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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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Email for the full article: resilience@tnc.org

Science 318(5857): 1737-1742. doi: 10.1126/science.1152509

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Heterotrophic Plasticity and Resilience in Bleached Corals

This paper aims to understand the mechanisms responsible for differential success of various coral species after bleaching. The following species were examined: branching corals including Montipora capitata and Porites compressa, and the mounding coral Porites lobata. Results indicate that M. capitata was more resilient to bleaching as they were able to meet their daily metabolic energy requirements by increasing feeding rates and percent contribution of heterotrophically acquired carbon to daily animal respiration (CHAR). Therefore, high CHAR capabilities may be contributing to higher coral resilience to bleaching events. Frequent bleaching may also select for higher CHAR capabilities in the future.

Author: Grottoli, A.G., L.J. Rodrigues, and J.E. Palardy
Year: 2006
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Nature 440: 1186-1189. doi:10.1038/nature04565

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Coral Reef Resilience and Resistance to Bleaching

A comprehensive overview and synthesis of coral bleaching and potential effects of climate change, discussions regarding the meaning of resistance and resilience, and future research opportunities are presented here. This papers reviews initiatives that are working on coral reef resilience and provides information on tools and management strategies. Additionally, a comprehensive glossary of relevant terms is provided. This document is an invaluable resource for MPA practitioners. 

Author: Grimsditch, G.D. and R.V. Salm
Year: 2005
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Produced by the IUCN World Conservation Union

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Coral Reef Recovery Dynamics in a Changing World

The authors quantitatively reviewed the literature (55 studies in total) on the recovery rates of coral reef ecosystems from acute disturbance events among 48 different reef locations (from western Indian Ocean, to eastern Pacific and the Caribbean) and assessed which characteristics promote faster recovery rates. Specifically, the authors tested the relative roles of disturbance characteristics, reef characteristics, connectivity and anthropogenic influences. The main purpose was to understand the factors that drive inter-reef variations in recovery trajectories. Information on ecological characteristics thought to be important for recovery were assessed including: coral diversity, percent cover of different life-forms, structural complexity, fish diversity, density and biomass (including densities of different functional groups and algal cover).

The authors found that of those reefs that have been recovering from acute disturbances (and thus are resilient), the greatest predictors of rate of recovery were geographic region, management status and severity of disturbance. Coral recovery was slowest in the eastern Pacific and fastest in the western Pacific (higher functional diversity of corals and fish in the western Pacific is thought to promote capacity to recover). The study found no evidence of small-scale connectivity, as measured as distance to nearest reef and number of neighbor reefs, influencing recovery rates. However, distance may not always capture variation among locations affectively. There was evidence of slower recovery rates within protected areas compared with other management regimes and fished areas. It is important to note that potential predictors of recovery like herbivore biomass, fish functional diversity and habitat structural complexity were not document in the studies evaluated. A better understanding of these processes may enable more appropriate management actions

Author: Graham, N.A.J., K.L. Nash, and J.T. Kool
Year: 2011
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Coral Reefs 30(2): 283-294. doi: 10.1007/s00338-010-0717-z

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Most Corals May Not Change Their Symbionts

This paper tests the hypothesis that corals can adapt to climate change by exchanging algal types. Data from 43 studies including 442 coral species (stony coral and octocoral) documents that only a minority of coral species are able to change symbionts. The majority of coral species are host to only one zooxanthella clade, and this clade does not change over time. Additionally, these corals do not change algal clades with additional stressors or when transplanted in different environments. Therefore, the majority of coral species do not appear to exhibit algal switching. This paper suggesting that only a small subset of symbiotic corals will survive if global warming continues.

