Basics
Protected and Restored Habitat
Eelgrass
Indicator
Sound-wide eelgrass area
Vital Sign Indicator
Acre (acres)
/

20 percent increase in the area of native seagrasses (eelgrass and surfgrass) in greater Puget Sound relative to the 2000-2008 baseline by the year 2020.

Bart Christiaen
Contributing Partners
Last Updated
11/17/2020 9:20:22 AM
Map
Size of eelgrass beds (hectares) across five regions in greater Puget Sound. Regions are: Northern Puget Sound (NPS), Saratoga Whidbey Basin (SWH), Central Puget Sound (CPS), Hood Canal (HDC), and the San Juan Islands and the Strait of Juan de Fuca (SJS).
Description
Soundwide eelgrass area is a metric for the overall health of native seagrass beds in greater Puget Sound. Seagrass is an important component of nearshore habitats, and is sensitive to human disturbance. Seagrass responds to changes in water quality, and can be used as indicator of eutrophication.
Vital Sign Indicator Chart
Long-term trend in soundwide eelgrass area (acres) in greater Puget Sound. The dark grey bar represents the 2000-2008 baseline, light grey bars are annual estimates of soundwide eelgrass area, and the dashed line shows the recovery target of a 20% increase in eelgrass area relative to the 2000-2008 baseline by 2020. Error bars are standard error.

Eelgrass and other seagrass species play a key role in the nearshore ecosystem. They provide food, shelter and nursery habitat for a wide range of organisms, ranging from small invertebrates to commercially important fish species and wading birds. Eelgrass also helps prevent erosion and maintain shoreline stability by anchoring seafloor sediment with its spreading roots and rhizomes.

Key Vital Sign Indicator Results
  • The current best estimate of eelgrass area in greater Puget Sound is approximately 56,000 acres (rolling average 2017-2019).
  • Soundwide eelgrass area was relatively stable between 2000 and 2019. The relative stability is reassuring and sets Puget Sound apart from many other developed areas, where substantial system-wide declines are ongoing.
  • While the majority of sites appear stable, the spatial pattern in site level trends suggests that eelgrass is more susceptible to declines in certain areas of greater Puget Sound. Declines are mostly centered in South Central Puget Sound and near the San Juan Islands. Eelgrass seems particularly vulnerable at the end of inlets or in protected embayments.
  • Likely drivers for local declines include water quality impairments, eelgrass wasting disease, high abundance of green macro-algae, and changes in river flow patterns across deltaic flats.
  • At this point in time, it seems unlikely that the recovery target of 20% increase in eelgrass area by 2020 will be met. Stressors that affect eelgrass in Puget Sound will likely need to be reduced to see significant soundwide gains in eelgrass area, depth distribution and overall health.
Methods
Monitoring Program

Washington State Department of Natural Resources Submerged Vegetation Monitoring Program, nearshore habitat and eelgrass monitoring

Data Source

Washington State Department of Natural Resources Submerged Vegetation Monitoring Program, Eelgrass GIS data

The Washington Department of Natural Resources (DNR) monitors status and trends of native seagrass species (Zostera marina and Phyllospadix spp.) in greater Puget Sound through the Submerged Vegetation Monitoring Program (SVMP). This program uses towed underwater videography to generate estimates of eelgrass area and depth distribution. Observations of the nonnative seagrass Zostera japonica are recorded as part of monitoring, but are not included in the estimates.

Between 2000 and 2019, DNR has sampled on average 126 sites per year. At each site, continuous underwater video is recorded along several line transects, oriented perpendicular to shore, using a modification of the methods of Norris et al. (1997). Field sampling is generally conducted from May to September. Soundwide eelgrass area is estimated from a stratified random sample of sites in greater Puget Sound. Annual estimates of soundwide eelgrass area are compared to a 2000-2008 baseline estimate in order to evaluate indicator progress.

For more information on methods, see the latest iteration of DNR's Submerged Vegetation Monitoring Report.

