The Christmas Island Red Crab migration. The population in the tens of millions of crabs migrate annually from the uplands to the shore of the island. They mate and if the conditions are favorable the females release their eggs (up to 100,000 per female) into the ocean. The crabs then return to the forest where they live.
Threats to the crabs include roads and vehicles and the invasive yellow crazy ant. The ant is responsible for the decline of crabs by the millions.
The crab is a keystone species on the island, dispersing seeds and turning over the soil. The loss of crabs has already shifted the composition of the plant community on the island.