Fringing beds and meadows of eelgrass (Zostera marina) provide important habitat functions and services. Eelgrass, a marine plant in the shallow waters of Puget Sound, serves as food source, nursery and shelter for many species. It also filters sediments and nutrients, improving water clarity, and protects shorelines from erosion. Eelgrass is a valuable ecosystem indicator because it is sensitive to stressors such as pollution, sediment inputs and physical damage, and it allows tracking of both gains and losses in area. This Vital Sign tells us about progress toward recovering healthy eelgrass habitat in greater Puget Sound.


Key Vital Sign Messages

  •              Eelgrass and shiner perch
    There are approximately 56,000 acres of eelgrass in greater Puget Sound. Approximately half of all eelgrass grows in small beds that fringe the shoreline. The remainder grows on broad tidal flats. The largest eelgrass beds are found in Padilla, Samish and Skagit Bays.
  • Soundwide eelgrass area has been relatively stable since 2000, as has overall eelgrass area in herring spawn locations during the last forty years. This is reassuring and sets Puget Sound apart from other developed areas where large scale declines are ongoing.
  • Although eelgrass populations appear to be stable soundwide, there is greater variability at smaller spatial scales, with individual sites increasing or decreasing. Declines are more common in certain areas, such as South Puget Sound and the San Juan Islands. Heads of bays and inlets, where water exchange is reduced, are locations of particular concern. Local declines are likely due to a variety of stressors, such as physical damage, local water quality impairments, and eelgrass wasting disease.
  • Loss of eelgrass to diseases such as eelgrass wasting disease can be devastating to major portions of the marine food web. This disease decimated seagrasses on the Atlantic coast of Europe and North America in the 1930s. Eelgrass wasting disease is present in the Salish Sea, and has caused local declines. Eelgrass wasting disease has the potential to become a major stressor under increasing climate change, as the severity of outbreaks has been linked to warmer water temperatures.
  • Eelgrass health is linked to the Marine Water Quality Vital Sign. Excessive input of nutrients and organic matter can lead to algae blooms, and overgrowth by epiphytes and nuisance macroalgae. These organisms shade eelgrass beds, and lower density and the maximum depth to which eelgrass grows.
  • Climate change and ocean acidification pose a threat to nearshore ecosystems in Puget Sound. By consuming carbon dioxide during photosynthesis, eelgrass has a positive influence on local water chemistry, and could play a role in mitigating ocean acidification while providing refuge for a variety of organisms under changing ocean conditions.

Strategies, Actions, and Effectiveness

Other Resources

Contributing Partners

The Washington State Department of Natural Resources Submerged Vegetation Monitoring Program monitors eelgrass throughout Puget Sound. 

Bart Christiaen (DNR). Reviewed by the PSEMP Nearshore workgroup.
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