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USC Sea Grant researchers find toxic algae thrives in a warmer ocean, a new challenge to healthy coastal habitats

Charlotte Stevenson, Science Writer, USC Sea Grant

It was hard for many West Coasters not to feel like they were part of an Armageddon-like movie scene as they spent the summer of 2015 watching hundreds of thousands of seabirds dropping dead from starvation, record whale deaths and entanglements, record deaths of sea otters, thousands of stranded, emaciated, sea lion pups, malnourished salmon, sick halibut, plummeting pollock stocks, and the appearance of some unusual tropical visitors such as sunfish, hammerhead sharks, and even a few venomous, yellow-bellied, sea snakes.


In addition, there was a bloom of the domoic-acid-toxin-producing diatom, Pseudo-nitzschia, which spanned nearly the entire west coast for months. This likely played a major role in the deaths of so many marine mammals and birds and also wreaked millions of dollars of economic havoc with the closure of the west coast dungeness crab fishery. It was the ocean’s equivalent of “raining cats and dogs.”


Perhaps what is more concerning is that this may not have been a random occurrence. According to David Hutchins, Ph.D. of University of Southern California (USC), “these large, toxic blooms could become more common in the future as the California coastal regime continues to warm, and carbon dioxide concentrations continue to rise. The 2015 event may have just been a preview of what may be the new normal.”


So, what happened? At the end of 2013, an unusually warm “blob” of water formed in the Gulf of Alaska due to a high-pressure system that refused to budge. The blob grew in size and depth and spread south down the coast, eventually joining with warm water rising north from Mexico. At its peak, the blob covered 3.5 million square miles from Alaska to Mexico, reaching depths of up to 1,300 feet, with areas up to 7 degrees above average temperature, generating the largest toxic diatom bloom on record for the west coast.


We have become familiar with the stories of bleaching coral in the tropics driven by warming, acidic seas, but the effects of warming and acidification on the temperate coastal ocean is not as familiar perhaps until now. Climate models predict rising temperatures in the coastal ocean over the next century; thus, the million-dollar question on everyone’s minds during the chaos of 2013-2015 was whether this is the new norm.


USC Sea Grant funding was put to work to answer that question. David Hutchins, Ph.D. and Feixue Fu, Ph.D. of the USC Marine Environmental Biology Program explored why Pseudo-nitzschia thrived while the rest of the West Coast cooked. Their results have produced three pending publications[1] detailing the effects of rising temperature and carbon dioxide (acidity) on isolated Pseudo-nitzschia cultures, as well as the changes in a natural California diatom community (that included abundant toxic Pseudo-nitzschia) over a range of temperatures and carbon dioxide levels (with particular reference to the elevated temperatures during the “blob” event of 2015.) These experiments demonstrated for the first time that not only does growth rate and toxicity increase for Pseudo-nitzschia with increasing temperature, but also that the relative abundance of Pseudo-nitzschia nearly always increases compared to other co-occurring diatom species when temperatures are elevated.


As Hutchins puts it, “this diatom is more toxic, grows faster, and outcompetes all others at warmer temperatures.” In other words, Pseudo-nitzschia is that guy in the hot tub who just keeps partying harder, while everyone else gets more sluggish and wrinkled.


Pseudo-nitzschia is always out there in the coastal ocean (and probably always has been), but understanding when, how, and why it creates a toxic bloom affecting the entire marine food chain will help the future management of healthy coastal ecosystems.


Hutchins and Fu have plans to continue their research, with the aim of eventually informing predictive models for major toxic bloom events. According to Hutchins, “This could help warn coastal managers and the fishing industry, helping to mitigate the effects of harmful algal blooms like the one in 2015.”


There may be a new normal, as Hutchins says, but certainly the more we understand, the more we can do to make sure that the new normal is still healthy.

[1] Tatters, A.O., Schnetzer, A., Xu, K., Walworth, N.G., Fu, F.-X., Spackeen, J.L., Sipler, R.E., Bertrand, E.M., McQuaid, J.B., Allen, A.E., Bronk, D.A., Gao, K., Sun, J., Caron, D.A., and  Hutchins, D.A.  (in review). Interactive effects of temperature, CO2, and nitrogen source on a coastal California plankton assemblage: I. Diatom community composition and domoic acid production. Marine Ecology Progress Series


Spackeen, J.L., Sipler, R.E., Xu, K., Tatters, A.O., Walworth, N.G., Bertrand, E.M., McQuaid, J.B., Hutchins, D.A., Allen, A.A., and Bronk, D.A. (In review).  Interactive effects of temperature, CO2, and nitrogen source on a coastal California plankton assemblage: II. Microbial uptake of nitrate, urea, and carbon. Marine Ecology Progress Series


Zhi Zhu, Pingping Qu, Feixue Fu, Nancy Tennenbaum, and David A. Hutchins. Warming Increases Toxicity and Competitive Dominance of the Diatom Pseudo-nitzschia spp. in Southern California Waters.  (in preparation for submission to Limnology and Oceanography Letters)


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