Last week I discussed the toxic algae that cause paralytic shellfish poisoning, and this week, my post is about other species of toxic algae, the symptoms they cause and their impacts on humans and animals.
Amnesic Shellfish Poisoning (ASP) is caused by domoic acid, a biotoxin that is produced by the diatom Pseudo-nitzschia. Fish and shellfish, including bivalves and crab, can accumulate domoic acid with no ill effects, but when humans, other mammals, and birds consume the toxic fish and shellfish, they suffer the effects of ASP. As with paralytic shellfish poisoning (PSP), cooking or freezing the toxic organisms does not lessen the toxicity. This past summer, scientists estimated that the largest-ever bloom of Pseudo-Nitzchia occurred, stretching from California to Southeast Alaska and prompting Oregon and Washington to issue emergency closures for their commercial shellfish fisheries. The bloom was not obvious from sea level, but satellite images showed that a large swath of the ocean had been overtaken by the single-celled algae.
Domoic acid can be fatal if consumed in high doses. It is a neurotoxin that inhibits neurochemical process and can cause short-term memory loss and brain damage. Symptoms appear within 24 hours of ingesting the toxic organism, and they include vomiting, nausea, diarrhea, and abdominal cramps. In more severe cases, neurological symptoms such as a headache, dizziness, confusion, disorientation, vision disturbances, loss of short-term memory, motor weakness, seizures, profuse respiratory secretions, hiccups, unstable blood pressure, cardiac arrhythmia, and coma may occur within 48 hours or up to three days.
In 1987, ASP caused the deaths of three people on Prince Edward Island who ate infected mussels. There is no antidote for domoic acid. Of the 107 confirmed cases, there were four deaths and a few cases of permanent short-term memory loss. Since March 2007, the large increase in marine mammal and seabird strandings and deaths off Southern California has been linked to the recent blooms of toxic algae, and most of the dead animals tested positive for domoic acid.
Ciguatera is not something we worry about in Alaska. It is a foodborne illness caused by eating certain tropical and subtropical reef fish. Ciguatoxin has been found in over 400 species of reef fish, and it can also occur in farm-raised salmon. It is caused by several species of dinoflagellates such as Gambierdiscus toxicus that adhere to coral, algae, and seaweed. The toxic dinoflagellates are eaten by herbivorous fish that are in turn eaten by carnivorous fish that may then be eaten by larger carnivorous fish. The toxin is biomagnified as it moves up the food chain, so predators near the top of the food chain are likely to be the most toxic. Like the other toxins we have discussed, ciguatoxin is odorless, tasteless, and cannot be broken down or removed by cooking.
Symptoms of ciguatera in humans include nausea, vomiting, and diarrhea, usually followed by headaches, muscle aches, ataxia, numbness, vertigo, and hallucinations. These neurological symptoms can persist and are sometimes misdiagnosed as multiple sclerosis. Interestingly, some ciguatera toxins can be passed from an infected individual to a healthy individual through sexual intercourse, and diarrhea and facial rashes can occur through breast feeding in an infant whose mother has been poisoned. The symptoms of ciguatera can last from weeks to years, sometimes as long as 20 years. Most people do recover over time, but symptoms often reappear.
Cyanotoxins are produced by bacteria called cyanobacteria (blue-green algae). Cyanobacteria is found in both fresh and salt water, and blooms often form thick mats or scum over the surface of the water. Sometimes the blooms are such a bright green that they look like paint floating on the water. Cyanotoxins include neurotoxins, hepatotoxins, cytotoxins, and endotoxins. The cyanobacteria neurotoxin BMAA can cause neurodegenerative diseases such as ALS, Parkinson’s disease, and Alzheimer’s disease. Cyanotoxins are toxic to animals as well as humans.
I am intrigued by toxic algae, and I am concerned that as our oceans warm and receive more nutrients from man-made runoff, toxic algae blooms will plague not only humans but also fish, birds, and marine mammals. The dinoflagellates, diatoms, and bacteria that produce marine toxins are tiny organisms that we can’t even see, but their impacts are huge.
I promise a less-technical post next week, and please don’t hesitate to leave a comment telling me what you’d like me to write about. Also, if you are interested in true crime, don’t forget to sign up for my Mystery Newsletter. As soon as you sign up, I’ll send you my first newsletter.