In 1799 about a hundred Aleut hunters working for a Russian-American trading group died in Alaska’s Peril Strait only two hours after eating black mussels collected there. Those who survived did so because they threw up after desperately consuming gunpowder, tobacco and alcohol to purge toxin from their bodies. This was the first recorded incidence of paralytic shellfish poisoning on the west coast of North America.
The Aleuts were killed by natural poisons known as toxins produced by certain algae that were trapped in the mussels’ food-gathering filters. Filter feeders like shellfish, some finned fish and other animals concentrate the toxins present in these algae.
Physical and chemical conditions cause populations of algae to wax and wane in cycles. Out of the vast diversity of plankton in the oceans, the worst offenders are a few species of diatoms, dinoflagellates and cyanobacteria, collectively called harmful algae. For example, some diatoms make domoic acid, which causes vomiting, cramping, headache and even seizures and memory loss; some dinoflagellates produce saxitoxin, which causes numbness, staggering and respiratory failure, among other symptoms.
Toxic blooms can occur naturally when deep, nutrient-rich water wells up in places like the west coasts of North and South America. They can be amplified by land runoff of fertilizers and other chemicals that provide nutrients such as phosphorus. Algal blooms have been increasing in coastal waters nearly everywhere.
In mid-December 2012 recreational mussel harvesting was closed along the entire Oregon coast because the mussels were contaminated with paralytic shellfish toxins. In 2002 razor clam harvesting was prohibited for the full season in Washington State because of high domoic acid levels. Florida’s coastline has frequent outbreaks of the toxic dinoflagellate Karenia brevis, whose toxins can escape into the air and cause severe respiratory distress. Today in the U.S. alone such incidents cause $82 million in public health costs and economic damages to fisheries and tourism annually, according to the National Oceanic and Atmospheric Administration (NOAA). These costs include emergency room visits and other medical treatment, lost work productivity, and fewer dollars reaching local businesses if beaches and sport or commercial fishing is curtailed.
Now scientists are investigating whether climate change could contribute to toxic blooms. As atmospheric carbon dioxide increases, the greenhouse gas is absorbed into ocean water, making it more acidic. The most obvious peril is that marine organisms like clams and sea snails either can’t build their calcium carbonate shells or find their housing harder to maintain. Acidifying ocean conditions could cause toxic algae to become nastier and more abundant. Conversely, the organisms might simply adapt without becoming more poisonous; their numbers could even be reduced.
Of course, researchers must assess ocean acidification as one of many simultaneous stressors in the oceanic environment. Scientists don’t fully understand the relationship between growth rates, toxin production and ocean conditions for these algae. Some species are known to ramp-up toxin production as a defense against predators, others in response to low supplies of crucial nutrients. Another possibility is that the toxins are simply a way for a diatom or dinoflagellate to store excess nutrients, such as carbon or nitrogen, rather than a stress response, says microbial ecologist William Cochlan of San Francisco State University.
To see how nutrient limitation and acidification interact, Avery Tatters, a graduate student in David Hutchins’s lab at the University of Southern California, cultured the diatom Pseudo-nitzschia fraudulenta taken from southern California waters, where it blooms frequently. The species produces domoic acid.