A visit to the tropics would not be the same without seeing palm trees and coconuts along the beach. Palm trees are home to a lot of different animals but one in particular stands out. The coconut crab (Birgus latro) is the largest land living arthropod in the world and is related to the hermit crab. It is also known as the robber crab or palm thief.
These crabs are known for climbing up a palm tree holding a coconut. Using their strong legs, they drop the coconut to the ground to open the husk and access the coconut flesh. Getting down is no problem because the crab simply drops off the palm tree, surviving falls of at least 4.5 m unharmed.
Its only similarity to the hermit crab involves inhabiting snail shells to protect their soft bodies as juveniles. But as an adult, the coconut crab discards the shell to develop a tough exoskeleton. This is the reason why coconut crabs grow so large, with leg spans of 1 m and body lengths of 40 cm.
Coconut crabs populate the islands around the Indian Ocean and central Pacific Ocean, especially where coconut palm trees grow. Not much information is known about these populations, with the IUCN listing the species as being ‘Data Deficient’. Conservation plans are underway to protect the coconut crab to develop a better understanding about their ecology.
Coconut crabs live in burrows and rock crevices, lining them with coconut husks. Their large pincer claw blocks the entrance to maintain a moist environment. Their burrow protects them while moulting their exoskeletons for 3 to 16 weeks or to reduce water loss from heat during the day.
Coconut crabs have no natural predators, aside from humans and other coconut crabs. Some studies have suggested their activity is affected by the presence of humans. Instances of crabs being attacked by rats on some islands has been reported, but coconut crabs also kill and eat rats. Apart from coconuts and rats, the crab’s diet includes, fruit, nuts and carrion. They use their strong sense of smell to locate food.
Coconut crabs live on the land all their lives. During mating season the female returns to the beach during high tide to release her fertilised eggs. Once hatched, the larvae experience several stages of development while in the plankton, and are prey for many animals.
After several weeks, the juveniles drop to the sea floor and return to the shore, where they find an empty snail shell or broken pieces of coconut shell as shelter. They gradually lose the ability to live in water and reach maturity after 5 years. The coconut crab can live for quite a long time, nearly 60 years.
Written by Gabrielle Ahern
Salty Wave Blue – Into all things ecology.
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If you would like to see images of animals in their marine environment, especially coconut crabs and hermit crabs, please take a look at my Pinterest site: https://www.pinterest.com/saltywave
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