Mapping changes in Acropora coral species in the upper Florida Keys reef tract

The Florida Keys reef tract is the only reef tract in the continental United States, and the third largest barrier reef in the world. Over 2,800 nautical miles of coastal waters are protected through the Florida Keys National Marine Sanctuary; however, this area is impacted by overfishing, anthropogenic nutrient pollution, and climate change. Corals in this reef tract include the critically endangered Acropora cervicornis and Acropora palmata. Twelve reefs in the upper Florida Keys reef tract were mapped and monitored in 2015 and 2018. Using handheld GPS units, snorkelers marked waypoints of Acropora species. These points were compared for spatial distribution, abundances and density, and percent change in density between the two study years. Spread of A. cervicornis densities across reefs decreased between 2015 and 2018, where as A. palmata density spread increased. Acropora colonies displayed high positive clustering at eight of twelve reefs in 2015, and six of twelve reefs in 2015. Densities and percent changes varied at each specific reef location, with no distinguishable pattern. These reef locations experienced direct impact from Hurricane Irma in late 2017, the only large-scale environmental disturbance between these study years. There has also been an increase in Acropora outplanting effort through time, with seven of twelve study sites having outplants marked in 2018. The continued mapping of coral reef sites in the future can further indicate trends in Acropora population changes in response to multiple environmental stressors over time, which is evidently critical for coral reef research and conservation