Study links warming oceans to rise in dangerous shellfish toxin

January 17, 2017

A recent study has discovered a new link between warming ocean conditions and a dangerous neurotoxin, known as domoic acid, which can accumulate in species like Dungeness crab, clams, mussels and anchovy. This spells trouble for fisherman, whose livelihood may be on the line, as well as seafood lovers who could soon see a long-term threat to their seafood dinner options.

Domoic acid is a toxin produced by Pseudo-nitzschia, a micro algae that can be harmful to both humans and wildlife, including sea lions and birds. In mild cases, it can cause vomiting, diarrhea and abdominal cramps and in severe cases it leads to trouble breathing, memory loss, coma or death.

Seafood lovers got a glimpse of this in 2015, when record high ocean temperatures and lingering toxic algae blooms raised the domoic acid in shellfish to unsafe levels, shutting down the West Coast Dungeness crab fishery from Alaska to Southern California for several months. Though less dramatic, the problem emerged again this season, when harvesting was again delayed for portions of the coasts.

A recent article explains that in the case of Dungeness crabs, the food chain looks like this: The phytoplankton Pseudo-nitzschia produces the toxin domoic acid during an algae bloom. Zooplankton and filter feeders, like clams and mussels, then eat that phytoplankton. (Interestingly, not all shellfish react the same way. Mussels, for example, are able to rid themselves of the toxin within a few weeks, while domoic acid may linger in clams for several months, even up to a year.) Those delicious Dungeness crabs we like so much have a taste for clams, which is where domoic acid can be passed up the food chain to us humans.

Food safety officials are able to test for unsafe levels, keeping tainted seafood out of restaurants and away from seafood counters, but scientists haven't been able to predict when natural algae blooms may take a toxic turn — until now.

"The record of domoic acid is now 20 years long, allowing us to look at it from a different perspective than anyone has previously," Morgaine McKibben, the lead author of the new study said in the article.

The researchers looked at long-term data collected from Oregon razor clams, copepods (zooplankton that drift with the currents and are studied to predict salmon runs), and recurring climate patterns known as the Pacific Decadal Oscillation and El Nino Southern Oscillation. And they were able to establish that domoic acid events, like those that have been impacting the West Coast Dungeness crab fishery, are strongly related to warm phases in the ocean.

"The most important takeaway from the study is that it's telling us about changes in the food web based on long-term observations of changes in the oceans. It's a very zoomed out view of how the food web responds to natural changes to ocean conditions. That's very important when you talk about resource management," McKibben said. These types of long-term records are somewhat rare in oceanography, she continued, because "it's hard to find funding to keep consistent observations like this going."

And a future with more frequent domoic acid events seems likely, Bill Peterson, a NOAA senior scientist and co-author of the study said in the article. "We're having more and more of these warm ocean events and we're going to have more domoic acid blooms each year. It might become a chronic problem," he added.

That paints a troubling picture for crab fishermen like Bob Eder of Newport, Oregon, who said he worries about how future domoic acid events could impact exports — critically important to boosting the overall price of whole crabs. While Americans typically eat only the meat from the crab, Chinese consumers also eat what's known as the "butter" (or guts) of the crab, where domoic acid tends to be more concentrated.

While officials from the California Department of Public Health say they test year-round for toxic phytoplankton at more than 100 sampling sites along the entire California coastline, Peterson thinks states vulnerable to domoic acid events should be doing even more testing.

"They should sample more often and over a wider ... area," says Peterson. "Crab harvests are a huge money maker on the West Coast. You can't have people think they're going to get sick from eating crabs. Pretty soon [states] are going to have to sample more often and more places to keep better tabs on what's going on in the ocean."

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Category: Food Safety