Searching for the Sea

A red tide flows from the forest to the sea. It is fall on Christmas Island in the Pacific Ocean. That’s when millions of red crabs migrate. They skitter to the sea to release their eggs. How do they know what to do?

Their timing is linked to rain. The island’s wet season begins in October. The crabs abandon their rain forest burrows. Males travel to the ocean in great numbers. They dig deep burrows and wait for the females to arrive. They mate in or near the burrows. Then the males return to the forest.

The crab migration is also linked to the phases of the moon. During the last quarter of the moon, at the turn of the high tide, the females release their eggs into the ocean. This ensures that most of the eggs reach deep water. Then the females return to their homes. The young grow up in the sea and come to land as adults.