November 9, 2014

1329 AUSTRALIA (Christmas Island) - The annual red crab mass migration


Located at 500km south of Indonesia, and at 1,560km from the town of Exmouth, the closest point of the Australian mainland, Christmas Island is quite isolated, so had a high level of endemism among its flora and fauna. Unfortunately two species of native rats have become extinct, the endemic Christmas Island Shrew has not been seen since the mid-1980s, while the Christmas Island Pipistrelle (a small bat) is critically endangered and possibly also extinct. Now the land crabs and sea birds are the most noticeable fauna on the island. Twenty terrestrial and intertidal species of crab have been described here, of which thirteen are regarded as true land crabs, being only dependent on the ocean for larval development.

The Christmas Island red crab (Gecarcoidea natalis) is a species of land crab endemic to Christmas Island and the Cocos Islands. It has been estimated that 43.7 million adult red crabs lived on Christmas Island alone, but the accidental introduction of the yellow crazy ant is believed to have killed about 10-15 million of these in recent years. Red crabs are rather large crabs with the carapace measuring up to 116mm wide. The male are generally larger than the females, while adult females have a much broader abdomen and usually have smaller claws. Bright red is their most common colour, but some can be orange or the much rarer purple. The annual red crab mass migration (around 100 million animals) to the sea to spawn has been called one of the wonders of the natural world. This takes place each year around November - after the start of the wet season and in synchronisation with the cycle of the moon. Once at the ocean, the mothers release the embryos where they can survive and grow until they are able to live on land.

About the stamps
The first stamp is part of a series featuring four varieties of crabs, about which I wrote here. The second stamp is part of the series Christmas Island National Park, , about which I also wrote here.

References
Christmas Island red crab - Wikipedia

Sender: ???
Sent from Flying Fish Cove (Christmas Island / Australia) on 15.07.2014
Photos: Linda Anticich

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