Critical Definitions

Seagrasses in greater Puget Sound include eelgrass (Zostera marina) and surfgrass (Phyllospadix spp.). Eelgrass is by far the most abundant native seagrass. It grows on sandy and muddy substrates between 1.4 meters and -12.5 meters relative to the low tide line (MLLW). Surfgrass is mostly found on hard substrate and along the exposed rocky coasts of the San Juan Islands and the Strait of Juan de Fuca.

Interpretation of Results

DISTRIBUTION OF EELGRASS AND SURFGRASS IN GREATER PUGET SOUND

There are two genera of native seagrass in greater Puget Sound: eelgrass (Zostera marina) and surfgrass (Phyllospadix spp.). Eelgrass is by far the most abundant native seagrass. It grows on sandy and muddy substrates between 1.4 meters and -12.5 meters relative to the low tide line (MLLW). Eelgrass is widespread in Puget Sound, but does not occur in the extreme reaches of southern Puget Sound and Liberty Bay, and is relatively sparse in Sinclair Inlet, Dyes Inlet, and Bellingham Bay. Surfgrass is mostly found on hard substrate and along the exposed rocky coasts of the San Juan Islands and the Strait of Juan de Fuca.

Eelgrass distribution patterns vary across greater Puget Sound. The largest eelgrass beds grow on tidal flats such as Samish Bay, Padilla Bay and Skagit Bay. Half of all eelgrass grows in a large number of small fringing beds spread throughout the Sound (map above). While eelgrass has been observed as shallow as 1.4 m and as deep as -12.5 meters, the majority occurs between 0 and -4 meters relative to MLLW. There is a large scale spatial pattern in seagrass depth distribution in greater Puget Sound. Eelgrass tends to grow deepest near the Strait of Juan de Fuca, San Juan Islands, and the northern portion of Central Puget Sound. It does not grow as deep in South Central Puget Sound, the Saratoga Whidbey Basin and bays and inlets with lower flushing.

TRENDS BETWEEN 2000 AND 2019

Based on data collected by DNR between 2017 and 2019, Puget Sound supports approximately 56,000 acres of eelgrass. Sound-wide eelgrass area has not increased relative to the 2000-2008 baseline and there was not a significant trend in eelgrass area between 2009 and 2019. When looking at change on a site by site basis, patterns vary. Between 2000 and 2019, a total of 794 sites were sampled as part of the monitoring effort led by DNR. Eelgrass or surfgrass was present at 649 sites. Of these sites, eelgrass area increased at 37 sites, declined at 42 sites, and showed no trend at 219 sites. For 320 sites there was not enough data to reliably assess trends between 2000 and 2019, at 18 sites there were only trace amounts of eelgrass or surfgrass present, and 13 sites were obstructed at the time of sampling (map below). Sites with declines were mostly clustered near the San Juan Islands, lower Hood Canal, South Central Puget Sound, and at locations with reduced flushing, such as the ends of Carr and Case Inlet, Westcott Bay, the southern end of Fidalgo Bay and Quartermaster Harbor. Sites with increases were mostly located in the Saratoga-Whidbey Basin and Hood Canal.

Change in eelgrass area at Puget Sound sites across five regions between 2000 and 2019. Regions are: Northern Puget Sound (NPS), Saratoga Whidbey Basin (SWH), Central Puget Sound (CPS), Hood Canal (HDC), and the San Juan Islands and the Strait of Juan de Fuca (SJS).

 

LONG-TERM TRENDS IN SELECT AREAS IN PUGET SOUND

A recent analysis of data from Washington State Department of Fish and Wildlife (WDFW) herring spawn surveys found that eelgrass in Puget Sound has not experienced major declines at herring spawning areas over the past 40 years (Shelton et al. 2016). This is good news and sets Puget Sound apart from many other developed areas where catastrophic declines have occurred.

Out of the 14 herring spawn areas surveyed, eelgrass bed extent increased in 3 areas, decreased in 5 areas and did not change in 6 areas between 1970 and 2012. At local scales, several sites with long-term declines were detected. This pattern of local declines agrees with monitoring results from DNR. Heads of bays seem particularly vulnerable; significant long-term declines have been detected in Quartermaster Harbor, Port Gamble Bay, Westcott Bay and Garrison Bay.

