SAN DIEGO — Tuna crabs are swarming off the coast of San Diego. Sometimes called 'red crabs,' they have quite a few nicknames and typically live in deeper waters near Mexico.
Tuna crabs
“We humans breathing air don’t often see them. It’s kind of special when snorkelers and free divers see them right here on our beaches,” said Charlotte Seid, Senior Museum Scientist at the Benthic Invertebrate Collection for Scripps Institution of Oceanography.
When she heard that the tuna crabs had come to town, she threw on her scuba tank and dove the Scripps Canyon off La Jolla Shores to get a glimpse for herself.
“It was interesting for me personally as a recreational scuba diver to see so many of them alive, seeing them interacting with other species,” said Seid. "Recently I saw a little baby octopus chewing on a dead one, so kind of keeping that food chain going.”
Why they're here
Usually found off the coast of Baja California in Mexico, it’s more of a rare appearance here in San Diego. Experts say they’re brought here by currents set off by El Niño.
“In general, they seem to be riding up here on masses of water from Mexico," said Seid. “They spend some of their life swimming in the water column. They’ll also sit on the sea floor."
In 2015, they turned up here in massive numbers. CBS 8 was there in Ocean Beach when droves of them showed up along the shoreline.
"There was a mass stranding," said Seid. "They generated a lot of attention, and since then San Diegans have been paying a lot of attention to this species.”
Seid manages around 1 million preserved animals for the benthic invertebrate collection.
“Every specimen could be a part of this time capsule, showing us how life on Earth has changed, so every pickle jar of mine tells a story,” said Seid.
Photos: Tuna crabs swarm San Diego
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Scientifically called Grimothea planipes, tuna crabs are a species of squat lobster, but they're also known as pelagic red crabs or langostilla in spanish. Seid told CBS 8 why they're commonly called tuna crabs.
“Sometimes we want to say something about their life, how they relate to human uses, so ‘tuna crabs’ shows that they’re food for tuna, that’s something that many humans care about, and ‘crab’ is kind of a loose term,” said Seid.
They mostly eat plankton, algae, and some other invertebrates, but according to Seid, they'll eat just about anything.
“They’ll also eat each other if they have to, so we’re seeing some tuna crab cannibalism happening. In that way, it kind of keeps the population in check,” said Seid.
If you want to see them, you may want to hurry. When they're here in San Diego, it's usually during the springtime, and according to Seid, they could be gone by the end of June.
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