Sea urchin grazing can damage corals, but little is known how such damage can be remediated. We conducted three caging experiments in the field to determine the relationships among the portunid crab Thalamita prymna, the long-spined sea urchin Diadema setosum and the massive coral Platygyra carnosa. Experiment 1 showed that urchins caused coral tissue loss and reduced coral weight, and such effects were stronger at higher urchin densities. Experiment 2 showed that crabs could be effective urchin predators. Experiment 3 revealed that, when a rock with fouling organisms (an alternative food source) was available, some urchins managed to survive, but they did not cause appreciable coral damage. Together, our results indicate that, crab predation, an overlooked relationship in coral reefs, can be exploited to help control urchin corallivory and bioerosion. Prohibiting fish trapping in reef areas could reduce the by-catch of these crabs and protect reefs against urchin attack.

放牧海胆会破坏珊瑚，但如何补救这种破坏却鲜为人知。我们在该领域进行了三个笼养实验，以确定Portunid蟹Thalamita prymna，长旋海胆Diadema setosum和大块珊瑚Platygyra carnosa之间的关系。实验1表明，海胆导致珊瑚组织流失并减轻了珊瑚的重量，在海胆密度较高的情况下，这种作用更强。实验2表明，螃蟹可能是有效的海胆食肉动物。实验3表明，当一块含有结垢生物的岩石（替代食物来源）出现时，一些顽童得以幸存，但它们并未对珊瑚造成明显损害。总之，我们的结果表明，可以利用螃蟹的捕食（一种在珊瑚礁中被忽视的关系）来帮助控制海胆珊瑚和生物侵蚀。禁止将鱼困在礁区中可以减少这些螃蟹的副渔获物，并保护礁免受海胆侵袭。