There is no shortage of opinions about what the GBR coral loss reported Monday (De’ath et al 2012 in PNAS) means and what we should do about it. Below is a guest post by William Precht. Bill is based in south Florida and recently left the NOAA program to go back to consulting, primarily on coral conservation and restoration projects. He is a carbonate geologist by training and in practice is really more of an expert in reef ecology, restoration, and management. And for a geologist, Bill has a remarkably keen naturalist’s eye. This is his first blog post, ever! Also see pieces by Terry Hughes here and myself here and an interview with Nancy Knowlton here.
William F. Precht, Dial Cordy & Associates, Inc., Miami, FL
The recent paper by De’ath et al. (2012) published in the Proceedings of the National Academy of Sciences, brought to light the sobering fact that over the past 27 years coral cover has declined on the Great Barrier Reef (GBR) by more the 50%, an amount that is significantly greater than originally estimated (Sweatman et al. 2011, but see Hughes et al. 2011), and similar in scope and scale to losses measured in the Caribbean (Gardner et al 2003; Schutte et al 2010). This news is incredibly depressing if you, like me, have always held that as goes the GBR so goes the health of the world’s coral reefs. Whether that view is correct or not matters little if you live, work, dive and play on the GBR. However, the most important aspect of this decline, and one that should not be lost to scientists, conservationists, resource managers, and politicians, is that even on one of the best-studied and best-managed reef systems in the world, coral loss is increasing—even accelerating—at an unsustainable pace.
The authors identified three major causes of coral mortality. These include losses due to (1) coral bleaching, (2) tropical cyclones, and (3) predation by the crown-of-thorns starfish (COTS). Of these, only COTS outbreaks can possibly be controlled or ameliorated by direct, local management actions. Specifically, taking steps to improving water quality can target COTS by reducing their larval survival (Brodie et al. 2005; Fabricius et al. 2010). However, the most striking pattern to emerge from the 27-year data set is not the overall trend of these data, but specifically the trend during the time period from 2006 to the present. During this period coral cover declined at its fastest rate; 1.45% y-1. There are a couple of reasons why these recent data are especially disturbing. First, this is a period of lower than average mortality associated with COTS. Second and more important, this loss follows an expansion of No-Take Areas (NTAs) from 5% to 33% of the Great Barrier Reef Marine Park in 2004, with a parallel focus on improving water quality (Bellwood et al. 2004). Therefore, it appears that local management actions have done little to stem the tide of coral loss or made the GBR more resilient to climate change.
Why are these results so important?
In 2004, Bellwood et al. noted that the single most important management action to increase reef resilience was to significantly increase NTAs and that the GBR network was a good model in that regard. Although I agree that NTAs protect targeted species such as fish, they unfortunately do little to protect most corals from their main sources of mortality (see Jones et al. 2004; Precht et al. 2005; Aronson and Precht 2006; Coelho and Manfrino 2007; Huntington 2011; and Selig et al. 2012 to mention but a few). I find it depressingly ironic that these NTA management actions, touted as a panacea by Bellwood et al. (2004) and Pandolfi et al. (2005), have rendered the reefs they were designed to protect no better off than the average Caribbean reef these authors so eagerly, and incorrectly portrayed a negative light in their reviews.
Understanding where and why corals are dying is critical to implementing appropriate management actions. For instance, Bellwood et al. (2004) commented that the addition of the acroporids in 1999 to the Candidate Species List of the ESA is ‘‘a sad reflection of our inability to implement regional-scale management of Caribbean coral reefs.’’ However, data from throughout the Caribbean indicate that no form of local stewardship or management could have protected these Acropora populations from their major sources of mortality (disease, hurricanes, hyper- and hypothermic stress, and predation) or changed the overall trajectory of coral loss during the past few decades (Schutte et al. 2010). Unfortunately, it appears that the same is true for the GBR.
So what to do?
Clearly, local management actions are an important and effective tool in protecting corals and coral reefs from a great number of anthropogenic stressors. However, if we are to save reefs en masse for future generations we need to get global greenhouse gas emissions under control before it is too late. If not, then the prediction of Aronson and Precht (2006) will be realized, and “local management in vacuo will amount to little more than a series of rear-guard actions, which will at best delay the demise of coral populations and the dissolution of reef ecosystems.” The new data from the GBR should send shock waves to policy advocates, highlighting again the urgency of the coral reef crisis and the need to formulate a global solution.
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Bellwood DR, Hughes TP, Folke C, Nyström M (2004) Confronting the coral reef crisis. Nature 429:827–833.
Brodie J, Fabricius K, De’ath G, Okaji K (2005) Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence. Mar Pollut Bull 51:266–278.
Coelho VR, Manfrino C (2007) Coral community decline at a remote Caribbean island: marine no-take reserves are not enough. Aquat Conserv: Mar Freshw Ecosys 17:666–685.
De’ath G, Fabricius KE, Sweatman H, Puotinen M. (2012) The 27–year decline of coral cover on the Great Barrier Reef and its causes. Proc Natl Acad Sci USA www.pnas.org/cgi/doi/10.1073/pnas.1208909109
Fabricius KE, Okaji K, De’ath G (2010) Three lines of evidence to link outbreaks of the crown-of-thorns seastar Acanthaster planci to the release of larval food limitation. Coral Reefs 29:593–605.
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Hughes TP, Bellwood DR, Baird AH, Brodie J, Bruno JF, Pandol? JM (2011) Shifting base-lines, declining coral cover, and the erosion of reef resilience: comment on Sweatman et al. (2011). Coral Reefs DOI 10.1007/s00338-011-0787-6
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Pandolfi JM, Jackson JBC, Baron N, Bradbury RH, Guzman HM, Hughes TP, Kappel CV, Micheli F, Ogden JC, Possingham HP, Sala E (2005) Are U.S. coral reefs on the slippery slope to slime? Science 307:1725–1726.
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Selig ER, Casey KS, Bruno JF (2012) Temperature-driven coral decline: the role of marine protected areas. Global Change Biol doi: 10.1111/j.1365-2486.2012.02658.x
Sweatman H, Delean S, Syms C (2011) Assessing loss of coral cover on Australia’s Great Barrier Reef over two decades, with implications for longer term-trends. Coral Reefs 30:521–531.