Negative phototaxis in crustacean larvae: Possible functional significance

Phototaxis of stage I larvae of the crab Rhithropanopeus harrisi (Gould) was quantitatively monitored by a microscope-television system. After dark-adaptation there is negative phototaxis only at the highest stimulus intensity, whereas the animals respond positively to intensities between 1.0 and 0.0006 W m-2. After light-adaptation there is positive phototaxis at intensities above 0.005 W m-2 while a negative response is observed to a lower range of intensities. Mean swimming speed during positive phototaxis does not vary with dark or light-adaptation or with stimulus intensity; however, during the negative response after light-adaptation speeds are intensity-dependent and are significantly faster at the highest response-initiating intensities than during a positive response. Arguments are presented to show that this negative response 1) may act as a shadow reflex, and 2) might be important in vertical movements. © 1974.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation