March of the crabs, Pascal Kobeh, France, 2010

Pascal Kobeh/Unforgettable Behavior
October 28, 2021
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Stack of crabs underwater
Pascal Kobeh/Unforgettable Behavior

March of the crabs
Pascal Kobeh, France

Each year, thousands of deep-sea majid spider crabs walk over the seabed to shallow waters off South Australia. In their drive to migrate, they climb over each other, sometimes forming huge piles. “They walked like an army on the march,” Kobeh said. Once they arrive, many of them molt their shells. It takes a while for the new, expanded shell to harden—a vulnerable time for a crab. This may be a reason for the mass congregation, as there is safety in numbers from predators such as rays. Gatherings are also great places to find mates. However, receptive females are not always present, plus males cannot mate when they have soft shells, so the migration is still a partial mystery.

Technical specification: Canon EOS-1Ds Mark II + 15mm lens; 1/60 sec at f9; ISO 400; SEACAM housing

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