MEPS 177:157-163 (1999)  -  doi:10.3354/meps177157

Reduction of grazing activity of two estuarine copepods in response to the exudate of a visual predator

Matthew D. Cieri*, Donald E. Stearns**

Department of Biology, Rutgers University, Camden, New Jersey 08102, USA
Present addresses:
*School of Marine Sciences, University of Maine, Orono, Maine 04469, USA. E-mail:
**Department of Biological Sciences, Wagner College, Staten Island, New York 10301, USA

ABSTRACT: A grazing zooplankter may minimize its susceptibility to visual predation by reducing its gut contents or its feeding movements. Such behavioral mechanisms require (1) that the prey can detect the predator and (2) that it reduces its grazing activity when light conditions favor visual predation. In this work we have examined the grazing activity of 2 estuarine copepods, Acartia tonsa and Acartia hudsonica, in the chemical presence or absence of its natural visual predator, the Atlantic silverside Menidia menidia. Our results indicate that in the presence of chemical exudates of M. menidia, A. tonsa and A. hudsonica reduced their gut fullness. This response was observed only when light levels were high enough for visual predation. Reduction in gut fullness resulted from decreased ingestion rates, not from changes in gut evacuation rates. Light intensity was found to affect the grazing response to the fish-exuded chemical(s). Such behavior may be advantageous to these copepods in estuaries which contain large numbers of visual predators.

KEY WORDS: Acartia tonsa · Acartia hudsonica · Menidia menidia · Visual predation · Nocturnal feeding · Copepod grazing · Copepod behavior · Fish exudates

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