Warming oceans are boosting the frequency and persistence of potentially toxic giant algae blooms, new research exploring the phenomenon off the North American west coast has concluded after years of investigation. The blooms regularly result in losses in the millions in the shellfish industry, a problem that is likely to worsen.
The risk comes from a toxin, domoic acid, which is produced by the algae and then taken in by shellfish, particularly clams and crabs. Often deadly for sea mammals, domoic acid is hardly less of a threat to humans. Consumption of affected shellfish can lead to a serious neurological disorder known as Amnesiac Shellfish Poisoning, with symptoms ranging from gastrointestinal pain to seizures, memory loss and even death.
Longer and more frequent blooms of the toxic algae, from Alaska through British Columbia down to California, have been on the rise in recent years. Domoic acid poisoning had not been spotted in sea mammals north of California until 2015 when a sea lion in Washington waters was found to be afflicted. The Climate Examiner reported last year how scientists had subsequently concluded that the phenomenon was indeed spreading northward.
Researchers have suspected that the problem is related to warmer waters, but whether this is a result of climate change had, until now, remained an open question. Lab experiments have hinted at the conditions that reliably boost toxin production, but without producing a scientific consensus on the matter.
Part of the problem has been that domoic acid was identified as a public health threat in 1987, and domoic acid levels have only been monitored along the west coast since 1991. But the pattern of natural waxing and waning of temperatures in the Pacific fluctuates at the scale of years and decades. So it is only now that the domoic acid monitoring records are long enough to investigate the hypothesised link with climate events.
Last week, scientists with the US National Oceanic and Atmospheric Organization (NOAA) and other west coast research institutes confirmed in a paper appearing in the Proceedings of the National Academies of Science that the timing of elevated levels of domoic acid is strongly associated with the warm phases of two recurring climate events: the Pacific Decadal Oscillation (PDO), which is centred over Pacific Northwest waters, and the El Niño Southern Oscillation (ENSO), the latter centred over the equator and popularly referred to as El Niño and La Niña.
The warmer the seas, the more toxic and more widespread the domoic acid events become. The scientists say that it follows then that while the PDO and ENSO events are natural, the link demonstrated suggests that as ocean temperatures rise as a result of global warming, it would be reasonable to expect that there will be a parallel increase in the amount of poisonous shellfish.
The next steps involve adapting to these new conditions. The researchers are exploring methods for predicting when such toxic algal blooms are likely to happen.
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