The prevalence and implications of copepod behavioral responses to oceanographic gradients and biological patchiness

Several species and developmental stages of calanoid copepods were tested for responses to environmental cues in a laboratory apparatus that mimicked conditions commonly associated with patches of food in the ocean. All species responded to the presence of phytoplankton by feeding. All species responded by increasing proportional residence time in one, but not both, of the treatments defined by gradients of velocity or density. Most species increased swimming speed and frequency of turning in response to the presence of chemical exudates or gradients of velocity. Only one species, Eurytemora affinis, increased proportional time of residence in response to gradients in density of the water. Responses of E. affinis to combined cues did not definitively demonstrate a hierarchical use of different cues as previously observed for Temora longicornis and Acartia tonsa. A simple foraging simulation was developed to assess the applicability in the field of the behavioral results observed in the laboratory. These simulations suggest that observed fine-scale behaviors could lead to copepod aggregations observed in situ. The present study demonstrates that behavioral response to cues associated with fine-scale oceanographic gradients and biological patchiness is functionally important and prevalent among copepods and likely has significant impacts on larger-scale distributional patterns.