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Transforming Puget Sound Ecosystems with Oysters, Kelp, and Eelgrass

February 3, 2025

By Samantha Friborg, Environment and Sustainability Intern

Nestled between Pier 91’s cruise ship berth and the rocky outcropping of Elliott Bay Marina lies Smith Cove Park. The Port of Seattle’s 10-acre green space features a jogging path, picnic tables, and an open field, and it looks out over a small cove. Here the Port experimented with a habitat enhancement project with three main components — Olympia oysters, bull kelp, and eelgrass. In the Puget Sound, these are all keystone species, providing food and habitat for numerous fish and wildlife species, including Chinook salmon.

The Port launched the Smith Cove Blue Carbon Project in 2018 to examine the blue carbon potential of aquatic plants and sediment. “Blue carbon” describes carbon captured in ocean and shoreline environments, sequestered as biomasses or organic material used to create energy, and stored in marine sediments, as opposed to the “green carbon” that land-based plants and soil can sequester. Blue carbon processes represent a natural way to combat ocean acidification resulting from increased atmospheric carbon dioxide emissions. However, the extent of sequestration for individual species, particularly bull kelp, remains unknown. Nevertheless, the Smith Cove Blue Carbon Project sought to understand how oysters, bull kelp, and eelgrass could improve habitat and water quality in a highly urbanized environment.

Additionally, the project aimed to improve the habitat for fish and wildlife. Oyster reefs, kelp forests, and eelgrass beds are among the most ecologically productive ecosystems in the Puget Sound, supporting many fish and wildlife species, including the endangered Chinook salmon. These ecosystems also help protect shorelines from coastal erosion. As storms increase in frequency and severity and sea levels rise due to climate change, stabilizing species like eelgrass, kelp, and shellfish beds can store sediment and dissipate energy away from the fragile coast.

Although the goals of the project shifted based on monitoring results, the project has been valuable for the partnerships it has established and for the insights gained about effective monitoring techniques of these foundational species for the greater region. 

Olympia oyster enhancement

Not only are oysters a part of Washington state’s history and culture, but they also filter and clean the surrounding water and provide habitat and food. Oyster reefs can also provide barriers to storms and tides, slowing erosion and protecting estuarine waters.   

Olympia oysters are the only native oyster in Washington state. Although they exist throughout the Puget Sound, Olympia oyster abundance has diminished since around 1850. The state has been engaged in restoration efforts for these oysters since the development of the Washington Department of Fish and Wildlife’s Olympia Oyster Stock Rebuilding Plan in 1998. The Puget Sound Restoration Fund (PSRF) has carried out aspects of this plan throughout the last two and a half decades. 

From 2018 to 2021, the Port, in partnership with PSRF, planted Olympia oyster spat at Smith Cove to create a new oyster reef. Due to minimal survival rate, in 2021, oysters were placed in a slightly deeper and more protected area west of the original placement, which allowed for some natural recruitment. As of 2023, the oyster population had achieved a moderate density but had not yet established a robust population. The Port plans to continue monitoring the Olympia oyster population at Smith Cove to track how the population develops in this area. 

Bull kelp enhancement

Found in coastal waters, 30-to-60-foot bull kelp stems create a golden-brown forest beneath the sea. Bull kelp is biogenically important, contributing to the ecological productivity and biodiversity of coastal ecosystems. It grows quickly, creating forage and refuge habitat for a host of marine life. With a yearly dieback, bull kelp also contributes substantial amounts of biomass to their marine ecosystems, helping with nutrient cycling.

In 2019 and 2020, bull kelp seed was transferred to the site, in partnership with PSRF. To aid with kelp maturation, rock material was added to two sandy, subtidal areas in the cove in early 2019. Although the rock reef was intended as bull kelp habitat, the reef ultimately became populated by diverse macroalgal (seaweed) species; most of the juvenile bull kelp failed to mature into adults. Although it was not the intended outcome, the abundance of algae along the rock reef replaced a nearly bare benthic habitat (along the bottom of the sea) with a thriving macroalgal community. During the Port’s monitoring efforts, there was some indication of bull kelp recruitment in Smith Cove, however, it ultimately did not establish at the Smith Cove site. 