Data on eelgrass abundance in Puget Sound pre-1970 are limited, but there is evidence for declines at several locations throughout the Sound (Thom and Hallum, 1990). The extensive development of Puget Sound pre-1970 is thought to have led to widespread loss of eelgrass in Puget Sound (Shelton et al. 2016).

FUTURE PROSPECTS FOR EELGRASS IN PUGET SOUND

Over the last 40 years, a wide range of environmental legislation has improved and protected water quality and nearshore ecosystems in Puget Sound. Examples are the Clean water Act (1972), which gave the US Environmental Protection Agency the authority to regulate waste water discharge in waters of the United States, the Washington State Shoreline Management Act (1972), which is aimed at protecting the shoreline and its natural resources, and the designation of eelgrass as a habitat of special concern by WDFW. The fact that eelgrass beds in the herring spawn areas of Puget Sound have endured since the 1970’s, despite the large increases in population, suggests that these efforts have paid off. However, the long-term declines in approximately one third of the herring spawn areas, and in many localized areas throughout the Sound, are a reason for concern. Continued management efforts will be critical to avoid large declines and to restore the areas with documented losses in Puget Sound.

In order to ensure the protection of eelgrass, the Puget Sound Partnership set a management goal of a 20 percent increase in eelgrass area relative to the 2000-2008 baseline by 2020. This target was selected based on gains achieved in other regions in response to protection and restoration actions. The Puget Sound Partnership and the DNR developed an Eelgrass Recovery Target Strategy in 2015, to identify pathways towards reaching the management goal by 2020.

At this point in time, it seems unlikely that the indicator goal of 20 percent increase in eelgrass area by 2020 will be met. Stressors that affect seagrass in Puget Sound will likely need to be reduced to see significant soundwide gains in eelgrass area, depth distribution and overall health.

EELGRASS DATA VIEWER

The Department of Natural Resources has made it easy to look up where eelgrass grows in Puget Sound through an online data viewer that contains all data collected between 2000 and 2017.

INTERIM TARGET

Link to interim targets

REFERENCES

Christiaen B, Ferrier L, Dowty P, Gaeckle J, Berry H (2019). Puget Sound Seagrass Monitoring Report – Monitoring year 2016-2017. Nearshore Habitat Program, Washington Department of Natural Resources, Olympia, WA. link

Norris JG, Wyllie-Echeverria S, Mumford T, Bailey A, Turner T (1997). Estimating basal area coverage of subtidal seagrass beds using underwater videography. Aquatic Botany 58:269-287.

Shelton A.O., Francis T.B., Feist B.E., Williams G.D., Linquist A., Levin P.S. (2016). Forty years of seagrass population stability and resilience in an urbanizing estuary. Journal of Ecology. doi:10.1111/1365-2745.12682

Thom, R. M. and L. Hallum (1990). Long-term changes in the areal extent of tidal marshes, eelgrass meadows and kelp forests of Puget Sound, Wetland Ecosystem Team, Fisheries Research Institute, School of Fisheries WH-10, University of Washington.

Eelgrass beds are impacted by changes in water quality, eelgrass wasting disease, physical damage (dredging/anchoring/aquaculture), long-term trends in temperature and precipitation, and changes in the geomorphology of tidal flats. Eelgrass beds experience different stressors depending on where they grow in Puget Sound.

The Puget Sound Eelgrass Recovery Target Strategy is organized by five goals:

  1. Conserve existing eelgrass habitats;
  2. Reduce environmental stressors to support natural expansion;
  3. Restore and enhance degraded or declining eelgrass beds;
  4. Identify eelgrass research priorities; and
  5. Expand outreach and education.

Development of the Marine Water Quality Implementation Strategy began in early 2018 and as of early 2020, work is underway to find agreement about selecting priority strategies that will inform future funding decisions and help set regional priorities for the 2022 Action Agenda. 

Other strategies designed to benefit this indicator include DNR eelgrass restoration efforts and the Washington State Department of Ecology Nutrient Forum which collaborates with Puget Sound communities and stakeholders to find solutions for reducing human sources of nutrients. 

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Reporting Guidance
Reporting Instructions

Not applicable to Vital Sign indicators

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