Dive shops have been enjoying the claw-some spectacle of thousands of tuna crabs swarming off the coast of La Jolla, California during a phenomenon that’s being called the ‘crabocalypse’.
“It’s a total extravaganza out there right now,” says Zach’s Scuba Shack on Instagram; a scuba centre that takes guests on night dives to see the tuna crab invasion. “This is the craziest I’ve ever seen them, the most I’ve ever seen."
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The company’s owner, Brian Zach, first experienced the tuna crab invasion in 2019. "The truth is, nothing anyone would have told me would have prepared me for what I was about to experience,” he says on the Zach’s Scuba Shack website.
“At about 15 feet the swarm began and it only got denser the deeper we went. At about 60 feet, the group was piling on top of itself and blanketed the ocean floor for as far as my visibility allowed.”
Also known as pelagic red crabs, tuna crabs (Pleuroncodes planipes) are actually a type of squat lobster. Usually found off Baja California in Mexico, warmer waters have brought them to Southern California since around 2014, often during years when there has been an El Niño.
“It has been unusual to see them in these numbers year after year," Charlotte Seid, manager of the benthic invertebrate collection at the Scripps Institution of Oceanography at UC San Diego told NBC 7 San Diego. "It's not that the crabs are deliberately making their way to us," she says. These weak swimmers get swept along in the current.
“These have been known to drift all the way to Oregon in years prior,” says Zach.
Tuna crabs got their name because tuna love to feed on them but so do lots of other animals, including octopus, crabs, horn sharks, stingrays and spiny lobster.
“They fulfil a really important ecological niche,” says Zach. Feeding on plankton and other tiny organisms in the water, they provide an important food source for a wide range of animals higher up the food chain. “There’s even a bat in Mexico that has been known to have tuna crabs in their diet so these guys get around,” he says.
What makes the sudden arrival of the tuna crabs even more special is the knowledge that they’ll be gone in a flash. “They’re all eating each other right now and all the predators are picking them off,” says Zach. “And they’ll probably wash ashore here and be gone in a couple of weeks.”
Images and videos: Zach's Scuba Shack
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