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Rising ocean acidity bad news for West Coast’s $200 million Dungeness crab fishery

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Acidification of the world’s oceans was supposed to be a distant problem — nothing to worry about until some time in the future.

But a new study of juvenile Dungeness crab collected off the Pacific Northwest coast shows the crustaceans are vulnerable to conditions that exist right now.

Published last week in the journal “Science of The Total Environment,” the study found that tiny developing crabs sampled from coastal waters off Oregon and Washington suffered damage to their shells as well as to bristly, hairlike sensory organs believed to help them orient to their surroundings.

The findings have unsettling implications for a roughly $200 million West Coast fishery — California’s most valuable ocean crop and a key economic driver for struggling fishing ports on the North and Central Coast.

The California fleet caught more than $47 million worth of Dungeness crab last year, including nearly $5 million worth of crustaceans landed in Bodega Bay.

The new research, said veteran Bodega Bay fishermen Tony Anello, sounds “very discouraging.”

“The way I look at things right now, if I had to start in this business right now, I wouldn’t start at all,” he said grimly.

The findings are consistent with laboratory studies demonstrating ill effects on developing crabs and other shellfish from increasingly acidic conditions predicted to occur as oceans absorb ever-higher concentrations of carbon dioxide from the atmosphere.

They mark the first conclusive evidence that existing conditions in the natural environment are severe enough already in some areas to interfere with development of larval crabs, causing abnormal ridging and scarring of their external shells and legs from the corrosive effects of the water, the authors said.

“We found dissolution impacts to the crab larvae that were not expected to occur until much later in this century,” co-author Richard Feely, a senior scientist with the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory, said in a news release.

It’s also the first time scientists have seen evidence of secondary effects on the organisms’ bristly “mechanoreceptors,” which jut out from their shells and help the creatures navigate through space.

Ocean acidification — a side effect of global greenhouse gas emissions — is intensifying more rapidly on the west coast of the United States than anywhere else in the world, and particularly off California, said lead author Nina Bednarsek, a senior scientist with the Southern California Coastal Water Research Project. The worsening conditions are a function of temperature, currents and ocean dynamics, she said.

The resulting chemical changes reduce the availability of calcium carbonate, a key building block used by crab, mollusks and other organisms to build strong, hard shells and other organic structures.

It also corrodes calcified shell material and, in the case of the nearly translucent, juvenile Dungeness crabs, appears to destabilize the anchors that attach their sensory receptors in some cases, causing them to fall out, researchers said.

Those crabs showings signs of shell dissolution also were smaller overall than their counterparts, according to the study.

The concern is that affected crab will have developmental delays, difficulty swimming and regulating buoyancy and spatial position, as well as increased energy demands and generally impaired survival.

Bednarsek said the study raises myriad questions about the impacts of acidic water on crabs at other life stages, as well as on other organisms. But the fact that it appears to effect the animals through multiple pathways is alarming, Bednarsek said.

Tessa Hill, a marine scientist at the UC Davis Bodega Marine Lab and member of the Bodega Ocean Acidification Research group, said the new research “is very significant, in that it’s on Dungeness crab, which is a commercial but also a culturally important species in California.”

She pointed particularly to part of the study that indicated effects on the crab shells may have begun occurring as long as two decades ago, growing worse over time by almost 10 percent.

Bodega Marine Lab scientists have been studying locally, commercially raised oysters and native mussels and other mollusks on the California coast, discovering that changing water conditions have resulted in thinner, weaker shells and smaller organisms going back as far as 10 years.

“It’s a very consistent story across these groups that we’ve researched,” she said.

Noah Oppenheim, executive director of the Pacific Coast Federation of Fishermen’s Associations, called the new research “a major warning sign” that failure to reduce to curb carbon emissions could lead to “catastrophic economic impacts.”

It foretells longterm environmental change that is often difficult for already burdened commercial fishermen to track, Oppenheim and others said.

“Whether it will impact us later, I would imagine it probably would,” said longtime fisherman Dick Ogg, vice president of the Bodega Bay Fishermen’s Marketing Association and a member of the Cordell Bank Marine Sanctuary Advisory Council. “But right now, that’s probably the furthest thing from the guys’ minds.”

Instead, the local fleet is focused on how the current crab season is unfolding, and what they can anticipate on developing rules governing protections for migrating whales.

“That’s the five-alarm fire that’s raging right now in coastal communities up and down the coast,” Oppenheim said. “A new, small brush fire 10 years out on the horizon is important, but that’s certainly not attracting much interest and attention.”

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

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