Christmas Island’s red crabs have begun their annual breeding migration! This follows heavy and sustained island wide rainfalls over the last few days.
At the beginning of the wet season (usually October – December), most adult red crabs suddenly begin a spectacular migration from the forest to the coast to breed and spawn (release their eggs into the sea). The breeding migration is usually synchronised island-wide. The crabs need moist overcast conditions to sustain them during their often long and difficult journey to the sea.
The crabs time their migration to align with the phases of the moon. It all leads up to the female crabs spawning on a receding tide before dawn, during the last quarter moon phase.
The crabs are aiming for an anticipated spawning date around 6 January so if the rain persists they have plenty of time. If the rain keeps up they will continue their slow march, but if the rain stops so will the migration.
The males lead off the migration and are joined progressively by females. When they reach the sea they will dip to replenish moisture and salts and the males will dig breeding burrows. After mating, the males will begin their return migration. The females will remain in the burrows to brood their eggs for 12-13 days, before emerging from the burrows to spawn.
For the crabs to meet the spawning date they will have to have completed their mating by Christmas, so keep your fingers crossed for some good rain!
The eggs hatch into free swimming larvae immediately after they are dropped into the sea. The larvae grow through several stages in the ocean for more than four weeks before emerging from the sea as tiny crabs. The return of baby crabs is not garanteed; many years none or very few emerge from the ocean but when they do return in high number it is a spectacular event. Check out the videos below to get a glimpse of the event on a small scale.
To protect the migrating crabs, several roads have been closed in the national park and other areas on the island.
Max, Christmas Island National Park
Watch: Red crabs migrating
Watch: Baby red crabs