Projected changes to growth and mortality of Hawaiian corals over the next 100 years.

Ron K Hoeke,Russell E Brainard,Paul L Jokiel,Robert W Buddemeier

doi:10.1371/journal.pone.0018038

Abstract

BackgroundRecent reviews suggest that the warming and acidification of ocean surface waters predicated by most accepted climate projections will lead to mass mortality and declining calcification rates of reef-building corals. This study investigates the use of modeling techniques to quantitatively examine rates of coral cover change due to these effects.Methodology/Principal FindingsBroad-scale probabilities of change in shallow-water scleractinian coral cover in the Hawaiian Archipelago for years 2000–2099 A.D. were calculated assuming a single middle-of-the-road greenhouse gas emissions scenario. These projections were based on ensemble calculations of a growth and mortality model that used sea surface temperature (SST), atmospheric carbon dioxide (CO2), observed coral growth (calcification) rates, and observed mortality linked to mass coral bleaching episodes as inputs. SST and CO2 predictions were derived from the World Climate Research Programme (WCRP) multi-model dataset, statistically downscaled with historical data.Conclusions/SignificanceThe model calculations illustrate a practical approach to systematic evaluation of climate change effects on corals, and also show the effect of uncertainties in current climate predictions and in coral adaptation capabilities on estimated changes in coral cover. Despite these large uncertainties, this analysis quantitatively illustrates that a large decline in coral cover is highly likely in the 21st Century, but that there are significant spatial and temporal variances in outcomes, even under a single climate change scenario.

Highlights

Anthropogenic climate change has created a dual global threat to reef-building scleractinian corals: (1) mass mortality due to increasingly frequent high temperature events and (2) decreased calcification rates due to increasing atmospheric carbon dioxide (CO2atm) that causes decreasing aragonite saturation state (Va) in surface waters [1,2]
The Coral Mortality and Bleaching Output (COMBO) model was extended by: (1) automating the use of multiple AtmosphereOcean General Circulation Models (AOGCMs) rather than a single Simple Climate Model (SCM) as input; and (2) by replacing the model’s existing coral bleaching module with a more process-based module trained by observations of mortality associated with past bleaching events and based on both the seasonal variability expressed by the different AOGCMs and historical data at specific study locations
Normalized variance of overall ensemble means was not as low (11% in 2050, 9% in 2099), with a very high variance in the standard deviation of outcomes (59% in 2050, and 49% in 2099). This was due to a small number of highly unstable model ensemble members which occurred only at the northern locations (FFS and Midway Atoll (MID))

Summary

Introduction

Anthropogenic climate change has created a dual global threat to reef-building scleractinian corals: (1) mass mortality due to increasingly frequent high temperature events (coral bleaching) and (2) decreased calcification rates due to increasing atmospheric carbon dioxide (CO2atm) that causes decreasing aragonite saturation state (Va) in surface waters (i.e. ocean acidification) [1,2]. Similar to the COMBO model, the extended model utilizes predicted sea temperature, predicted CO2atm, observed coral growth (calcification) rates, and observed mortality linked to mass coral bleaching episodes It diverges most from previous studies by providing multiple predictions of future conditions: multiple runs of 20 structurally-different AtmosphereOcean General Circulation Models (AOGCMs) and a separate Monte Carlo approach are used to provide separate predictions of sea surface temperature (SST) and Va. it diverges most from previous studies by providing multiple predictions of future conditions: multiple runs of 20 structurally-different AtmosphereOcean General Circulation Models (AOGCMs) and a separate Monte Carlo approach are used to provide separate predictions of sea surface temperature (SST) and Va This provides multiple realizations and establishes multi-model (ensemble) means with a range of possible outcomes (a measure of uncertainty) specific to each study location. This study investigates the use of modeling techniques to quantitatively examine rates of coral cover change due to these effects

Methods

Results

Conclusion