Mussels Help Keep Watch on Pollution in Puget Sound

The humble bivalves, which concentrate everything from heavy metals to cancer drugs in their tissues, provide an ideal way for scientists to monitor nearshore water health.

Mussel harvesting on the waters of Oyster Bay in the Totten Inlet near Shelton, Washington


 Ted S. Warren/Associated Press

Beyond the Douglas fir and madrone trees above Wing Point’s beach on Bainbridge Island, the skyline of Seattle looms, just eight miles across Puget Sound. But look down into the water and you might spot, among the tidal flats bubbling with clam holes and adorned with anemones, a cage with mussels in it.

It’s part of a nationwide environmental contaminant monitoring project, managed by the National Oceanic and Atmospheric Administration (NOAA), called the Mussel Watch Program. Run mainly in coastal areas, the program has grown significantly since its founding in 1986. From the 145 sites the program began with, Mussel Watch is now active in more than 300 locations across the United States, including the Chesapeake Bay, the Great Lakes, the Gulf of Maine, the Southern California Bight, and in waters off Puerto Rico, Hawaii, and Alaska, as well as in Puget Sound. Each project area brings together local and state government agencies, tribal governments (in the Puget Sound region), and citizen scientists who use the mollusks to monitor water quality in the intertidal zone.

An oyster catcher snacking on mussels at low tide


Marneejill via Flickr

Understanding the chemical inputs to this boundary between land and sea is important for the health of both coastal communities and marine life. In the Puget Sound area, that includes thousands of workers involved in the commercial fisheries industry as well as millions who eat seafood from the region, including the tribal nations and communities whose traditional diets rely on fish and shellfish. (Shellfish has, in fact, become more of a mainstay of western Washington Indian tribal economies in response to the rapid decline of many of the region’s salmon stocks, according to the Northwest Indian Fisheries Commission.) Endangered Southern Resident orcas, sea lions, otters, sea birds, and myriad other animals also call the intertidal home and depend on the waters’ bounty for their own diets.

Understanding what mitigation measures work to reduce the flow of pollutants is also key. Sediments can tell part of the story, mussels another. Why mussels? Unlike fish and marine mammals, these creatures don’t have a liver, so they don’t metabolize the chemicals in the water. Instead, “mussels concentrate the chemicals, and they build up in their tissues until they get to an equilibrium with the local environment,” says Mariko Langness, a biologist with the Washington Department of Fish and Wildlife. “That gives you a really good snapshot of the current contaminants in the water that haven’t been altered and changed by metabolic processes.”

For the Puget Sound arm of Mussel Watch, some 10,000 bivalves are deployed to around 100 sites. A majority are concentrated in waters near the cities of Seattle, Tacoma, and Bellingham; some surround the Navy base in Bremerton; and many more are scattered in the inlets and along the shorelines of the islands of Bainbridge, Whidbey, and Orcas.

All the tested mussels begin at the same place—Whidbey Island’s Penn Cove Shellfish, which otherwise grows oysters, clams, and mussels for local restaurants. Unlike their counterparts bound for the steamer, those donated to Mussel Watch are put in cages and lowered into their designated locations over the course of a single fall week, at night. The task of distributing the mussels to so many sites around Puget Sound is made possible by various community groups and volunteers.

In previous incarnations of the Mussel Watch Program, scientists tested existing mussels in situ, in their natural beds, but these beds could move up and down the beach, shifting their proximity to or from contaminant sources and even disappearing altogether. Now, by using sourced, caged mussels, researchers get better data and can make more accurate year-to-year comparisons. “Cages reduce variability,” says Langness. “We want uniform populations and baselines at each location, so cages give us those advantages.”

After three months in the water, the mussels at all 100 locations are collected and brought to Olympia. There, members of the U.S. Department of Fish and Wildlife, along with volunteers, crack open the mussel shells, working site by site, and scoop the tissues into a giant blenderlike machine. The mixture from each site’s population is frozen, and the resultant “smoothies” are shipped to a lab.

