ABSTRACT
CONTENTS Introduction ............................................................................................................................................ 193
Bio-Optical Modeling .................................................................................................................. 194 Plant Physiology........................................................................................................................... 195
Methods.................................................................................................................................................. 196 Calibrating a Bio-Optical Model ................................................................................................. 196 Light-Stress Experiments ............................................................................................................. 197
Results .................................................................................................................................................... 198 Water Quality Monitoring; North River, North Carolina............................................................ 198 Light Stress Experiment............................................................................................................... 200
Discussion .............................................................................................................................................. 203 Water Quality Stress Indicators ................................................................................................... 203 Plant Physiology Indicators ......................................................................................................... 204
Conclusions ............................................................................................................................................ 205 Acknowledgments.................................................................................................................................. 206 References .............................................................................................................................................. 207
Estuaries and coastal waters are highly productive, ecologically and societally valuable ecosystems. They are under increasing stress from both anthropogenic factors, such as nutrient enrichment and sedimentation, and altered frequencies and intensities of natural disturbances arising across many scales, from inputs to a watershed to those wrought by global climate change. Seagrasses are often dominant primary producers that can play a central role in the stability, nursery function, biogeochemical cycling, and trophodynamics of coastal ecosystems and, as such, are important for sustaining a broad spectrum of organisms (Thayer et al., 1984; Hemminga and Duarte, 2000). For example, they stabilize sediments, which are easily resuspended if the plants are lost, resulting in increased and prolonged turbidity that reduces available light reaching the seafloor. For these reasons, seagrasses are widely recognized as “barometers” of estuarine water quality, being perhaps the most parsimonious integrator of estuarine water quality throughout the range of their current and historic distribution (Dennison et al., 1993). Thriving seagrass communities signal a productive, diverse, and biogeochemically and trophically wellcoupled coastal ecosystem (Harlin and Thorne-Miller, 1981; Thayer et al., 1984; Fonseca et al., 1998; Hauxwell et al., 2001). Accordingly, the presence or absence of seagrass is a useful measure of estuarine condition, but reliance on presence/absence as an indicator implicitly requires significant degradation of estuarine water quality (Zimmerman et al., 1991; Short and Wyllie-Echeverria, 1996). By focusing on seagrass decline, we are restricted to detecting conditions when water quality is already so degraded that there is virtually no time for corrective actions. Therefore, early detection of sublethal stress thresholds in seagrass plants is crucial for effective conservation of this resource.
