Red crabs deposited on Sonoma Coast by unusual ocean conditions

BODEGA BAY - A small bunch of tiny red crustaceans that ought to be hanging out a thousand miles south of here came ashore on Salmon Creek Beach last week, the final remnants, it seems, of a wave of southern species brought north by unusually warm ocean conditions over the past few years.

The 18 pelagic red crabs now living at the UC Davis Bodega Marine Lab are the first ones reported this far north since 1985, when an isolated sighting was recorded in Fort Bragg, according to Eric Sanford, a UC Davis professor of evolution and ecology.

But those who follow life along the Pacific Coast may recall seeing images of the spidery, vermilion-colored creatures as they came ashore by the thousands last year in Monterey and a year prior, when beaches on both the Central Coast and in and around Orange County were covered in blankets of bright red crabs.

At the time, ocean waters were atypically high, a result initially of a phenomenon called “The Warm Blob” and then an ensuing El Niño ocean warming phase of record strength.

The surprise in finding the rare crabs off the Sonoma Coast at this point in time is that the ocean waters have cooled significantly over the past nine months or so, when the latest El Niño dissipated, Sanford said.

“They're more often found in southern and central Baja, off of Mexico, and it's very rare to see them even in the state of California,” Sanford said.

Seeing them now “is just another indicator of how strong that El Niño was,” he said.

The red crustaceans resemble small lobsters, with bodies about the size of a woman's thumb and two clawed appendages that extend out in front, in addition to six limbs covered in hair-like bristles. A single specimen can fit in a human hand.

Their bulbous black eyes make them look almost cute, like a character out of a Disney movie. “They're very charismatic little crabs,” Sanford says.

The crustaceans have flat tails curl under their bodies except when they swim - which they do by flipping their tails out and back, and shooting backward through the water, their appendages all squeezed together in a streamlined position.

“They're really pretty amazing,” said Jackie Sones, a research coordinator for the Bodega Marine Reserve who, with Sanford, found the crabs, three of which were later determined to be carrying eggs the two ecologists hope to see brood.

Sometimes called “tuna crabs” because they are such an important food source for the popular fish, pelagic red crabs typically live in the open ocean off the coast of central and southern Baja, occasionally pushing north during an El Niño period.

But conditions along the Pacific Coast have been highly unusual of late, beginning in late 2013 and into 2014, when a warm area of ocean water off the coast of Alaska, nicknamed the Warm Blob, intensified and spread down the whole western coast to Mexico, causing significant ecological disruption.

Food systems and fisheries were thrown out of whack as myriad species that normally stay in more southerly waters followed warm currents northward.

Sanford and Sones are interested in the study of factors that determine the outer limits of wildlife ranges. They had been documenting everything from colorful sea slugs, called nudibranches, to fish, seabirds and marine mammals that had been turning up off the North Coast during this time frame, listing at least 25, Sanford said.

They've made a habit of walking Salmon Creek Beach a couple of times a week to survey for unusual species. They found a few random claws and other pieces of what appeared to be pelagic red crabs in October 2015, February 2016 and earlier in January.

But Jan. 23, around dusk, was the first time they found whole crabs, 19 of them scattered across perhaps a few hundred yards and just washed ashore, likely brought landward by extremely high surf in the preceding days.

It was lucky they found them when they did, given what “tasty morsels” they are to so many types of animals, Sanford said.

All were alive, though one has since died, they said.

Another specimen was found on Salmon Creek Beach on Friday by a volunteer beach monitor.

There also have been four reported sightings of pelagic red crabs over the past month in the Point Reyes National Seashore, San Francisco Bay and Pescadero, on the San Mateo coast, though none farther north, according to iNaturalist.org, where people report such things.

The same day they found the red crabs, Sones and Sanford found six tiny, tropical purple sea snails that also are what Sanford called “another of those southern stragglers hanging around up here, even though El Niño ended last spring.”

The snails, about 3,000 of which were collected on the Sonoma Coast last year, are unusual in that they spend much of their life hanging upside down, suspended from the water surface by bubble formations they make with mucous secretions.

“Whether you're a marine biologist or just a casual beach walker, it's been a really fascinating time to see these southern species that you don't normally see in the wild up here in Northern California,” Sanford said.

For more on these unusual visitors or to report additional sightings of pelagic red crabs see Sones' blog, “The Natural History of Bodega Head,” at bodegahead.blogspot.com.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.