Project Background
Puget Sound is home to five species of seagrass, and several hundred species of macroalgae, including over a dozen species of kelp. These plants and algae serve as critical habitat for a wide variety of organisms, including several fish species that are listed as endangered or threatened under the Federal Endangered Species Act.
Eelgrass (Zostera marina) is by far the most abundant seagrass in greater Puget Sound, growing mostly in the intertidal and shallow subtidal in muddy to sandy substrates and low to moderately high-energy environments.
The term kelp refers to a group of large brown macroalgae in the order Laminariales. These algae are found throughout greater Puget Sound, and are often the dominant vegetation in intertidal and subtidal habitats with solid substrate.
Eelgrass and kelp are both provide incredibly productive habitats and serve important ecosystem functions, including the following:
- Producing large amounts of carbon, which contribute to both local and distant food webs.
- Creating structurally complex habitat to provide refuge for marine species.
- Supporting high biodiversity and serve as important habitats for forage fish and juveniles of salmonids.
Eelgrass and kelp are sensitive to stressors such as climate change, physical disturbance, and eutrophication, and are considered important indicators of habitat condition and ecosystem health. Both eelgrass and kelp are included in the Puget Sound Partnership’s list of Vital Signs for Puget Sound recovery.
Marine Vegetation Monitoring Partnership with DNR
From 2019-2022, Snohomish County Marine Resources Committee has been working with the Washington State Department of Natural Resources (DNR) to conduct a comprehensive study of marine vegetation (eelgrass submerged kelp, and other macroalgae) along the shoreline of Snohomish County.
Eelgrass and other marine vegetation 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.
Seagrasses are used as an indicator of estuary health throughout the world, because of their fast response to changes in water quality. Changes in the abundance or distribution of this resource are likely to reflect changes in environmental conditions. They are also likely to affect many other species that depend on seagrass habitat.
DNR monitors abundance and depth distribution of native seagrasses to determine status and trends in the greater Puget Sound area through the Submerged Vegetation Monitoring Program (SVMP). The SVMP monitors a selection of sites throughout the Puget Sound and extrapolates site-level data to create regional estimates of eelgrass area. Data is collected through submerged videography, based on DNR’s SVMP protocols. By partnering with DNR, Snohomish County was able to get a comprehensive survey of the entire Snohomish County shoreline. The monitoring results are used by DNR for the management of State-Owned Aquatic Lands, by the County and local jurisdictions to understand critical areas on their shoreline, and by the Puget Sound Partnership as one of 25 Vital Signs to track progress in the health and recovery of Puget Sound.
Key findings from the monitoring include the following:
- There was approximately 906 hectares of eelgrass in 1999-2007 and approximately 912 hectares of eelgrass in 2019-2022
- Comparing the 2019-2022 data with the 1999-2007 data it appears that there is little change in overall eelgrass area over time at a countywide scale, but variability at smaller scales was observed. Sites with increases in eelgrass were mostly located in the central and northern part of Snohomish County and are identified in purple on the map. While three sites showed a decrease trend and are identified in orange on the map.
- The depth distribution of marine vegetation in the study area was similar to other sites in the Central Basin of Puget Sound.
The Snohomish County Marine Resources Committee’s goal is the repeat this comprehensive monitoring every 7-10 years.
Additional details on the analysis can be found in the reports linked below.
Links to the Reports
For more information on the 2020 Marine Vegetation Monitoring of the Snohomish Delta, view the full report here: Eelgrass, kelp and other macroalgae near the Snohomish delta - Final report to Snohomish County
For more information on the 2021 Marine Vegetation Monitoring of South Snohomish County, view the full report here: Eelgrass, kelp, and other macroalgae in South Snohomish County - Final report to Snohomish County
For more information on the 2022 Marine Vegetation Monitoring of East Port Susan and Gedney (Hat) Island, view the full report here: Eelgrass, kelp, and other macroalgae in South Snohomish County - Final report to Snohomish County
Download a .zip file of all of the eelgrass mapping data.
