Dr. Zimmerman is Professor of Ocean, Earth & Atmospheric Sciences at Old Dominion University. His research interests include the ecological physiology of marine photosynthesis, metabolic regulation of carbon and nutrient dynamics in marine ecosystems, radiative transfer and remote sensing of optically shallow waters, ecosystem productivity and numerical modeling. Current projects involve the physiological responses of seagrasses to climate warming and ocean acidification, and subsequent impacts on Blue Carbon sequestration in shallow coastal seas.
Although environmental requirements of submerged aquatic vegetation have been studied for years, reliable metrics for predicting their response to current or future conditions remain elusive. The combined effects of temperature, CO 2 , 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 SAV distribution and density across the submarine landscape of the Chesapeake Bay. Model predictions were validated against in situ measures of spectral diffuse attenuation, SAV density and distribution. The potential for photosynthesis stimulated by ocean acidification to mitigate the effects of high summer temperature, water quality and epiphyte load on SAV populations growing near the southern limit of their distribution were explored. The model accurately reproduced the submarine light environment from measured water quality parameters, and predicted their impacts on SAV distributions throughout the Bay. It also reproduced the negative effects of warm summer temperatures on eelgrass (Zostera marina L.) distribution in the southern Bay, and demonstrated that CO 2 increases projected for the next century should stimulate photosynthesis sufficiently to offset the negative effects of thermal stress, even in the presence of epiphytes. Thus, improved water quality should facilitate the survival of SAV populations in Chesapeake region, even in the face of a warming climate.