THE GEOLOGICAL INTEGRITY OF FLORIDA’S CORAL REEFS

Contemporary degradation of coral-reef ecosystems has reached a tipping point: continued loss of coral cover, shifts in the composition of reef assemblages away from framework-building taxa, and accelerating reef erosion now threaten both the ecological function of reef ecosystems and the geological process of reef accretion. Understanding how climate change and other anthropogenic disturbances will influence reef building in the future is critical to ensuring the continued construction and maintenance of reef framework and the valuable ecosystem services that reef building supports. Geological records, particularly those from sensitive, marginal reef environments such as the subtropical reef system of south Florida, are key to projecting how the processes of reef-framework construction and destruction will change in the future.

Using an extensive archive of sub-fossil corals collected throughout the 500-km extent of the Florida reef tract, we evaluated the past, present, and a possible future of coral-reef accretion in south Florida. We found that during the early Holocene, rapidly accreting reefs occurred throughout the region. Reef development in south Florida reached its peak during the mid-Holocene climatic optimum but declined dramatically as the climate cooled and more frequent cold fronts impacted south Florida during the late Holocene. By 6000 years ago, the reef tract had contracted to the lowest latitudes of south Florida. By 3000 years ago, reef building was negligible throughout the region.

The shutdown of reef building by 3000 years ago left Florida’s reefs at an unstable equilibrium, wherein a veneer of living coral was the only barrier to reef erosion. Modern climate change and other anthropogenic disturbances have now pushed many reefs into a novel state characterized by the unprecedented loss of reef-building corals and relative increases in non-reef-building taxa, effectively removing that protective barrier and permitting rapid reef-framework erosion. Although the present state of Florida’s reefs is dire, we show that there is still hope for coral restoration to reverse long-term declines in reef accretion on a local scale, until the global-scale threats to coral-reef persistence can be addressed.