Field assessments of novel benthic communities emerging with changing coastal water quality in the Florida Keys and the surviving coral species.

Water quality parameters such as temperature, salinity, Dissolved oxygen (DO), pH and nutrient concentration have profound impacts on marine benthic community composition. Past research has focused on the balance between photosynthetic benthic organisms and non-photosynthetic animals that can shift in dominance with responses to changing water quality; such changes in benthic communities are termed “phase shifts”. Yet water quality impacts on benthos are a commonly debated topic in the management of land-based sources of pollution. We address two questions to understand water quality impacts on nearshore benthic communities in the Florida Keys (USA). First, do dredged residential canals serve as point sources of pollution to adjacent benthic communities? Secondly, are the increased nutrient concentrations shifting the dominant benthic organisms in the nearshore benthic communities? We examined 8 study sites in the Florida Keys that included developed residential canals and undeveloped protected shorelines. For each site, a 500m length by 200m width grid was used to randomly sample both the water quality and the benthos quarterly. Within each site, water quality components included temperature, salinity, DO, pH, NOx, TP, TPN, and Chl-a. The corresponding benthic communities were evaluated for both Submerged Aquatic Vegetation (SAV) and invertebrate diversity using the Braun-Blanquet and the point intercept method correspondingly. The hypothesis was that decreased nutrient concentration values would be found with increased distance from the canals. Concurrently, poor water quality decreases the corresponding species diversity. Areas that historically supported coral-sponge-octocoral communities are shifting to SAV dominated benthos with lower species diversity. Special attention was paid to coral species occurring in nearshore communities, with efforts to understand how coral species acclimate to more extreme (than normal) conditions within marginal shallow habitats. The coral “survivors” in polluted nearshore areas could provide insights of how corals will respond to future environmental change.