It’s a Christmas Miracle! 

11 November 2017

Gecarcoidea natalis, also known as the Christmas Island red crab, is a very unique species of land crab specific to an island in the territory of Australia named, Christmas Island (Parks Australia, 2014). This island is situated in the Indian Ocean where the red crabs participate in an annual mass migration from the forest to the coast, in order to breed and reproduce.

This breeding migration occurs annually during the wet season, which is from the months of October to December (Australian Government Department of the Environment, 2014). Spectacularly, as an estimated 43 million land crabs migrate to lay their eggs in the ocean, the roads on the island are closed and guarded by the authorities for at least a week to ensure the safe migration of the island crabs as shown in Figure 1 below (Parks Australia, 2014). However, it is not only the wet season that influences the commencement of their migration, it is also the different phases of the moon that serve as a contributing factors to the beginning of the crab migration. Female red crabs migrate into the sea and lay their eggs specifically and exactly at the time of the high tide on the last lunar quarter (Effron, 2013).

During the entire process of migration, the males lead the way to the coast while the females progressively follow afterwards. In the first phase, the crabs arrive at the shoreline and they take a quick dip in the sea to replenish body moisture and salts from their long journey. “The males begin to dig shallow burrows, and the females join them as the mating ritual progresses” (Christmas Island, 2014). After three days of mating, the females lay their eggs and stay in their burrows between two to three weeks as the male red crabs take another dip into the water before returning to their habitat on land (Effron, 2013). The second phase occurs at sea when the females drop their eggs and they immediately turn into larvae. After a few months of growth in the sea, they evolve in their larval stage becoming “megalops” or small baby crabs (Australian Government Department of the Environment, 2014) . The baby crabs then travel back towards the land to join and settle with the rest of the red crabs.

 The successful development of the Christmas Island Red Crabs is very unpredictable. It is incredible when large numbers of baby crabs mature and return from the sea back to their natural habitat of the rain forest, and this spurs further ecological research within this field. With more than 120 million crabs found in the rain forest of Christmas Island (Christmas Island, 2014), their variable mass breeding migration is a true depiction of a Christmas miracle.

References

• Australian Government Department of the Environment, (2014). Red crabs and migration | Christmas Island National Park | Department of the Environment. [online] Available at: http://www.environment.gov.au/resource/red-crabs-and-migration-christmas-island-national-park  [Accessed 09 Nov. 2014].

• Christmas Island, (2014). Christmas Island Tourism Association – Red Crab Migration. [online] Available at: http://www.christmas.net.au/experiences/red-crab-migration.html  [Accessed 11 Nov. 2014].

• Effron, L. (2013). Crustacean Invasion! Millions of Red Crabs Take Over Australia’s Christmas Island. [online] ABC News. Available at: http://abcnews.go.com/blogs/technology/2013/11/crustacean-invasion-millions-of-red-crabs-take-over-australias-christmas-island/  [Accessed 09 Nov. 2014].

• Parks Australia, (2014). Red crabs. [online] Available at: http://www.parksaustralia.gov.au/christmas/people-place/red-crabs.html  [Accessed 10 Nov. 2014].