Author: Goulet, T.L.
Year: 2006
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Marine Ecology Progress Series 321: 1-7. doi:10.3354/meps321001

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Long-term Effects of the 1998 Coral Bleaching Event on Reef Fish Assemblages

This paper examined the effects of the 1998 coral bleaching event on fish assemblages by measuring fish abundance, taxonomic richness, and functional group abundances (i.e. obligate corallivores, facultative corallivores, coral dwellers, benthic invertebrate feeders, roving herbivores, territorial herbivores). These variables were compared to habitat and site differences over time. Initially, the authors saw a significant increase in total abundance and taxonomic richness after only 6 months in one site. However, both measures decreased at both sites after 6 years. These discrepancies indicate the need for long term monitoring. Additionally, the long term declines experienced by both sites post bleaching create cause for concern for the long term impacts of bleaching on coral reef communities

Author: Garpe, K.C. , S.A.S. Yahya, U. Lindahl, and M.C. Öhman
Year: 2006
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Marine Ecology Progress Series 315: 237-247. doi:10.3354/meps315237

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Global Assessment of Coral Bleaching and Required Rates of Adaptation Under Climate Change

The authors of this paper conducted a global assessment of coral bleaching by adapting the NOAA Coral Reef Watch bleaching predation method. The results of their model suggest that most coral reefs will be exposed to annual or biannual bleaching events and will need to increase the thermal tolerance of their symbionts by 0.5-1° in the next 30-50 years based on minimum levels of warming. When moderate estimates of warming are made (based on increased emissions) total thermal adaptation may exceed possible level. Therefore, emissions play an important role in determining the likelihood for coral reef persistence.

Author: Donner, S.D., W.J. Skirving, C.M. Little, M. Oppenheimer, and O. Hoegh-Guldberg
Year: 2005
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Global Change Biology 11: 2251-2265. doi: 10.1111/j.1365-2486.2005.01073.x

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Does Herbivorous Fish Protection Really Improve Coral Reef Resilience? A Case Study from New Caledonia (South Pacific)

The authors assessed populations of herbivorous fish in 14 reefs around New Caledonia and found that the current low fishing pressure doesn’t affect the population of macroalgae feeders. Therefore, they conclude that regulating the fishery would have a high social cost and minimal impact in mitigating the impacts of climate change.

However, they do point out that the mining industry is a major chronic stress factor, and should be regulated, rather than regulating fisheries. They found huge regional variation in the development of macroalgae development on corals after disturbances, from 11% of case studies in the Pacific, to 50% in the Indian Ocean, to 67% in the Caribbean, and conclude that regulating macroalgae-feeding fish populations (via MPAs or fisheries regulations) has highly variable impacts throughout the world.

Author: Carassou, L., M. Leopold, N. Guillemot, L. Wantiez, and M. Kulbicki
Year: 2013
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PLoS ONE 8(4): e60564. doi:10.1371/journal.pone.0060564

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Impact of Herbivore Identity on Algal Succession and Coral Growth on a Caribbean Reef

This study conducted two experiments over two years to evaluate how herbivore identity and species richness affected the recruitment and primary succession of algal communities and the cascading effects on coral growth. Equal densities and masses of either single-species or mixed-species of herbivorous fishes were enclosed in replicate, 4m2 cages at a depth of 17m on a reef in the Florida Keys, and algal community development and coral growth on new substrates was monitored.

Findings showed that for communities undergoing primary succession (similar to new substrates created following coral death from bleaching, disease, or storm damage), strong species-specific effects of herbivores limit the abundance of late-successional algae and facilitate early successional species such as filamentous algal turfs. Herbivore richness effects were strong on established communities due to complementarity feeding among fish species; this complementary feeding not only impacted seaweeds, but also enhanced coral survivorship and growth. Species-specific effects of herbivorous fishes suggest that a species-rich herbivore fauna can be critical in providing the resilience that reefs need for recovery from common disturbances such as coral bleaching and storm damage.

Author: Burkepile, D. E. and M. E. Hay
Year: 2010
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PLoS One (5)1: e8963. doi:10.1371/journal.pone.0008963

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