Researchers have identified the microscopic algae,<em> Pseudo-nitzschi, </em>which was responsible for the closure of California’s Dungeness crab season in 2015. (Courtesy C.J. Wingert, San Francisco State University)

Researchers have identified the microscopic algae, Pseudo-nitzschi, which was responsible for the closure of California’s Dungeness crab season in 2015. (Courtesy C.J. Wingert, San Francisco State University)

A microscopic killer lives in SF’s waters

Researchers find ocean acidification threatens local fisheries


Outside the Golden Gate Bridge, in California’s coastal waters, lives a killer much smaller than the Great White shark.

A certain microscopic algae, termed Pseudo-nitzschia diatoms, generate a neurotoxin called domoic acid. These diatoms bloom naturally during the spring and summer and can poison marine life and humans that consume contaminated fish and shellfish. While blooms typically disappear by fall, a massive one persisted much longer in 2015 and was responsible for the closure of California’s Dungeness crab season.

Now, new research offers proof that this “abnormal” will happen more in the future, thanks to climate change.

“We know that this particular species will grow faster when waters are warmer,” William Cochlan, a senior research scientist and biology professor at San Francisco State University, told me. “But none of the studies that have been published to date have examined whether the cells actually produce more deadly neurotoxin with increasing water temperatures or the other environmental factors that are changing in the ocean.”

A new study by Cochlan and his former graduate student Charles Wingert fills this information gap. Despite funding limitations and pandemic-related laboratory closures, the team is conducting carefully designed experiments to assess the impact of ocean acidification on the species. They found that as the ocean absorbs more carbon dioxide, corresponding increases in acidification levels will make the algae produce more toxins.

These results, which the journal “Harmful Algae” will publish later this month, highlight the importance of reducing atmospheric carbon dioxide, as well as conducting more robust scientific studies. Very little is known about this tiny killer even though its effects on marine mammals, birds, public health and the economy have been huge. Better investments in science can help communities along the West Coast better adapt to these impacts.

San Franciscans may remember the 2015 bloom. The event closed major commercial and recreational fisheries in California, Oregon and Washington, including Dungeness crab. It was disappointing for those excited about traditional Thanksgiving crab feasts and devastating for fishermen. Sea lions, brown pelicans and other marine life that ate contaminated shellfish got sick and many died. At the time, scientists believed the event offered a glimpse of a future with climate change.

The new research offers proof. Using live specimens from the 2015 bloom, Cochlan and Wingert mimicked the dynamic and multifaceted California coastal environment in research labs at the Estuary & Ocean Science Center in Tiburon. This means they had to replicate the “boom and bust” bloom situation that occurs as deep, nutrient-laden and carbon dioxide-rich waters upwell to the surface in the spring and summer.

Looking at ocean acidification in combination with other factors was not an easy task before the pandemic. And when their labs shut down due to COVID-19, the team struggled even more to keep specimens viable and the experiments on course.

“We’ve been working like dogs,” Cochlan told me. “But if we’re going to forecast the future ocean, we need to do these sort of exacting lab experiments. The alternative is to just watch and see what happens and that hasn’t worked out very well so far.”

The hope is that these new scientific results will help policymakers become less reactive to the impacts of climate change and more proactive. There are not many studies on ocean acidification and the impacts it will have on species — specifically, microscopic algae and the ones that produce toxins. Scientists can use this research to better model when and where toxic blooms may occur, which will benefit shellfish growers, fisheries, wildlife and our health.

“This is exactly the data we need to move forward,” Raphael Kudela, a professor in the Ocean Sciences Department at the University of California Santa Cruz, told me. “More information is super useful for not being so binary and being more nuanced.”

Although San Francisco and California have long recognized climate science, it’s taken federal and international governments longer to take the necessary steps to wean society away from fossil fuels. At this point, a warmer and more unpredictable future is inevitable. Investing in science can not only help us better adapt, but it could also keep Thanksgiving Dungeness crab feasts a tradition for more generations of San Franciscans.

Robyn Purchia is an environmental attorney, environmental blogger and environmental activist who hikes, gardens and tree hugs in her spare time. She is a guest opinion columnist and her point of view is not necessarily that of The Examiner. Check her out at

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