The scientists testing the mussel smoothies are searching for around 20 heavy metals and 150 organic compounds. These include persistent organic pollutants (POPs) like polychlorinated biphenyls (PCBs, once used in hundreds of industrial applications, from plasticizing paint to insulating electrical equipment), polycyclic aromatic hydrocarbons (PAHs, a class of chemicals found in coal, crude oil, and gasoline), polybrominated diphenyl ethers (PBDEs, used as fire retardants in plastics and textiles), and the notorious pesticide DDT. Scientists test for a number of variants of each chemical—most of which are human-caused.

Some of these chemicals have been banned for decades but still persist as legacy chemicals, like PCBs and DDT, both toxic to people and wildlife. Many bind to soil, sediment, and the fatty tissues of animals, meaning they can work their way up the food chain, starting with small invertebrates and eventually accumulating in bigger fish and the birds and people that eat them. (For their part, PCBs cause cancer in animals, and the EPA classifies them as probable human carcinogens; they can also do significant harm to our immune and endocrine systems, affect reproduction, impair neurological development, elevate blood pressure, and cause skin rashes.)

A tagged freshwater mussel that was used in a study on toxic contaminants in the Anacostia River in Washington, D.C.
Credit: Will Parson/Chesapeake Bay Program

Over the last few years, the Mussel Watch Program has also begun testing for about 300 chemicals of emerging concern, or CECs. These are associated with human activities and are contained in personal care products, detergents, pharmaceuticals, new pesticides, and other mostly unregulated contaminants. According to Dennis Apeti, who manages the Mussel Watch Program for NOAA’s National Centers for Coastal Ocean Science, many of these CECs were put in place or manufactured to replace an old contaminant that was banned. “We are seeing them accumulate in the environment, and so they are an emerging concern,” he says.

Researchers examining the Puget Sound mussels have detected antibiotics, SSRI drugs, and cancer drugs (all considered CECs) in about half the tested locations, especially near cities. “Most of these inputs are from wastewater treatment plants—from when you pee or put anything down the drain,” says Langness. “Wastewater treatment plants don’t have the facilities to filter them out; the technology isn’t there or it’s expensive.”

Besides toxins, Mussel Watch looks at other environmental health concerns, like parasites. A 2008 NOAA report noted that the program’s histopathology component tests for nearly 70 diseases and parasites found in mussels and oysters, and that identifying trends in the data could help to assess the effects of global warming. Parasites tend to multiply in warmer waters, though it’s a complex system and researchers are still studying how increases in storm events and water temperatures affect the concentration of parasites in mollusks.

For marine wildlife advocates, the hope is that these data lead to local mitigation efforts. “Puget Sound is designated critical habitat for orcas,” says Giulia Good Stefani, a senior attorney in NRDC’s Oceans division. Southern Resident orcas, designated as being at “high risk of extinction” in 2015 by NOAA and now numbering only about 72 individuals, are increasingly vulnerable to environmental pollutants. As the largest and longest-lived members of the dolphin family (they can live to be 100 or more), and as apex predators, orcas bioaccumulate toxins. NOAA cites endocrine disorders, reproductive dysfunction, a compromised immune system, neurological problems, unusual behavior, and cancer as potential effects of various POPs.

When orcas lose weight, those toxins, which are stored in their fat, are metabolized and released into their bloodstreams. Currently the Southern Resident orcas aren’t getting enough food due to a lack of salmon. That leads to high reproductive mortality rates, says Stefani. “Seventy percent of calves are aborted in the late term, when it’s especially dangerous for a mother to lose her calf. And when mothers nurse calves, they burn through fat stores, to produce milk for the calves. They are then transmitting those toxin loads.” Currently, half of all calves that are born die in their first couple of years.

There’s a lot more for researchers to learn, including the effects of those newer CECs on Puget Sound’s animals. Mussel Watch, of course, is just one way to keep track of these chemicals. “I think Mussel Watch, together with other monitoring programs like direct water testing and sediment testing, is a great addition to the rest of the work. Any of these programs alone isn’t enough to tell the story,” says Mindy Roberts, the Puget Sound director of the Washington Environmental Council. Still, considering what’s at stake—beloved local wildlife, a human food supply, and human health—“there’s just not enough monitoring going on.”

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