Date of Award
Program or Major
Master of Science
Catherine M Ashcraft
Frederick T Short
Thomas D Lee
Eelgrass (Zostera marina L) provides essential habitat and forage for waterbirds, fish, and other coastal marine species, nutrient and sediment capture which improves water quality, carbon storage, and wave energy buffering which reduces coastal erosion. Changes in its health can indicate other coastal ecosystem changes. Since the 1980s, eelgrass beds have declined in James Bay, Québec. The eelgrass decline coincided with a decrease in the abundance of migratory Brant and Canada geese visiting the coastal eelgrass meadows, which the geese rely on for forage during their spring and fall migrations. Geese are important species to the coastal First Nation Cree communities of Québec and are harvested by the Cree during these migration periods. The decline in eelgrass and geese threatens culturally significant hunting activities of the First Nation Cree communities of Chisasibi, Wemindji, Eastmain, and Waskaganish. Multiple hypotheses exist for the eelgrass decline but no causes have been directly linked to the loss of eelgrass. As part of a larger coastal habitat monitoring program in James Bay focused on investigating the decline of eelgrass and potential threats and stressors, we developed novel eelgrass monitoring methods suited to the large spatial area and subarctic conditions as well as the eelgrass health index, an index for assessing eelgrass health status.
This study assessed video monitoring as a potential methodology for monitoring eelgrass. Video monitoring and conventional observations were conducted side by side in the Great Bay Estuary in Maine and New Hampshire and compared. Observations for three eelgrass parameters, percent cover, shoot density, and plant height, were made during July and August 2019. Validation for each eelgrass parameter using conventional methods demonstrated that video monitoring results were consistent with results from conventional monitoring. Each of the parameters observed using both methods demonstrated a significant positive linear relationship (p < 0.0001) with a moderate to strong goodness of fit. Cover and biomass data collected from this study and previous SeagrassNet monitoring surveys in the region were also used to develop a model to predict eelgrass biomass from percent cover. A simple linear regression using square root transformed biomass was selected as the best model to estimate biomass from cover. Based on the results, the novel video monitoring methodology is found to be a reliable alternative to conventional monitoring methods, which can improve the ability to collect comprehensive data during field monitoring under certain conditions.
The validated video monitoring methods were then applied to assess the current health of James Bay eelgrass beds. Monitoring of eelgrass percent cover, shoot density, plant height, and biomass was conducted from June to September in 2017 and 2018. Eelgrass cover, density, and height were averaged using the geometric mean equation and reference values to calculate the eelgrass health index (EHI)—a novel tool for assessing eelgrass health status. The eelgrass health index was validated using two methods: 1) biomass observations from James Bay and from five long-term SeagrassNet eelgrass monitoring sites in the United States, and 2) a survey of experiential knowledge. We found that ratings from the new EHI are consistent with accepted metrics and can be used across North America, and with further testing, the EHI could potentially be applied to eelgrass beds throughout the northern hemisphere.
We found that eelgrass is impaired throughout eastern James Bay. Contemporary EHI ratings were compared to historic eelgrass data using a model to predict eelgrass cover from biomass. We found that in comparison to EHI ratings calculated from the historic data, contemporary eelgrass health has declined at two sites in northern Chisasibi, Attikuan and Tees Bay and persisted in similar conditions to the historic environment at Kakassituk.
You may view the thesis presentation accompanying slides here:
Anderson, Nicholas, "The Development, Validation, and Application of the Eelgrass Health Index" (2020). Master's Theses and Capstones. 1375.