The current growth rate of coral reefs in the tropical western Atlantic and Indian Ocean is just about keeping pace with projected sea-level rise, according to a paper in Nature this week. However, as coral reefs protect tropical and subtropical shorelines around the globe, the study suggests that small island nations may lose a key contributor to coastal protection against flooding and erosion.
Sea-level rises are predicted to elevate water depths above coral reefs and leave shorelines more vulnerable to erosion. These projections, however, lack data on the interaction between local reef growth and sea levels.
Chris Perry and colleagues calculate the vertical growth potential of more than 200 tropical western Atlantic and Indian Ocean reefs and compare these to recent and projected rates of sea-level rise under different Intergovernmental Panel on Climate Change representative concentration pathway (RCP) greenhouse-gas concentration scenarios. Whereas many reefs retain growth rates close to recent sea-level rise trends, few will have the capacity to track the sea-level rises that are projected under RCP 4.5 scenarios without sustained ecological recovery, and under RCP 8.5 scenarios most reefs are predicted to experience mean water-depth increases of more than 0.5 metres by 2100.
The authors also show that other major climate-related issues, specifically coral bleaching, can drive major declines in reef growth potential. Ocean acidification and thermal impacts on calcification also represent additional threats and may inhibit coral growth, thus making shorelines more vulnerable to erosion.