Back to the future: The history of acroporid corals at the Flower Garden Banks, Gulf of Mexico, USA

Fossil elkhorn corals, Acropora palmata, were discovered at the Flower Garden Banks (FGB) on the shelf-margin off the Texas coast in 2006. Radiocarbon dating revealed an A. palmata-dominated community aged 10,157–6838 cal BP. The Acropora reefs correspond in time to an interval of warmer-than-present sea-surface temperatures (SSTs) during the Holocene thermal maximum (HTM). The subsequent demise of A. palmata in the middle Holocene was a consequence of the inability of the shallowest reef facies to keep pace with rising sea level following complete submergence of the banks, possibly coupled with decreasing SSTs following the HTM. In 2007, the first fossil staghorn corals, Acropora cervicornis, were discovered at the FGB. Based on radiocarbon dating of these corals to 1027–211 cal BP, it appears that populations of A. cervicornis flourished in deeper waters (~ 25–32 m depth) on the edges of the banks until the peak of the Little Ice Age (LIA) when they died, presumably from cold-water exposure. The recent return of A. palmata to reefs of the FGB associated with increasing sea temperatures appears to be both an echo of the past and a harbinger of the future.