DIEL VERTICAL MIGRATION IN ZOOPLANKTON - RAPID INDIVIDUAL-RESPONSE TO PREDATORS

While diel vertical migration in zooplankton has been shown recently to be a predator avoidance behavior, the mechanism by which predators induce and maintain such behavior has been debated. We report results of an in situ predator manipulation experiment during which enclosed populations of the marine planktonic copepod Acartia hudsonica rapidly changed their vertical distribution and diel migration behavior depending on presence or absence of the planktivorous fish Gasterosteus aculeatus. These results point unambiguously to phenotypic behavioral plasticity of individual planktonic prey, not, as previously hypothesized, population-genetic level behavioral changes caused by selective fish predation, as the mechanism underlying changes in diel vertical migration in this copepod.