Predicted changes in seagrass cover and distribution in the face of sea level rise: Implications for bivalve aquaculture in a US West Coast estuary

Authors: Dumbauld, Brett; Graham, Erin; McCoy, Lee; LEWIS, NATHANIEL - Oregon State University

Submitted to: Estuaries and Coasts - Journal of the Estuarine Research Federation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2022
Publication Date: 3/11/2022
Citation: Dumbauld, B.R., Graham, E.R., McCoy, L.M., Lewis, N. 2022. Predicted changes in seagrass cover and distribution in the face of sea level rise: Implications for bivalve aquaculture in a US West Coast estuary. Estuaries and Coasts - Journal of the Estuarine Research Federation. https://doi.org/10.1007/s12237-022-01060-2 .
DOI: https://doi.org/10.1007/s12237-022-01060-2

Interpretive Summary: Sea level rise (SLR) due to global climate change is expected to result in increased water depth that consequently affects the distribution of important habitats in coastal bays and estuaries. Seagrasses represent one of these sensitive habitats because they are directly affected by the amount of light reaching them at depth. In estuaries along the west coast of the United States, seagrasses often co-occur with shellfish aquaculture. Because some aquaculture practices can also negatively influence seagrass, understanding future shifts in seagrass distribution due to sea level rise and other factors including aquaculture have become a concern for both natural resource managers and aquaculturists. In this study, a model is developed to establish relationships between presence of the native seagrass (eelgrass, Zostera marina) and several other variables and then used to predict its distribution in shellfish aquaculture beds located in Willapa Bay, Washington for the years 2030, 2050 and 2100 under conservative and high rates of SLR. The model predicts that eelgrass will increase throughout Willapa Bay for all SLR scenarios and years, resulting in as much as 34% more eelgrass by 2100 and a 40% increase within aquaculture beds. By 2100, Z. marina could increase in as many as 333 of the 458 aquaculture beds examined and the majority of these beds could experience over 50% Z. marina coverage. Such increases would benefit the organisms that utilize this seagrass habitat, but will also result in challenges for managers and the aquaculture industry.

Technical Abstract: Sea level rise (SLR) is changing coastal habitats that support valuable ecological and economic resources. A rise in global mean sea level (GMSL) will lead to changes in water depth in coastal bays and estuaries, affecting the distribution of seagrasses which provide numerous ecosystem services but are declining globally. In estuaries along the west coast of the United States, seagrasses often co-occur with shellfish aquaculture and some aquaculture practices negatively influence seagrass. Understanding this interaction and future shifts in seagrass distribution have therefore become a concern for both natural resource managers and aquaculturists. In this study, a model is developed to establish relationships between seagrass presence and seven predictor variables (bathymetric elevation, salinity, distance to estuary mouth, distance to nearest channel, cumulative wave stress, sediment composition and burrowing shrimp density), and then used to predict the distribution of eelgrass, Zostera marina in aquaculture habitats of Willapa Bay, Washington for the years 2030, 2050 and 2100 under conservative and high rates of SLR. The model predicts Z. marina will increase throughout the intertidal for all SLR scenarios and years, resulting in as much as 34% more eelgrass in Willapa Bay by 2100 and a 40% increase within aquaculture beds. By 2100, Z. marina could increase in as many as 333 of the 458 aquaculture beds examined and the majority of aquaculture beds could experience over 50% Z. marina coverage. Such increases in Z. marina will potentially result in future management challenges for aquaculture operations.