Behavioral Responses of Oceanic Zooplankton to Simulated Bioluminescence

A defensive function often has been suggested for the bioluminescence of dinoflagellates and copepods, but there is only limited experimental evidence. Using closed circuit television equipment and infrared illumination we have recorded the behavioral responses of planktonic copepods, ostracods, polychaetes, chaetognaths, and euphausiids to simulated bioluminescent flashes. The swimming patterns of these organisms were then quantified using a video-computer system for motion analysis (the Bugwatcher). The photophobic response exhibited by certain copepod species in response to simulated dinoflagellate flashes, as well as the lack of response by several potential predators on copepods to their simulated bioluminescence, provide new insight into the roles of bioluminescence in plankton ecology. Comparison of the responses of the non-bioluminescent copepod Calanus finmarchicus and the bioluminescent copepod Metridia longa to simulated copepod bioluminescence show that Metridia is much more responsive than Calanus. This suggests that bioluminescence in Metridia may be recognized as a warning signal by conspecifics in addition to serving as a defense against predation.