Kate Lowe, a marine photographer, captured the event with her camera. He said: “I go snorkelling most of the year round but I have never seen spider crabs in such numbers. “When we got to the beach, it looked like there were a lot of dark rocks under the surface. But it turned out there were thousands of crabs just two or three steps into the water.” He added: “It was really incredible. It was only up to the knees. I was able to float in the water above them and tried not to step on them. “Many of the tourists were screaming at the sight of them.” The mass gathering is thought to help the crabs protect themselves from predators while they wait for their new exoskeletons to thicken and harden.
Climate change makes mass gatherings common
Although it’s not unusual to see them in British waters, mass gatherings like this are becoming more common in the summer due to rising sea temperatures from climate change. The crabs are migratory and once their new shells are hard enough, they will disperse and disappear to depths of up to 300 feet, leaving Cornwall’s beaches quiet and claw-free. European spider crabs are much smaller than their famous giant Japanese cousins, with their shells reaching about eight inches in width and a claw-to-claw measurement of 20 inches. Crustaceans are common in the Mediterranean Sea and can migrate up to 100 miles over eight months. Last Thursday, a blue shark was bitten on the leg during a swim. The company behind the tour said such incidents were “extremely rare”. Crabs are not the first scourge to hit Cornish shores this summer. Last month, the Cornwall Wildlife Trust reported that hundreds of octopuses were flocking to the county’s seas and gobbling up lobsters.