Pivoting to Elliott Bay

Given the lack of expansion in Smith Cove, from 2021-2023, PSRF and the Port pivoted monitoring to bull kelp beds along the greater Seattle shoreline in Elliott Bay. With PSRF, the Port undertook floating bull kelp bulb counts at areas along the waterfront. This pivot was supported by a new research partnership with the Seattle Aquarium. The aim of the monitoring shifted to examine the conditions where bull kelp was thriving to characterize the physical and biological structure of successful kelp beds. Remotely operated vehicles (ROV) were used to collect the data and artificial intelligence aided in image analysis. Data on bull kelp distribution and abundance was collected. During this timeframe, the linear extent of bull kelp increased by 55% and the number of kelp bulbs increased by 147% along Elliott Bay shorelines.

The bull kelp site surveys from this monitoring effort have formed the basis of a habitat suitability model that will inform future bull kelp restoration efforts throughout Elliott Bay. While the bull kelp seeding in Smith Cove itself had mixed success, the project provided opportunity for new partnerships that will help us better understand these coastal systems. Project partners also successfully leveraged funding from a variety of sources to fuel expanded bull kelp research and restoration in the region, establishing a model for future research. 


Next steps

Bull kelp research continues, thanks in part to the momentum from the Smith Cove enhancement partnerships. PSRF is currently installing an instrument to collect a continuous stream of environmental data about bull kelp near Centennial Park. This data will help scientists understand kelp conditions along eastern shores of the central Puget Sound and compare it with data from western shores in the region. Meanwhile, the Seattle Aquarium secured additional grant funding to expand the use of the ROV kelp mapping technique developed during the project. 

Eelgrass enhancement

The final project component at Smith Cove was an eelgrass enhancement area. The eelgrass at Smith Cove is the only bed located on Port property; it is also publicly viewable at low tides! 

Eelgrass makes up one of the most productive habitats in the marine ecosystem, providing refuge and forage habitat, food for a variety of species, fish spawning ground, and shelter to juvenile fish and invertebrates. Eelgrass helps stabilize the substrate, reducing the risk of coastal erosion. Like oysters, eelgrass filter pollution from the water column thereby improving water quality. Eelgrass is also known to successfully sequester carbon. 

In 2022, eelgrass in Smith Cove was surveyed to compare it with a 2018 survey from the start of the project. 

Here’s what we found:

  • Eelgrass density increased in the study area from 29% to 57%. Additionally, there was a noticeable increase in eelgrass coverage outside of the study area, indicating a positive spillover effect
  • The water temperature inside the eelgrass bed was also lower than unvegetated habitat. Temperatures were overall lower inside the bed and less variable during the summer months. This finding is particularly important when considering marine species that buffer against increasing ocean temperature and ocean acidification.

Given the positive outcome of eelgrass monitoring at Smith Cove, the Port plans to continue studying the factors impacting eelgrass biomass.

Project takeaways

Although the outcomes of the Smith Cove enhancement projects were ultimately different from the initial goals, the projects were valuable. Here are the highlights:

  • The Port and partners have a significantly improved understanding of native oyster, macroalgal community, bull kelp, and eelgrass bed dynamics in Smith Cove and the broader Elliott Bay region 
  • The failure of bull kelp to establish at Smith Cove led the Port to partner with PSRF and the Aquarium to collect long-term data that can be used to track changes in bull kelp extent and eelgrass bed expansion moving forward
  • The projects showcased marine restoration efforts to the public given the location of the cove next to a cruise ship berth, marina, and recreational area and the high visibility of our partners. The projects also attracted the attention of the media, helping shine a spotlight on environmental stewardship and generate engagement around the importance of keystone, native species in urban areas

Since the conclusion of these enhancement projects, the Port has continued working with PSRF, the Aquarium, and the Washington Department of Natural Resources to expand research about Puget Sound oysters, kelp, and eelgrass and support on-going monitoring. 

Smith Cove continues to be an important ecosystem for understanding water quality impacts from nearby industrial activity, ocean acidification, eelgrass and kelp biomass dynamics, and other changes in marine vegetation. The Port will continue monitoring eelgrass and other aspects of the ecosystem at Smith Cove in partnership with the Washington Department of Natural Resources. Seattle Aquarium and Puget Sound Restoration Fund are conducting ongoing bull kelp studies.  

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