OLYMPIC COAST-The lethal levels of a biotoxin recorded in Olympic coast California mussels earlier this summer highlighted an emerging trend. Shellfish harvest closures due to the risks of paralytic shellfish poisoning (PSP), historically low on the coast, may become more frequent because of a change in microscopic plants in the ocean.
As a participant in the Olympic Region Harmful Algal Bloom (ORHAB) partnership, Quinault Indian Nation (QIN) collects and analyzes seawater samples for the types of plankton and their levels that can indicate whether a harmful algal bloom is occurring. For many years, the main concern for QIN has been the levels of the plankton species pseudo-nitzschia. It causes the production of the biotoxin domoic acid in shellfish such as razor clams and Dungeness crab.
“Pseudo-nitzschia is a diatom. Diatoms were the dominate type of plankton in the waters off QIN’s coast up until about two years ago,” said Joe Schumacker, marine scientist for Quinault Indian Nation. Now, the balance has shifted to different species of plankton like the PSP-causing Alexandrium catenella.” “It’s a dinoflagellate that used to be a relatively rare presence in our coastal water,” said Schumacker. “But for the first time in modern memory, we had to close razor clam harvest last year because of a large bloom of Alexandrium and resulting PSP levels.”
Dinoflagellates have whip-like tails that allow them to move up and down in the water column and feed, while diatoms such as pseudo-nitzschia simply drift in the water. Alexandrium also thrives in waters that are layered, for example when fresh water and salt water are mixed. Scientists with ORHAB and the University of Washington believe ocean conditions will continue to favor it and other dinoflagellates because they can move to find nutrients.
California mussels are an early warning that PSP biotoxin levels may begin to rise in razor clams, which take longer to show biotoxin levels. “We increase our sampling of mussels and razor clams when we see the California mussels with high levels of the biotoxin,” said Jerry Borchert, of the Office of Shellfish and Water Protection in the Washington State Department of Health.
Eighty micrograms of toxin per hundred grams of tissue is the limit for human health. Mussels sampled June 1 by the Quileute Tribe near Second Beach showed levels as high as 3,601 micrograms per hundred grams of tissue. Makah Tribe samples collected June 7 registered nearly 2,000 micrograms at two beach sites. Prior to this year, the highest recorded level on the coast was 832 in 1997.
“At those higher levels, a person could die after just a couple of bites,” Schumacker said. Hoh, Makah, Quileute and Quinault Indian Nation all harvest mussels as part of their traditional diet.
Early symptoms of PSP are a tingling of the lips and tongue. Tingling can appear within minutes of eating poisonous shellfish or may take an hour or two to develop. Depending on the amount of toxin a person has consumed, symptoms may progress to tingling of fingers and toes and then loss of control of arms and legs. Difficulty breathing follows, and death can occur in minutes. Mussels, cockles, clams, scallops, oysters, crabs and lobsters are all known to cause PSP.
Through the ORHAB partnership, coastal tribes are working to encourage additional research into improving forecasting of HAB events. Tribes are also working with scientists to improve rapid tests for shellfish tissue that would eliminate the current need to wait for results from the Department of Health.
“When we get these high levels of biotoxin in mussels, we’re also concerned about its ability to persist in some of these bays and inlets where sampling may not be occurring,” said Schumacker. “For Quinault, it will be an ongoing health issue as well as a cultural issue when it affects harvest of these important species.”