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Water column nutrient concentrations and autotrophy in oligotrophic ecosystems are sensitive to eutrophication and other long-term environmental changes and disturbances. Disturbance can be defined as an event or process that changes the structure and response of an ecosystem to other environmental drivers. The role disturbance plays in regulating ecosystem functions is challenging because the effect of the disturbance can vary in magnitude, duration, and extent spatially and temporally. We measured changes in total nitrogen (TN), dissolved inorganic nutrient (DIN), total phosphorus (TP), soluble reactive phosphorus (SRP), total organic carbon (TOC), and chlorophyll-a (Chl-a) concentrations throughout the Everglades, Florida Bay, and the Florida Keys. This region has been subjected to a variety of natural and anthropogenic disturbances including tropical storms, fires, eutrophication, and rapid increases in water levels from sea-level rise and freshwater restoration. We hypothesized that the rate of change in water quality would be greatest in the coastal ecotone where disturbance frequencies and marine P concentrations are highest, and in freshwater marshes closest to hydrologic changes from restoration. We applied trend analyses on multi-decadal data (1996–2019) collected from 461 locations distributed from inland freshwater Everglades (ridge and slough) to outer marine reefs along the Florida Keys, USA. Total Organic Carbon decreased throughout the study area and was the only parameter with a systematic trend throughout the study area. All other parameters had spatially heterogeneous patterns in long-term trends. Results indicate more variability across a large spatial and temporal extent associated with changes in biogeochemical indicators and water quality conditions. Chemical and biological changes in oligotrophic ecosystems are important indicators of environmental change, and our regional ridge-to-reef assessment revealed ecosystem-specific responses to both long-term environmental changes and disturbance legacies. 

Although seagrass ecosystems are valued for the services they provide, anthropogenic impacts have led to global declines in seagrass area. South Florida harbors one of the most extensive and iconic seagrass landscapes in the world, but historic seagrass losses appeared to threaten their integrity. The establishment of the Florida Keys National Marine Sanctuary (FKNMS) in 1995 created a benthic community and water quality monitoring network to aid management efforts. With this study, we report on the status and trajectories of benthic communities in South Florida using 25 years of monitoring data. Overall, most of our permanent monitoring sites maintained stable benthic communities over the period of observation. However, for areas that did experience decline, we identified mechanisms for loss of the climax seagrass Thalassia testudinum in the FKNMS with no or only partial recovery over decadal timescales. We observed a shift towards fast-growing Halodule wrightii meadows at anthropogenically nutrient-enriched nearshore sites along the Florida Keys. In addition, we describe almost complete loss of seagrass meadows at some exposed, back-reef sites offshore from the Florida Keys resulting from physical disturbance by major hurricanes. This study demonstrates the utility of long-term monitoring programs for the identification of benthic community trajectories and their putative drivers on the seascape scale, offering valuable lessons for the design of future seagrass monitoring programs.