by Kimberly Coombs
Coral reefs vary in structural architecture, meaning that the structure can be very complex or relatively simple. The more structurally complex a coral reef is, the more species diversity may be supported. The reef building corals that create the complex coral reef structures need to have a sustainable carbonate budget in order to continue the processes of accretion and erosion to build the coral reefs. These corals have been experiencing reductions in their carbonate budget; as a result, they have declined around the world.
Bozec et al. (2015) developed a mechanistic model that estimated reef topographical complexity under different scenarios for Caribbean reefs. They ran the model in order to investigate how Caribbean coral reefs topographical complexity may be impacted by global warming conditions in addition with hurricanes and management actions related to parrotfish population levels. They also ran the model to make predictions about the future of Caribbean coral reefs under the previously mentioned conditions. The model is able to calculate coral carbonate accretion and erosion on a coral colony scale. The model further simulates possible variations in coral surface and volume and the influence this may have on the topographical complexity.
Bozec et al. found that parrotfish populations may help prevent or lessen some of the negative impacts from global warming and hurricanes. Parrotfish aid in bioerosion on the coral reefs; therefore, keeping parrotfish grazing at relatively high levels will enable coral reefs to recover better from bleaching and hurricane disturbances. They also found that disturbances to the coral cover came more from hurricane disturbances than global warming, which they suggested is due to the strong currents that may lessen or prevent temperature changes occurring at these coral reefs. Bozec et al. believe that corals with strong skeleton structures form Caribbean coral reefs in order to withstand the impacts from hurricanes. Other studies have reported most losses in Caribbean corals due to hurricanes occurred within species that had delicate skeleton structures. Bozec et al. also noted the Caribbean corals reefs’ resilience to global warming and hurricanes is due to the corals’ ability to recover relatively quickly to these disturbances. The corals accretion rate outweighed the erosion of their carbonate budget from such disturbances; therefore, allowing the coral reefs to withstand severe damages. As for future predictions, the authors’ estimate that under current trends, the structure of the coral reefs may decay over the next three decades, while under high hurricane occurrences, the coral reefs may decay in less than twenty years.
There was an assumption the authors made when running their model that may interfere with the credibility of their predictions. They assumed that the dead and live coral skeletons mostly influence the coral reef surface. Thus, the simulation did not take into account the carbonate fragments and sediments that satisfy the spaces created between the skeletons of the corals. Bozec et al. further noted that their model may be slightly simplistic; however, it does take into account information that is currently known, where as a more complex model would be less reliable due to the sheer knowledge gap. Nevertheless, Bozec et al. suggest that local management should aim to sustain high levels of parrotfish grazing in order to maintain Caribbean coral reefs topographical complexity under the current rate of disturbances and trends.
Bozec, Y.-M., Alvarez-Filip, L., Mumby, P.J., 2015. The dynamics of architectural complexity on coral reefs under climate change. Global Change Biology, 21, 223-235