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Sediment health declining in central Puget Sound

Bellamy Pailthorp photo

Scientists examining the health of Puget Sound have uncovered a new mystery involving the very bottom of the food chain.

A new study from the state Department of Ecology shows toxins in sediments have declined over the past decade. But it also found declining health of the creatures that live in the sediment. 

Kathy Welch stands on the deck of an Ecology research vessel in Elliott Bay, sifting through mud samples they lifted from the depths. Using a hose, she uncovers marine worms and dime-sized clamshells, and a small white U-shaped creature.

“This little guy is a sea cucumber," Welch says. "They burrow in the sediment. And when we find them—this one in particular—we know that this is a little better type habitat.”

Welch is the lead taxonomist, cataloging all the critters they find in buckets of sediment they’ve been strategically collecting for more than two decades now.

They’ve been testing the samples for toxicity, too. They’ve found lower levels of toxins such as lead and mercury. But despite that, she says, in the area between Whidbey Island and the Tacoma Narrows, the marine life in the sediment is in trouble.

“We’re seeing a decrease in the abundance and the diversity, how many different kinds there are,” Welch says.

The trend is now showing up in 28 percent of Central Puget Sound, a four-fold increase compared to ten years earlier. And it’s still a mystery why.

Rob Duff, the manager of the Ecology Department’s environmental assessment programs, says it could be related to conditions in the open ocean, such as increases in temperature or acidity.

“Or perhaps it’s maybe some chemistry that we’re not monitoring. Because there’s thousands and thousands of chemicals in commerce that we use every day. But in this case, the ones that we monitor aren’t telling us that they’re the problem,” Duff says.

He says emerging contaminants might come from items such as prescription drugs and shampoo or flame retardants that get into runoff. 

The Ecology Department says their scientists are continuing to investigate

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to