Status and trends for seagrasses in Puget Sound from 2010-2013

A 2015 report from the Washington State Department of Natural Resources summarizes the status and trends for native eelgrass and other seagrasses in Puget Sound from 2010-2013.

Report cover
Report cover

Executive Summary

The Washington State Department of Natural Resources (DNR) manages 2.6 million acres of state-owned aquatic lands for the benefit of current and future citizens of Washington State. DNR’s stewardship responsibilities include protection of native seagrasses such as eelgrass (Zostera marina), an important nearshore habitat in greater Puget Sound. DNR monitors the status and trends of native seagrass abundance and depth distribution throughout greater Puget Sound using underwater videography. Monitoring was initiated in 2000. The monitoring results are used by the Puget Sound Partnership as one of 21 vital signs to track restoration progress (PSP 2014).

Key Findings:

1. Soundwide native seagrass area has been stable over the monitoring record. There is no significant long-term linear trend in soundwide native seagrass area (permutation test, p=0.63). It is possible that small variations in soundwide native seagrass area occurred below the detection limits of the SVMP program, but seagrass in Puget Sound has not experienced a major decline.

2. Current native seagrass conditions have not yet met the Puget Sound Partnership’s target for a 20% increase in area by 2020. Statistical tests show that current soundwide native seagrass area is less than the target defined by the Puget Sound Partnership. It is too early to tell if the trend in seagrass area is on a trajectory to meet the target by 2020. Test results are equivocal on whether current conditions have progressed from the baseline conditions.

3. Most of the 347 individual sites that were analyzed for change were stable throughout the entire monitoring record. Twenty-five sites decreased in native seagrass area, 17 sites increased in native seagrass area, 209 sites experienced no detectable change, and 60 sites did not have seagrass beds present. Thirty-six sites had insufficient data for trend analysis (sampled only 1 year). Many of the sites with long-term decreases in native seagrass area were located near Hood Canal, Southern Puget Sound and the San Juan Islands.

4. Seagrass conditions improved in the recent 2-3 years. Analysis of individual site data in recent years (n=156) shows that there are more sites with increasing (n=25) than decreasing (n=5) native seagrass area between 2010 and 2013. The reason is unknown; it could be a short-term anomaly or part of a longer-term pattern.

5. Native seagrass area increased at two river deltas following major restoration projects: the Skokomish River delta in lower Hood Canal and the Nisqually River delta in southern Puget Sound.


1. Continue to monitor the status and trends in native seagrasses throughout Puget Sound to meet goals defined by DNR and the Puget Sound Partnership. Improve the monitoring program’s ability to detect long-term trends in seagrass area by revising the soundwide site rotation protocol. Continue to evaluate transect placement protocols at sites for potential improvements to status and trends estimates.

2. Provide technical support and data to scientists and managers on the status and trends in native seagrass, and on sites and regions of concern in Puget Sound.

3. Collaborate with other researchers to further assess changes in sites of particular interest, including those listed in the 2014 Puget Sound Eelgrass Recovery Strategy (Goehring et al. in prep). Initial focus will be on sites:
         a. near river deltas in response to restoration;
         b. in lower Hood Canal where recent increases in eelgrass contrast with long-term declines.


Washington State department of Natural Resources. (2015). Puget Sound Submerged Vegetation Monitoring Program 2010-2013 Report. Puget Sound Ecosystem Monitoring Program. 61 pgs.

About the Author: 
The Washington State Department of Natural Resources is a state agency that manages 5.6 million acres of forest, range, agricultural, aquatic, and commercial lands in Washington; The Puget Sound Ecosystem Monitoring Program is an independent monitoring program and Steering Committee that works collaboratively across participating state and federal agencies and other organizations. It evaluates progress towards ecosystem recovery and serves as a foundation to continually improve the scientific basis for management actions in the Puget Sound.