Okinawa Churashima Foundation RESEARCH INSTITUTE

Research on marine organisms

Paper published on the astonishingly strong claws of coconut crabs.

Coconut crabs are the largest terrestrial crustaceans, they inhabit tropical and subtropical areas of the Indo-Pacific, but their population has declined globally due to habitat loss and human predation. However, due to the protected environment of Ocean Expo Park, it has become the world’s northernmost breeding ground for coconut crabs, and various ecological surveys have been conducted over the past ten years.

In this study our research group analyzed the claws of the wild coconut crabs that inhabit Ocean Expo Park. We found that the strength of their claws can be nearly 90 times stronger than their weight, and the larger crabs have stronger grips. The largest coconut crab weighed 4kg and its grip strength was 3300 newtons (337kgf). The strength of their claws is the strongest among crustaceans and similar to the strength of a lion’s bite.

Coconut crabs come from the same family of terrestrial hermit crabs as Coenobita cavipes a species that carries no shell. They have no shells to protect them from predators, so it is thought they developed strong claws to use as tools and to help protect themselves. Also as coconut crabs are omnivores, they can feast on the pith of a hard coconut by using their strong claws to open the fruit. In this way it is thought that the ecology of coconut crabs is very much tied to the strength of their claws.