Although environmental requirements of seagrasses have been studied for years, reliable metrics for predicting their response to current or future conditions remains elusive. Eelgrass (Zostera marina L.) populations of the Chesapeake region lie near the southern limit of their range in the Western Atlantic, exposing them to increasing thermal stress as the climate warms. However, CO₂ stimulated photosynthesis may offset some of the negative effects of temperature stress. The combined effects of temperature, CO₂, and light availability controlled by water quality and epiphytes were explored using GrassLight, a bio-optical model that provided a predictive environment for evaluating the interaction of multiple stressors on eelgrass distribution and density across the submarine landscape. Model predictions were validated against in situ measures of spectral diffuse attentuation and eelgrass density and distribution. The model accurately reproduced the submarine light environment from measured water quality parameters and predicted their impacts on eelgrass distribution. It also reproduced the negative effects of thermal stress on eelgrass growing in the Chesapeake region, even in the presence of epiphytes. Thus, improved water quality should facilitate the survival of eelgrass populations in Chesapeake Bay, even in the face of a warming climate. The bio-optical model is now being integrated into a realistic hydrodynamic simulation using ROMS to explore the relevant spatial and temporal scales necessary to accurately inform options regarding the development of a baywide strategy for managing eelgrass and other SAV in the face of a changing climate.

Richard C. Zimmerman is a biological oceanographer with over 30 years experience in experimental plant physiology, primary productivity of coastal ecosystems, aquatic optics and instrument development for ocean observation. He received B.S., M.S. and Ph.D. degrees in Biology from the University of Southern California. Current research interests include the combined impacts of climate change and water quality on submerged aquatic vegetation and estuarine phytoplankton, and the development of compact lidar systems for remotely observing the vertical structure of the surface ocean.

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