Loss of coral reef growth capacity to track future increases in sea level

Abstract

Sea-level rise (SLR) is predicted to elevate water depths above coral reefs and to increase coastal wave exposure as ecological degradation limits vertical reef growth, but projections lack data on interactions between local rates of reef growth and sea level rise. Here we calculate the vertical growth potential of more than 200 tropical western Atlantic and Indian Ocean reefs, and compare these against recent and projected rates of SLR under different Representative Concentration Pathway (RCP) scenarios. Although many reefs retain accretion rates close to recent SLR trends, few will have the capacity to track SLR projections under RCP4.5 scenarios without sustained ecological recovery, and under RCP8.5 scenarios most reefs are predicted to experience mean water depth increases of more than 0.5 m by 2100. Coral cover strongly predicts reef capacity to track SLR, but threshold cover levels that will be necessary to prevent submergence are well above those observed on most reefs. Urgent action is thus needed to mitigate climate, sea-level and future ecological changes in order to limit the magnitude of future reef submergence.

Improving estimates of coral reef construction and erosion with in situ measurements

“…Considering the value of reefs in shoreline protection (Beck et al ), understanding the balance between the growth and destruction of coral reefs is a major research priority (Perry et al ), particularly through the lens of continuing sea‐level rise (Storlazzi et al ). Florida's subtropical reefs may present a canary in a coal mine scenario because reef building throughout the reef tract ceased ~ 3000 yr ago (Toth et al ) and loss of reef elevation has already been documented over the last century (Yates et al ).…”

“…The convergence of evidence suggesting that reef framework is losing elevation in relation to sea level and eroding away faster than it is being produced (Yates et al ; Perry et al ) is alarming. The mechanisms driving the erosion that we measured, both as a loss in mass from the small colonies, and loss in linear height in the large colonies at Hen and Chickens Reef, are likely a combination of external removal of the skeletal surface by excavating, herbivorous fish and internal weakening and removal by cryptic, infesting sponges and microbes.…”

“…For a comparison with these erosion measurements, we also performed benthic and fish species surveys at the same reef in 2017 to evaluate the carbonate budget using the census‐based approach (Perry et al ). Improving estimates of the constructional and deconstructional processes through empirical measurements is paramount to gaining confidence in carbonate budgets that are used to predict reef futures in a time of accelerating climate change and sea‐level rise (Perry et al ).…”

Changing geo‐ecological functions of coral reefs in the Anthropocene

“…47 cm and c . 71 cm are predicted under these scenarios (Perry et al., ). Many reefs are therefore expected to offer less resistance to water flow, thus increasing the risks of coastal erosion and flooding of low‐lying areas, with associated heightened economic and social costs for coastal communities.…”

“…Potential impacts of changing vertical reef accretion and reduced structural complexity on the coastal protection functions that reefs provide. (a) Plot showing reef accretion rates relative to reef rugosity for sites across the tropical western Atlantic ( TWA ) and Indian Ocean ( IO ) regions (data from Perry et al., ) in the context of the Reef Health Index of Harris et al. ().…”