As the second-largest estuary in the country, Puget Sound in Washington State is an immensely important body of water to those living in the Pacific Northwest. Its nearshore waters and 1,300 miles of coastline provide essential habitat to fish and wildlife, including commercially and culturally important salmon and shellfish.

The Puget Sound area is also home to a population of nearly 3.5 million people that is expected to surpass 6 million by 2050. Decades of growth and development have impacted natural processes in the estuary, threatening the unique habitats and overall health of the Sound. In an effort to understand the function of nearshore habitats and develop approaches to restore them to be resilient into the future, USGS and partners are conducting science at the grassroots level—eelgrass roots, that is.

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“It’s difficult to overestimate the importance of Zostera marina, the common eelgrass,” said Eric Grossman, USGS Research Geologist at PCMSC and lead researcher on the Coastal Habitats in Puget Sound (CHIPS) project. “It’s fast-growing, adaptive, and is the most widespread flowering marine plant in the Northern Hemisphere, growing in estuaries from subtropical to subpolar regions.”

A single acre of eelgrass produces almost ten tons of leaves annually—a rate of productivity rivaling that of tropical rainforests—and these meadows of eelgrass provide essential habitat to a wide range of fish and wildlife.

In Puget Sound, birds and fish, including juvenile salmon and Pacific herring, feed on the diverse assemblage of plants and invertebrates living on the eelgrass, and the meadows provide refuge from predators for juvenile fish.

“Eelgrass beds also serve to buffer wave energy and tidal currents, reduce sediment resuspension, and retain sediment,” said Renee Takesue, USGS Research Geologist at PCMSC who studies the interactions between eelgrass and the environment. “This stabilization of the substrate may help to prevent beach erosion, and nutrients and organic matter retained along with the sediment contribute to the productivity of the nearshore.”

“The U.S. EPA, Puget Sound Partnership and area tribes have agreed that eelgrass is important enough that it is one of the ‘Vital Signs’ and targets for Puget Sound recovery,” said Grossman. “One of the Partnership’s goals was to recover 20% of the region’s eelgrass by 2020, based the average cover between 2000 and 2010. That eelgrass recovery target still has not been met.”

Humans, whether directly or indirectly, impact the extent of eelgrass in Puget Sound. Eelgrass requires cool, clear water to grow; sediments suspended in the water block light, restricting growth. Historic and ongoing land-use activities—namely the modification of stream and shoreline hydrology and sediment dynamics—have changed how sediment is distributed at river deltas and in littoral zones, limiting the abundance of eelgrass and in some cases leading to eelgrass declines.

“With the CHIPS project, we partner with tribes and Washington State Department of Natural Resources, the agency leading eelgrass monitoring and recovery efforts, to evaluate historical and recent patterns of eelgrass distributions, processes affecting eelgrass health, and how eelgrass habitats and fish they support respond to gradients in disturbance,” said Grossman.

PCMSC scientists have assessed change in eelgrass distributions in the Nooksack, Skagit, Stillaguamish, Nisqually and Skokomish river deltas based on comparison of historical imagery and repeat high-resolution acoustic surveys. A unique aspect of the USGS efforts is the continuous spatial coverage of maps that help quantify changes.

The CHIPS project is helping to identify physiographic areas in Puget Sound where eelgrass recovery could be most successful. Grossman and his team are finding that the largest potential gains for eelgrass recovery exists in large river deltas where expansive delta tidal flats and other gradually sloping tidal environments can support thousands of acres of the habitat. The team notes that the quality of the habitat is equally important, and eelgrass recovery should be prioritized in large deltas where estuary habitat loss has created a bottleneck for juvenile salmon.

“If the goal of land- and natural resource managers in Puget Sound is to restore as much eelgrass habitat as possible, our role is to provide people the information they need to make decisions about better land-use practices in the future,” Grossman said.

More recently, the CHIPS team is investigating eelgrass’s ability to trap sediment and how this mechanism might affect the chemical environment in Puget Sound. Persistent environmental contaminants such as PCBs and PAHs adhere to fine sediments and organic matter, which may build up in eelgrass beds and potentially transfer up the food chain through organisms.

Additionally, eelgrass growing in anoxic, or oxygen-poor, sediments may play an important role in sequestering buried organic carbon.

“Eelgrass research is experiencing something of a renaissance right now because ‘blue carbon’ could offset carbon emissions,” said Takesue. Blue carbon is the carbon captured by oceans and coastal ecosystems. Due to its vast extent, eelgrass could play an important role in sequestering organic carbon along coasts. “I spent many years characterizing eelgrass beds and identifying environmental stressors, but now the studies are getting more targeted. We’re making strides toward better understanding the role eelgrass plays in climate resilience in large estuaries like Puget Sound.”