Photo: Robyn Rice
Marine Vegetation Monitoring

Marine Vegetation Monitoring

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. 

Kelp Monitoring Overview

Bull kelp (Nereocystis leuktean) is the largest species of brown algae native to our region. This fast-growing seaweed can grow as much as 60 feet in length in a single year and is an important part of the rocky inter tidal ecosystem. It serves as both a primary producer in the food web of Puget Sound and as shelter and habitat for fish, invertebrates, marine mammals, and birds. In addition, the intricate structure of this living habitat buffers against current and wave energy, to help protect the nearshore ecosystem.

In the Puget Sound, there have been noticeable declines in bull kelp abundance. While it is unclear what has caused these declines, potential factors include toxic pollutants from storm water, erosion, high sedimentation deposition, and overpopulation of kelp predators. 

Project Goals

In response to concerns over bull kelp decline and as part of our nearshore conservation goals, Snohomish County MRC seeks to understand how much kelp habitat is currently available in local waters. Towards that end, all seven regional MRCs throughout the Puget Sound are continuing to gather data as part of the Northwest Straits Commission’s Regional Kelp monitoring project (2016) which contributes to an expanding regional story map and interactive Arc GIS database that tracks changes in number of kelp beds and total acres measured. MRC members recently completed our monitoring via kayak in August 2020.


What the Snohomish MRC is Doing About Kelp

The MRC kayak surveys cover the entire southern portion of the Snohomish County Nearshore from the Snohomish/King County border northward to the Snohomish River Delta. The MRC uses a standard protocol developed by The Northwest Straits Commission to simply and reliably monitor changes in existing kelp beds.

You can download detailed printable maps of kelp beds below:

Kelp monitoring data can also be viewed on the SoundIQ database, the Northwest Straits Commission’s web-based application to share data collected by MRCs and the Commission in an easily-accessible map format. MRC data on SoundIQ can be viewed in combination with complementary data from other sources.

Marine Vegetation Monitoring