Light intensity regulates phototaxis, foraging and righting behaviors of the sea urchin .

Small sea urchins (1-2 cm of test diameter) are exposed to different environments of light intensities after being reseeded to the sea bottom. With little information available about the behavioral responses of to different light intensities in the environment, we carried out an investigation on how is affected by three light intensity environments in terms of phototaxis, foraging and righting behaviors. They were no light (zero lx), low light intensity (24-209 lx) and high light intensity (252-2,280 lx). Light intensity had obvious different effects on phototaxis. In low light intensity, sea urchins moved more and spent significantly more time at the higher intensity (69-209 lx) ( = 0.046). in high light intensity, in contrast, spent significantly more time at lower intensity (252-690 lx) ( = 0.005). Unexpectedly, no significant difference of movement (average velocity and total distance covered) was found among the three light intensities ( > 0.05). Foraging behavior of was significantly different among the light intensities. In the no light environment, only three of ten found food within 7 min. In low light intensity, nine of 10 sea urchins showed successful foraging behavior to the food placed at 209 lx, which was significantly higher than the ratio of the number (two of 10) when food was placed at 24 lx ( = 0.005). In the high light intensity, in contrast, significantly less sea urchins (three of 10) found food placed at the higher light intensity (2,280 lx) compared with the lower light intensity (252 lx) (10/10, = 0.003). Furthermore, showed significantly longer righting response time in the high light intensity compared with both no light ( = 0.001) and low light intensity ( = 0.031). No significant difference was found in righting behavior between no light and low light intensity ( = 0.892). The present study indicates that light intensity significantly affects phototaxis, foraging and righting behaviors of and that ~200 lx might be the appropriate light intensity for reseeding small .