Avoiding Coral Reef Functional Collapse Requires Local and Global Action

This paper uses modeling on Caribbean reefs to emphasize the need for both local action and a low-carbon economy to prevent further degradation of coral reefs. The authors find that no-take marine reserves (leading to protection of herbivorous fish) must be combined with low carbon emissions (keeping the global mean temperature below 2 degrees Celsius) to prevent erosion of coral skeletons. Additionally, they found that coral reefs must be initially relatively healthy (they use a measure of 20% coral cover) to start, even with lowered carbon emissions and no-take reserves. This paper provides a clear message that global action to reduce carbon emissions must go hand-in-hand with local efforts, such as no-take reserves and watershed protection.

Author: Kennedy, E.V., C.T. Perry, P.R. Halloran, R. Iglesias-Prieto, C.H.L. Schonberg, M. Wisshak, A.U. Form, J.P. Carricart-Ganivet, M. Fine, C.M. Eakin, and P.J. Mumby
Year: 2013
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Current Biology  23(10): 912–918

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Coral Reefs Under Rapid Climate Change and Ocean Acidification

Levels of atmospheric CO2 continues to rise and threaten coral reefs globally. This is because atmospheric CO2 reacts with water in the ocean to produce carbonic acid which in turn forms bicarbonate ions that react with carbonate ions to produce more bicarbonate ions (reducing availability of carbonate in the ocean). Declines in available carbonate can reduce the calcification of coral reefs and marine organisms. The authors describe the consequences of increased atmospheric CO2 and subsequent warming, as predicted. Even under the best case scenario, ocean acidification will likely cause contractions of carbonate coral reefs if CO2 levels exceed 500 ppm. Although these global threats require changes at a global scale, local factors such as poor water quality, coastal pollution, and overexploitation of certain organisms, should be reduced to lesson the overall stressors to coral reef communities. The authors also suggest that healthy grazing populations should help to improve a coral reefs ability to bounce back from future disturbances; thus, healthy herbivore populations should be managed for explicitly.

Author: Hoegh-Guldberg, O.,  P.J. Mumby, A.J. Hooten, R.S. Steneck, P. Greenfield, E. Gomez, C.D. Harvell, P.F. Sale, A.J. Edwards, K. Caldeira, N. Knowlton, C.M. Eakin, R. Iglesias-Prieto, N. Muthiga, R.H. Bradbury, A. Dubi, and M.E. Hatziolos
Year: 2007
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Science 318(5857): 1737-1742. doi: 10.1126/science.1152509

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Spatial Variation in the Functional Characteristics of Herbivorous Fish Communities and the Resilience of Coral Reefs

This study explores the importance of herbivore functional roles and their diversity and abundance when predicting coral reef resilience to undesirable phase-shifts to algal-dominated reefs. Authors looked at reef slopes on 92 reefs through the Great Barrier Reef, Australia. Results showed 11 reefs resisted phase shifts after disturbance, however without high herbivore function. This data suggests other environmental factors may compensate for herbivores that enhance reef resilience, specifically including water clarity and quality. Authors of this study argue spatially explicit strategies should consider both the functional characteristics of local herbivore communities and environmental factors in order to create lower resilience thresholds

Author: Cheal, A. J., M. Emslie, M.A. MacNeil, I. Miller, and H. Sweatman
Year: 2013
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Ecological Applications 23(1): 174–188

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Ocean Acidification and Warming will Lower Coral Reef Resilience

In this study, the authors quantitatively analyzed how different combinations of CO2 and fishing pressure on herbivores will affect the ecological resilience of a benthic reef community consisting of three common groups: branching corals, fleshy macroalgae and turfs (free space for coral and algal colonization). Resilience was defined by the community’s capacity to maintain and recover to coral-dominated states. They developed a dynamic community model that was run for changes in sea surface temperature and water chemistry predicted by the rise in atmospheric CO2 projected from the IPCC’s fossil-fuel intensive scenario during this century. The findings demonstrate, using on the dynamics of a species pair of corals (Acropora) and fleshy macroalgae (Lobophora), that the effects of ocean acidification and warming on coral growth and mortality will have important impacts on coral reef resilience under increasing CO2. Specifically, by reducing coral growth (due to acidification) and survivorship (due to warming), increasing CO2 will lower the threshold value at which local and regional processes like herbivore overfishing and nutrification drive the study community from predominantly coral-dominated to predominantly algal-dominated states. Therefore, warming, acidification, overfishing and nutrification all drive the dynamics of the system in the same direction, suggesting that reduced coral resilience in a high-CO2 world is likely to be a consequence of both global threats and local-scale disturbances

Author: Anthony, K.R.N., J.A. Maynard, G. Diaz-Pulido, P.J. Mumby, P.A. Marshall, L. Cao, and O. Hoegh-Guldberg
Year: 2011
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Global Change Biology 17(5): 1798-1808. doi:10.1111/j.1365-2486.2010.02364.x

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