Encyclopedia of Puget Sound

Salish Sea snapshots: Detecting harmful algal blooms

Environmental samplers may provide early detection of harmful algal blooms (HABs) in Puget Sound. This toxic algae is expected to increase as the climate changes, bringing with it new and potentially more severe outbreaks of shellfish poisonings. 

Monitoring devices deployed by NOAA for detecting harmful algal blooms. Photo by Rachael Mueller.
Monitoring devices deployed by NOAA for detecting harmful algal blooms. Photo by Rachael Mueller.

Diuretic shellfish poisoning (DSP) officially arrived in Puget Sound in 2011 in the form of a bucketful of gorgeous blue mussels. A vacationing family of four harvested the mussels, but soon after dinner the nausea kicked in, accompanied by diarrhea, vomiting and abdominal pain. It was more than just a nightmare camping trip. It marked a new chapter for harmful algal blooms (HABs), and the illnesses they cause.

DSP is just one of several types of poisoning caused by the ingestion of shellfish that contain toxic algae, and it is a relative late-comer to our waters. Both paralytic shellfish poisoning (PSP) and amnesiac shellfish poisoining (ASP) have been here since 1978 and 1990, respectively. [Read more about toxic algal blooms and shellfish poisoning in the Encyclopedia's Puget Sound Science Review.

As their names suggest, ASP and PSP can be especially severe. Symptoms of ASP can include permanent short-term memory loss and brain damage, while PSP can cause numbness and loss of control of arms and legs and difficulty breathing. Both can be fatal. In all, there are seven types of HABs that occur in the waters of the Salish Sea. 

Unlike other food-born illnesses, toxic algae can’t be cooked or frozen out of food.  The only way to prevent shellfish poisoning from this algae is to avoid consuming the mussels, oysters, clams and scallops that carry it. Now, new technology is being developed to forewarn and prevent contamination. Scientists at NOAA's Northwest Fisheries Science Center have developed a monitoring device that is able to identify toxins in water and send a message warning of toxic algae within three hours of detection. Dr. Stephanie Moore of NOAA described this new technology, known as the Environmental Sample Processor, at the 2016 Salish Sea Ecosystem Conference in Vancouver in April. So far, there are two of the sampling devices deployed on moorings, one in Lummi Bay and another in Samish Bay, with a new one to be installed on a mooring just north of Seattle. These instruments will provide real-time information to industry and recreational harvesters regarding HABs and the potential for toxic shellfish.

Detection of HABs may become increasingly important as the climate changes. HABs and their toxicity levels are expected to increase under warmer and more acidic seawater. That has upset the pre-1970s balance between the HABs and the HAB-nots. Scientists say we can expect to see more and increasingly severe HABs in the future, and possibly more incidences of HAB-related poisonings.  

For now, scientists say, the best bets for consumers are new early detection tools and increased awareness. Health Department officials recommend checking the Washington State Department of Health website on the status of beach closures before harvesting shellfish.