Abstract
Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determining the rates of coral recovery and their long-term responses to increasing sea-surface temperatures is challenging. To do so, we first estimated coral recovery rates following past disturbances on reefs in southern Japan and Western Australia. Recovery rates varied between regions, with the reefs in southern Japan showing more rapid recovery rates (intrinsic rate of increase, r = 0.38 year−1) than reefs in Western Australia (r = 0.17 year−1). Second, we input these recovery rates into a novel, nonlinear hybrid-stochastic-dynamical system to predict the responses of Indo-Pacific coral populations to complex inter-annual temperature cycles into the year 2100. The coral recovery rates were overlaid on background increases in global sea-surface temperatures, under three different climate-change scenarios. The models predicted rapid recovery at both localities with the infrequent and low-magnitude temperature anomalies expected under a conservative climate-change scenario, Representative Concentration Pathway (RCP) 4.5. With moderate increases in ocean temperatures (RCP 6.0) the coral populations showed a bimodal response, with model runs showing either recovery or collapse. Under a business-as-usual climate-change scenario (RCP 8.5), with frequent and intense temperature anomalies, coral recovery was unlikely.
Highlights
Thermal-stress events are changing the composition of many coral reefs worldwide
The recovery rates, or the intrinsic rates of increase, of the coral populations were higher in southern Japan (r = 0.39) than in Western Australia (r = 0.17), again with considerably greater uncertainty for southern Japan than for Western Australia (Table 3)
Forecasting when and where thermal stresses will occur is challenging because of stochastic fluctuations in short-term inter-annual climatic cycles, and because of regional differences in both the ocean temperature and the rates of change in ocean temperature caused by global warming[38,39]
Summary
Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determining the rates of coral recovery and their long-term responses to increasing sea-surface temperatures is challenging. Recovery rates varied between regions, with the reefs in southern Japan showing more rapid recovery rates (intrinsic rate of increase, r = 0.38 year−1) than reefs in Western Australia (r = 0.17 year−1) We input these recovery rates into a novel, nonlinear hybrid-stochastic-dynamical system to predict the responses of Indo-Pacific coral populations to complex inter-annual temperature cycles into the year 2100. Recovery depends on many interacting factors, including species composition and environmental and geographic vicissitudes Understanding these factors and accurately predicting the recovery rates of coral populations is critical in a rapidly changing climate[25], which is characterized by ocean warming and an increase in the frequency of acute thermal-stress events[5]. A system of differential equations captures the dynamics of www.nature.com/scientificreports/ a b
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