SEQUIM — A biotoxin that baffles biologists and health officials has once again closed Sequim Bay, the only body of saltwater in Washington state and the U.S. where diarrhetic shellfish poisoning has been found.

Frank Cox, marine biotoxin coordinator with the state Department of Health, said the Tuesday DSP closure bans the recreational harvest of all shellfish in the bay and does not affect commercial operations.

Discovery Bay, further east in Jefferson County and where state health officials also are monitoring levels of DSP, is not affected by DSP.

However, the county’s recreational shellfish harvest beaches are under a seasonal closure with other North Olympic Peninsula beaches.

That closure is because of elevated levels to paralytic shellfish poisoning.

Closures include the harvest of clams, including geoducks, oysters, mussels and other invertebrates such as the moon snails.

All areas of Clallam County are closed for the sport harvest of scallops.

The closures do not apply to shrimp.

State health officials on Aug. 11 reported that three King County residents who ate mussels they harvested at Sequim Bay State Park in late June fell ill with DSP.

Diarrhetic shellfish poisoning can cause diarrhea, nausea, vomiting, abdominal cramps and chills.

DSP causes severe illness while PSP, commonly called “red tide,” can be deadly.

Federal Drug Administration testing of tissue samples taken from mussels in Sequim Bay recently showed elevated levels of DSP, about a microgram above the threshold of 16 micrograms per 100 grams of shellfish tissue.

Cox said the cause of the latest Sequim Bay DSP bloom is still unkown but monitoring will continue.

“We have no idea, but maybe new tests will help us,” Cox said.

It is the second closure of Sequim Bay since it was reopened in mid-October when mussel tissue samples showed declining levels of DSP.

The original DSP-related ban on both recreational and commercial harvesting of all types of shellfish in Sequim Bay began in early August.

DSP comes from a toxin produced by a type of plankton long known to live in high concentrations in Sequim Bay and around Puget Sound, Cox said.

DSP comes from a toxin produced by a type of plankton long known to live in high concentrations in Sequim Bay and around Puget Sound.

Food contaminated with DSP biotoxin may not look or smell spoiled.

DSP can cause diarrhea, nausea, vomiting, abdominal cramps and chills.

As many as 60 cases of DSP have been reported in Canada, believed to be linked to an island at the north end of the Strait of Georgia in British Columbia.

Cases of DSP have also been reported in Europe.

Until it was found in Sequim Bay, the biotoxin had not been discovered in the United States.

For more information, phone the Marine Biotoxin Hotline at 800-562-5632 or visit the state website at http://tinyurl.com/4xmftw7.

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Sequim-Dungeness Valley Editor Jeff Chew can be reached at 360-681-2391 or at jeff.chew@peninsuladailynews.com.