Light spectra regulated foraging and feeding behaviors shed light on stock enhancement of the sea urchin Strongylocentrotus intermedius

Light is an important environmental factor for the fitness of small sea urchins. It is thus important to reveal the appropriate light environments for their stock enhancement. However, the effects of light spectra on fitness related behaviors of sea urchins remain mostly unknown. To reveal appropriate light spectra for stock enhancement of the sea urchin Strongylocentrotus intermedius, we investigated the effects of light spectra on the foraging behavior, phototaxis, Aristotle's lantern reflex of S. intermedius (test diameter: 10.35 ± 0.05 mm). There were five light spectra, including red (630–670 nm), yellow (570–600 nm), green (510–550 nm), blue (440–490 nm) and white light (a mix of blue-based and a little red). We found that successful foraging proportion under blue light (65 %) was obviously higher than those under other light spectra, although no significant difference was detected (P > 0.05). The foraging time of S. intermedius was significantly higher under red light than under blue (P < 0.05) and white light (P < 0.01). Light spectra did not significantly affect the movement distance of S. intermedius (P> 0.05). Light spectra showed no significant effect on phototaxis of S. intermedius (P > 0.05). This indicates that the effect of light spectra on the foraging behavior is not due to phototaxis and movement distance in S. intermedius. Further, Aristotle's lantern reflex of S. intermedius under white light was significantly higher than that under red light (P < 0.01). In summary, S. intermedius showed significantly better foraging and feeding ability, when they were exposed to blue and white light. Since most of the spectrum is short-wavelength light (blue light) in the water below 10 m, we suggest that small S. intermedius are appropriate to be reseeded into clear water areas with the depths more than 10 m.