Ocean heat wave brought 67 rare, warm-water species to North Coast

An extended ocean heat wave that spurred a series of ecological anomalies off the Northern California coast - including toxic algae, mass sea lion strandings and the collapse of the bull kelp forest - also promoted the northward migration of an unprecedented number of southern, warm-water species.

Sixty-seven rare, warm-water creatures, including 37 whose presence has never been documented so far north, were found in the region and points poleward, according to a UC Davis Bodega Marine Laboratory study published Tuesday in “Scientific Reports.” Everything from bottlenose dolphins to two kinds of sea turtles to barnacles and small sea snails were present during the study period between 2014 and early 2017.

One colorless, tiny snail cousin, the striated sea butterfly, hadn’t previously been seen north of the tip of Baja California. It turned up in sampling nets collecting whatever critters might be floating past the Bodega Bay lab, said lead author Eric Sanford, a UC Davis professor of ecology and evolution.

Similarly, pelagic red crabs - four still alive at the lab - that came ashore at Salmon Creek Beach in January 2017 normally would have been closer to Baja, he said. Also found in the bay was the molted shell of a spiny lobster more common in Baja.

With the planet and the ocean warming, the recent, extended marine heat wave “provides a glimpse of what the Northern California coast might look like in the future,” as species move toward cooler environments to survive, Sanford said.

“We’re basically seeing these communities change before our eyes as more southern species become part of these communities,” he said. “That’s pretty dramatic.”

Most of the newcomers stayed temporarily in the north, departing the region once the water cooled. But a few stuck around off the Sonoma Coast, including the delicate-looking glass-spined brittle star - a leggy, bristled creature measuring about 2 inches tip-to-tip with deep orange markings that can still be found in local tide pools, researchers said.

Local tide pool explorers also might find for the first time blue-spotted chocolate porcelain crabs and sunburst sea anemones, which have radiating lines from their central discs, Sanford said.

Though marine heat waves already have increased in frequency and duration over the past century, the study period covers what’s believed to be the largest on record. It began with the formation of the “warm blob” in the winter of 2013-14 and later was reinforced by a strong El Niño driven north from the equatorial Pacific, according to the report.

What started as a persistent area of unusually warm water in the Gulf of Alaska expanded and spread south along the West Coast, raising water temperatures as much as 7 degrees and causing widespread upheaval.

While on land, Californians suffered unprecedented drought, the cold, nutrient-rich upwelling that traditionally makes the waters off the North Coast among the world’s most productive shut down. Reduced ocean circulation and warmer temperatures diminished the availability of tiny organisms that form the basis of the food web.

Scientists linked shifting migration patterns and mass mortality events among at least two kinds of seabirds to diminishing food supplies. Mass starvation also was evident among juvenile California sea lions. They were stranded by the thousands by mothers who, it was believed, could not find sufficient forage to feed their dependent offspring.

Off the North Coast, a persistent bloom of toxic algae unprecedented in its scope and duration closed the commercial crab fishery for more than four months because of concerns about a naturally occurring neurotoxin called domoic acid that was poisoning sea lions and other pinnipeds.

Those were short-term consequences compared with what was occurring in the North Coast’s iconic bull kelp forest, which was succumbing to a succession of radical environmental stressors.

Those changes so disrupted the forest’s ecological balance that the kelp, abalone and sea star populations all collapsed and gave way to hordes of tiny purple urchins.

At the same time, warming conditions combined with frequent reversals in the usual southward coastal currents opened the door to southern neighbors to migrate north, Bodega Marine Lab researchers said.

Not only was the warmer water more hospitable for them, but southern marine animals with larval or planktonic juvenile forms that would drift about the water anyway could make the journey without any effort once the current shifted northward, they said.

Among those that came north were a half-dozen species of nudibranch, soft-bodied gastropods that often come in fantastically bright colors and florid shapes.

“So many of the species that shifted are beautiful and amazing and offer lots of different stories,” said Jacqueline Sones, one of the study’s co-authors and research coordinator for the Bodega Marine Reserve.

The study was focused primarily on the area between Point Reyes and Point Arena. It’s an especially interesting and appropriate region because of its location just beyond Monterey Bay, which marks the outer range of many warm-water species that might be comfortable in, say, Baja, Sanford said. The Sonoma Coast was far beyond their normal range.

Researchers found a total of 37 species whose geographic ranges usually don’t reach into Northern California; 21 southern species with very rare prior records of sightings in northern reaches; and nine species that have been observed in the northern part of the state but were found in much larger abundance during the extended heat wave.

Most of the other species were found in surveys of sandy and rocky shoreline between Point Reyes and Point Arena, though unusual sightings from other some other sources both at the lab and elsewhere were included.

Seeing “such a broad range of animals” respond to changing conditions also suggests the readiness with which nature is primed to react to what may be coming, Sanford said.

“These extreme marine heat waves have the capacity to change the species in the community quickly,” Sones said. “It isn’t a response to a gradual increase in temperature. It’s a fast response to an extreme event and the magnitude of the event.”

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