Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


Dean E. Wendt, Mark A. Moline


Seagrasses are well known for the important ecological roles they play in coastal marine waters worldwide. However, the severe rate of decline observed in seagrasses this century is expected to accelerate with climate change. Conservation efforts can be improved by quantifying physiological thresholds of seagrasses and using these estimates in modeling to forecast changes in distribution. This study examines the response of eelgrass (Zostera marina L.) across current temperatures to look for early warning signs of vulnerability and to evaluate the ways we determine critical thresholds for survival. Whole eelgrass ramets, collected from three beds in Morro Bay, California, were used to develop photosynthesis-irradiance (P-I) curves from 10-20°C. Productivity was not affected by changes in temperature when traditionally measured as the light-saturated photosynthetic rate to dark respiration rate (P:R) ratio. However, photosynthesis in light-limited conditions declined at higher temperatures, suggesting a decrease in productivity when coupled with the increased respiration rates observed at higher temperatures. Irradiance thresholds increased with temperature; critical irradiance was the most sensitive to increases in temperature due to the inclusion of overnight energy use, which also increases with temperature. Measurements of root and rhizome respiration, overnight respiration, and variation across eelgrass beds reveal that these are important components to consider when calculating survival thresholds to use in modeling. Differences in physiological responses across beds suggest that some eelgrass beds operate more efficiently than others in current conditions and are likely to be more resilient to the progressing stressors of climate change. Management of eelgrass in the face of climate change will require reliable distribution forecasts, and therefore accurate estimates of physiological thresholds, to guide mitigation and restoration efforts.