Effects of Competitors, Predators, and Prey on the Grazing Behavior of Herbivorous Calanoid Copepods

Gut fluorescence was measured to test the effects of potential competitors, predators, and alternate animal prey on the short term (1.5–2 h) herbivorous feeding rates of the marine calanoid copepods Calanus pacificus Brodsky, Pseudocalanus minutus (Kroyer), and Metridia pacifica Brodsky. The diatoms Thalassiossira weissflogii and Coscinodiscus perforatus were used as food. The presence of the predatory copepod Euchaeta elongata Esterly affected the swimming behavior and caused a significant reduction in the gut fullness of Pseudocalanus. Neither the presence of conspecifics nor other herbivorous grazers affected the gut fullness of any of the copepods. Feeding on algae by the omnivore Metridia was not significantly affected by the presence of Artemia nauplii as alternate prey, despite the fact that Artemia were ingested along with algae.