Crabs keep tempo with the tides
Most coastal areas experience two tidal cycles in a 24-hour period, and the animals that live on the waterfront synchronise with the 12-hourly ebb and flow in order to survive. Fiddler crabs emerge from their burrows to forage, fight and socialise when the water is at its lowest, while shore crabs prefer to come out during high tide to hide from predators under the waves.
Nerve tissue in a crab’s eyestalks called the medulla terminalis gathers information about the peaks and falls in the ocean’s journey up the beach. The eye’s activity is kick-started by an internal pacemaker in the brain that essentially works like an alarm clock that chirps when the tide is on the move. This phenomenon is still poorly understood, but laboratory experiments have demonstrated that wild-captured crabs maintain their tidal rhythms hundreds of miles away from their home beach.