Every year in late spring, Australia’s
Christmas Island becomes
covered in crabs when the more than 40 million red crustaceans that
call the northwest island territory home start their annual
migration to the sea, covering the landscape in a mass of crimson
claws.
The migration starts with the first heavy rains in October,
November or December. At that point, there’s enough moisture in the
air for the large crustaceans, which can reach up to 11cm across,
to make the arduous, five-day journey from their homes in wet
inland forests to the Indian Ocean, covering up to 9km along the
way.
With so many of the creatures on the move, Parks Australia works
before and during the migration to protect the crustaceans by
closing roads, building fences and constructing underground
tunnels. Drivers are encouraged to stop for the crabs.
Upon reaching the sand, the male crabs dig burrows and fight each
other for ownership of the shelters. When the female crabs arrive
(usually five to seven days after the first males), they begin to
mate, and the females stay in their beachside burrows until the
last quarter of the lunar cycle. The females always wait for the
first day of the last quarter – regardless of when they started the
migration – to spawn and release their eggs into the sea.
Researchers speculate that since this phase of the moon has the
least sea level change between high and low tides, the eggs have
higher chances of survival.
This year, the possible spawning dates (and dates of the quarter
moon) are 28 November or 28 December, so the initial migration will
happen seven to 18 days before, depending on the weather. The crabs
tend to be on the move in the morning and early evening when the
air is cooler, but any dry spells will halt the migration until
wetter weather prevails.
