Coral Growth and Reef Framework Persistence of the Florida Reef Tract with Accelerating Ocean Acidification

Derek Manzello, Ph.D.

Reef Framework ResearchThe thermal effects of climate change have been visually apparent as a recent increase in the frequency and severity of mass coral bleaching events. The impacts of OA are much harder to discern given the less visible nature of this threat. OA describes the progressive, global reduction in seawater pH that is currently underway due to the oceanic uptake of increasing atmospheric CO2. OA is expected to reduce coral reef calcification and carbonate cement precipitation while increasing rates of reef erosion. The relative rates of change in these fundamental reef processes will likely be a function of pCO2 (the partial pressure of CO2) in surface seawater, which is directly proportional to pCO2 in the atmosphere.

Reef framework structures, which are the end result of coral calcification, act as natural breakwaters for Florida Key’s residents and their three-dimensional architecture is a main draw for SCUBA divers. Reef structures are vital to reef-associated biodiversity and fisheries, such as economically important fisheries like the spiny lobster, in addition to local tourism-based economies like that of the Florida Keys. The physical integrity of these structures with impending OA will determine their potential to withstand natural physical erosive processes like storm events given the low coral cover on the Florida Reef Tract. There is thus an urgent need to know just how the building (coral growth) and persistence (carbonate cementation, bioerosion) of these reef structures may change with ocean acidification.

The Florida Reef Tract has a natural inshore/offshore gradient, where reef structure and CO2 conditions are vastly different. This gradient is vastly different between the upper, middle and lower FRT due to the greater influence of Florida Bay waters in the middle and lower keys. Preliminary data from the upper keys has shown that the CO2 conditions on the inshore and much healthier patch reefs are significantly more favorable for coral calcification (lower pCO2, higher aragonite saturation). The high rates of photosynthesis associated with seagrass beds in Hawk Channel are hypothesized to create this gradient, which poses the compelling question, will inshore patch reefs be sites of resilience in the face of OA do to CO2 removal by seagrasses? Is this more favorable carbonate chemistry already a factor contributing to the increased resilience on inshore patch reefs?

These questions are being addressed by characterizing and quantifying the differences in the processes of coral reef construction (coral growth, carbonate cementation) and destruction (bioerosion) relative to these natural CO2 gradients with the support from NOAA's Coral Reef Conservation Program (CRCP).