Hundreds of crabs have been spotted washed up along a Welsh shoreline. Beachgoers spotted the apparently lifeless crustaceans while walking along Traeth Mawr Big Beach, Anglesey, on Monday.
But according to experts the common spider crabs may not be dead at all. The phenomenon is more likely to be the aftermath of a mass breeding event.
A spokesman for Anglesey Sea Zoo said: "These are unlikely to be deceased crabs and more likely moults from a mass breeding event. The females can only accept sperm after they have moulted (shedding their outer shell), which leaves them extremely vulnerable to predation. To keep them safe they gather in huge numbers with the males forming a protective barrier against any would-be threats."
Following the event the discarded moults can be seen wash up on shore in large numbers. Similarly a representative for the Marine Conservation Society said although it is unclear to determine if the crabs are dead or moults from the pictures alone the latter is the most plausible scenario.
She said: "It is not clear from the images if they are moults (the shells of the animal that they shed) or dead animals. If they are moults this is a normal phenomenon for spider crab which congregate in numbers to moult, which they need to do to then enable them to breed. These could be their expelled hard shells.
"If they are dead animals we cannot comment on why this has occurred without further evidence. It is important for us to understand why these kinds of events happen and what it means for marine life around the UK."
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