Christmas Island’s annual crab migration just got a helping hand from rangers who have constructed a ‘crab bridge’ over the island’s busiest road.

Christmas Island red crab.

Christmas Island red crab. Image by John Tann / CC BY 2.0

The annual spawning season sees millions of crabs migrate from the inland forests to the coast to breed and release their eggs. As the crabs stream towards the beaches, large areas of the Indian Ocean island are blanketed in a sea of red. Inevitably, so are some sections of road.

In preparation for this mass migration, which can take up to 18 days, rangers on the 135 sq km island have set up barriers along roadsides in an effort to prevent the death of thousands of crabs by vehicles. 31 underpasses have been tunneled beneath roads along the migration route and a 5m high bridge has been constructed across the island’s busiest road to aid the safe passage of the colourful crustaceans. The combination of the barriers, underpasses and bridge is designed to funnel the crabs across the road with minimal fatalities.

And while the bridge has obvious benefits for the crabs, it has also become an unexpected tourist attraction. “Sydney can have its Harbour Bridge, and San Francisco its Golden Gate Bridge, but it’s our crab bridge which is currently wooing tourists from all over the globe,” Christmas Island Tourism Association marketing manager Linda Cash told the ABC. That might be overstating it slightly…

Spawning this season is expected to take place on 6 January, during the last quarter of the moon, the optimal time for females to release their eggs into the sea. The wave of crabs moving across the island will occur in the weeks on either side of this date, as the creatures make their way to the shore, then return to their homes in the forest.

And yet all of this effort could be for naught. Of the millions of crab larvae safely deposited into the sea, most will be eaten by fish, manta rays and whale sharks, which visit the waters surrounding the island during the crab spawning season. Baby crabs will emerge from the sea to begin their migration to the forest only once or twice a decade. But when they do, the island’s infrastructure will support their journey home.