Photophobic responses of calanoid copepods: possible adaptive value

• Published in: Journal of Plankton Research
• Main Authors: Buskey, Edward J., Mann, Christopher G., Swift, Elijah
• Format: Text
• Language: English
• Published: Oxford University Press 1987
• Subjects: Articles; Pseudocalanus minutus; Copepods
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/9/5/857; https://doi.org/10.1093/plankt/9.5.857

A genual pattern of photophobic responses has been observed which differs for calanoid copepods from freshwater, estuarine and oceanic environments. Using a video-computer system for motion analysis, the photophobic responses of light and dark adapted calanoid copepods were compared. Dark-adapted copepods were exposed to 600 ms flashes of dim blue light at 5 s intervals which simulated the flashes of biolumines-cent marine zooplankton. Light-adapted copepods were exposed to 600 ms intervals of darkness at 5 s intervals to simulate the shadows of organisms passing overhead. Four species of coastal marine copepods ( Acartia hudsonica, Centropages hamatus, Pseudocalanus minutus and Temora longicornis ) all showed photophobic responses to both flashes and shadows. These responses may have adaptive value to the copepods since they live in an environment with predators that are bioluminescent at night and cast shadows on their prey during the day (e.g. ctenophores and cnidarian medusae). Two species of oceanic copepods ( Euchaeta marina, Pleuromamma abdominalis ) showed strong photophobic responses to flashes but no response to shadows. This may correspond to the abundance of bioluminescent predators on copepods in the oceanic environment (fish, ctenophores, siphonophores, etc.) and their lack of exposure to the shadows of predators, since both these species are rarely found in the euphoric zone during the day. Two species of freshwater copepods ( Diaptomus sanguineus, Epishwa massachusettsensis ) showed no similar photophobic response to flashes of light. This lack of startle response may relate to the lack of bioluminescence in the freshwater environment. Freshwater copepods showed a weak photophobic response to shadows. The adaptive value of this behavior is unclear, however, since the responses seem to be too weak to function for escape, and the dominant predators large enough to cast shadows (fish) tend to approach their prey laterally.