Port Susan closed to shellfish harvest in October because of a harmful algal bloom that was detected by the Stillaguamish Tribe’s routine plankton sampling.

“Until a few days ago, Port Susan was one of the last remaining open areas in the sound,” said Franchesca Perez, Stillaguamish marine and shellfish biologist. “It is now closed due to the risk of paralytic shellfish poisoning.”

After the dinoflagellate Alexandrium catenella was found in a sample from Kayak Point, mussels collected from the area were found to have three times the amount of toxins that could kill a person who consumed one mussel. Notifications were sent out to the public and the bay was closed to harvest.

The Stillaguamish Tribe has been sampling plankton at Kayak Point since 2013 as part of the SoundToxins early warning program.

“If a certain concentration of toxin-producing algae is found in a plankton tow, then the program notifies the Department of Health, which then tests shellfish tissue to determine if the toxin is present,” said Maggie Taylor, Stillaguamish natural resources technician.

Perez and field project coordinator Rick Rogers scraped about 100 mussels from the pier and shipped them overnight to Olympia.

“Within 24 hours of collection, the toxin concentration was determined,” Perez said.

The first mussel sample contained more than 1,600 micrograms of the toxin per gram of tissue. A second sample taken the following week measured about 500 microgram per gram of tissue.

This is the first time the Stillaguamish Tribe’s sampling has discovered a harmful algal bloom.

“Thanks to the tribe’s participation, it was detected early, just as the monitoring is designed to do,” Perez said.

“We have not seen any more of the offending organism, Alexandrium catenella, in our plankton tows,” Taylor said. “Since this is the first time we have observed a high concentration of Alexandrium in Port Susan, it’s difficult to say how long the toxins will persist. Bloom duration is highly variable between Puget Sound sub-basins but typically only lasts a few weeks.”

The factors that cause a toxic bloom are not entirely understood. They have been associated with higher water temperatures, which could mean that rising temperatures due to climate change could lead to greater severity and duration of the events.

The SoundToxins program is managed by the National Oceanic and Atmospheric Administration’s Northwest Science Center, Washington Sea Grant and the Washington Department of Health.