding. There were also differences between species in mean gut fullness, but different species tended to have similar spatial and temporal feeding patterns. There was considerable spatial variability, and locales could be identified in which most species had higher indices of gut fullness. The copepods were not necessarily more abundant in these locales, nor did these tend to be areas of above average chlorophyll concentration. These patterns were consistent with relatively nonselective feeding, and there was no evidence that these species separate their niches by feeding at differing places or times.