Abstract Summary
The Elkhorn coral, Acropora palmata, was the primary reef builder in the western Atlantic over the last 2 million years, however, because of recent region-wide declines this species is now threatened and has prompted conservation/restoration specialists to take new actions. Despite its historical abundance throughout the western Atlantic, A. palmata was only sporadically observed in one small area of Dry Tortugas National Park (DRTO) and has been reported as absent from fossil reef deposits at DRTO. A better understanding of the history of A. palmata at DRTO could provide critical insights into the environmental controls on its growth and decline. Using diver surveys and radiometric dating, we present the first record of late Holocene-aged (~4,500–2,750 years ago) A. palmata populations from DRTO. Contrary to reports from previous studies, however, we show that A. palmata populations in DRTO created extensive reef crest habitats during the late Holocene that may have existed continuously for ~1,750 years. The beginning of this timeframe corresponds to a period of warmer temperatures compared to the later Holocene, and the termination of A. palmata by 2,750 years ago is coincident with overall declines in reef-building at DRTO. If cold water was limiting A. palmata at DRTO in the recent past, that limitation could be lifted now with continued ocean warming. Given that DRTO possesses some of the healthiest modern reefs throughout the Florida reef tract, and its isolation from mainland Florida and other direct anthropogenic impacts, we suggest this as an optimal target area for A. palmata restoration, especially since modern populations there are so limited.
