Abstract
The waters of the Florida Keys are naturally oligotrophic, however, discharge from the Everglades, anthropogenic changes to the coastline, and groundwater runoff from the carbonate islands contribute excess nutrients to the ecosystem. Eutrophication is acknowledged as a major threat to coastal ecosystems and successful efforts have been made to reduce direct anthropogenic nutrient pollution. The main driver of eutrophication is nutrient input; this study focuses on the nitrogen and phosphorous content of the water column. Eutrophication is also driven by hydrologic exchange, as the main method of transport of anthropogenic nutrients into the system is groundwater runoff. Chemical responses in the water column are indicated by reductions in dissolved oxygen saturation and pH. Benthic response to eutrophication is measured in this study by quantification of submerged aquatic vegetation (SAV) using Braun-Blanquet cover abundance (BBCA) surveys.Gaussian mixed modeling identifies two clusters of points based on water quality characteristics, reflecting opposing eutrophic states. Linear discriminant analysis is presented as a method by which the multi-dimensional eutrophic state of the water column can be expressed with a single metric.A Thalassia testudinum dominated community, a mixed SAV community, and two macroalgae-dominated communities are recognized. pH is identified as a strong indicator of the eutrophic state of the water column. Seagrasses drive a high variability in dissolved oxygen saturation resultant of variation in light availability. A macroalgal gradient exists that aligns with the degree of eutrophic stress imposed on the water column in the form of dissolved oxygen reduction and acidification with increased stratification of the water column. This gradient is representative of a qualitative succession that is observed across the study areas as a response to, or recovery from, eutrophication.