Modeling Potential Changes in Seagrass Coverage, Biomass and Vulnerability Under Increased Temperature

Increased water temperature from global climate change may exacerbate existing stresses to eelgrass (Zostera marina) meadows throughout the northeastern United States, possibly leading to declines in populations. In this study, we developed a data-driven model to estimate how seagrass distribution and abundance will likely change with expected temperature increases under climate-change scenarios and applied the model to Pleasant Bay, Massachusetts. Long-term seagrass and water quality monitoring data along with satellite temperature data were used to generate the spatial distribution of environmental drivers across the Bay. These data were then used in a 0-D point-model that incorporated both empirical and mechanistic relationships to predict future spatial seagrass distribution and abundance assuming increases of 1.2°C and 1.95°C by the year 2050. The model demonstrated decline in distribution and abundance with increasing temperature alongside estimated 49 to 93% reductions in biomass. There was a complete loss of regions able to sustain seagrass under the highest temperature scenario. Most of the predicted loss occurred along the shallow and deep edges of the meadows effectively squeezing eelgrass into a narrow depth range where both light and temperature conditions remain favorable for eelgrass growth. These results are intended to help inform the development of targeted conservation and management actions to address the region-wide downward trajectory and facilitate recovery.