Crabs keep tempo with the tides

World of Animals - - Animal Clocks -

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.

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