Photoresponses of the copepod Mesocyclops edax

The predatory copepod Mesocyclops edax is an important component of many zooplankton communities where it typically makes extensive did vertical migrations. To describe the effect of light on adults we measured their photoresponses in the laboratory. The response spectrum is characterized by a wide plateau of greatest sensitivity from about 480 - 580 nm. These animals are adapted to perceive light during the day since their region of maximum sensitivity overlaps the spectral region of highest quantal intensity underwater (575 - 700 nm). The threshold intensity for positive phototaxis by dark adapted animals was about 5 × 10-1 Wm-2 at 540 nm, and they were positively phototactic up to an intensity of 5 × 10-1 Wm-2. Above this intensity phototaxis is no longer observed. Light-adapted animals were less sensitive than dark-adapted, but their general pattern of response to light intensity did not differ. There is no rhythm in phototaxis. Their photoresponses may provide a mechanism for controlling vertical migration so as to minimize exposure to planktivorous fish. © 1983 IRL Press Ltd.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation