UCB Moorea Class: Biology and Geomorphology of Tropical Islands

The tropical sea urchin genus Diadema, is considered one of the most significant and abundant. Their population dynamics greatly influence the health of coral reefs. Diadema have anti-predator behavior and defenses that help them to maintain a stable population. I investigated the limited spatial vision in Diadema savignyi, by testing their directional orientation to a target representing a crevice space used to hide from predators. This is the fourth sea urchin echinoderm to demonstrate evidence of spatial vision, the first for the genus Diadema. Furthermore, my results demonstrate that D. savignyi use their spines to filter light to improve their spatial vision. D. savignyi which had their spines removed lost their spatial vision. However, in starting closer to the target, D. savignyi still oriented without spines, suggesting spatial vision is still possible. In a field and lab study on the emergence times of D. savignyi, I found that D.savignyi may use daylight levels as a cue in their nocturnal emergence, usedto avoid their diurnal predators. The pervious understanding that Diadema react and process light supports my evidence of the role of light in emergence. My results illustrate mechanisms for which D. savignyi specifically are able to avoid predators, but also suggest the presence of such mechanisms in other sea urchins. In understanding these mechanisms of defense, it is possible to better understand the maintenance of sea urchin populations and thus their role in coral reef ecosystems.