There is a weapon that is released by algae around the world and concentrated, invisible, in the flesh of shellfish. An amount the size of a poppy seed is enough to kill a grown person.
Every summer, warm waters bathe the west coast of the United States, Canada, and other parts of the world in toxic algae. Particularly frightening are dinoflagellates in the genus Gonyaulax, Alexandrium, Gymnodinium, and Pyrodinium, which secrete saxitoxin, one of the world’s most lethal neurotoxins. Shellfish swallow saxitoxin and concentrate it in their bodies so readily that eating just one saxitoxin-laden mussel can cause paralysis and even death. Despite government warnings, people are poisoned every year by mussels they’ve gathered and eaten—as are birds, whales, and seals. But algae eaters—including shellfish, pufferfish, and freshwater frogs—remain blissfully unaffected.
Scientists say the combination of especially warm ocean temperatures and large amount of agricultural runoff is contributing to the large — and toxic — bloom.
Domoic acid is just one of many biotoxins that accumulate in fish and shellfish. These marine biotoxins kill 900 people and poison 60,000 every year, on top of poisoning wildlife. They also exact an economic cost: When shellfish become toxic, the harvesting bans threaten the $77 million worth of shellfish sales in Washington state alone. Even worse, new research shows that people and wildlife may suffer from a different form of poisoning when they eat shellfish contaminated with domoic acid below the legal limit.
To most of us it comes as a surprise that crabs can be toxic, but we are all familiar with the rule that oysters should not be eaten except in months that contain the letter “R.” The mnemonic is a clever way to remember not to eat wild oysters and other shellfish during summer months, because the warm water fuels blooms of phytoplankton that contain toxins.
Neurotoxic shellfish poisoning (NSP) is caused by consumption of molluscan shellfish contaminated with brevetoxins primarily produced by the dinoflagellate, Karenia brevis. Blooms of K. brevis, called Florida red tide, occur frequently along the Gulf of Mexico. Many shellfish beds in the US (and other nations) are routinely monitored for presence of K. brevis and other brevetoxin-producing organisms.
Rising global temperatures are clearly linked to increasing waterborne food poisoning, particularly from eating raw oysters, along with other nasty infections, a new study shows.
So, in general, there is likely to be more risk of a harmful bloom in summer and, as a rule of thumb, in the past abiding by the old aphorism may have saved you from some unpleasant stomach upsets.
The consumption of shellfish (e.g. mussels, clams) is one of the most common ways for algal toxins to impact human health.