[Coral-List] Guardian Article on Recent Studies by Cinner et al & Bruno & Valdivia

Bruno, John jbruno at unc.edu
Fri Aug 12 13:45:27 EDT 2016

Dear Avigdor,
Thank you for your feedback. We look forward to reading your response in Scientific Reports. Below we respond to some of your comments in an attempt to clarify things for readers of the coral-list. We posted a few graphics and the Lit Cited here: http://theseamonster.net/2016/08/response-to-avigdor-abelson/
1) As we explained in the paper, the reason we and many others (e.g., Williams et al. 2008, 2015, Knowlton and Jackson 2008, Sandin et al. 2008, Mora 2008, Cinner et al. 2013, Jackson et al. 2014, Smith et al. 2016) used human population presence or density as a proxy for the presence or magnitude of local stressors is that actual data on those stressors is non-existent for all but a few locations. We all wish that weren’t the case, but it’s just the reality. Moreover, the fact is that more people generally means a larger human footprint on the landscape and seascape (see Sanderson et al. 2002, Mora et al. 2011), e.g., human population density is a good predictor of fishing intensity and fish biomass (see Warren-Rhodes et al. 2003, Hawkins and Roberts 2004, Newton et al. 2007, Sandin et al. 2008, Stallings 2009, Williams et al. 2011, Nadon et al. 2012, Cinner et al. 2013, Duffy et al. 2016 and many others). Too many people are one of the core problems reefs are facing, and it’s an ultimate, rather than a proximate cause. So in some ways, we believe it’s better that we focus on it, rather than indicators of human overpopulation like overfishing. On the other hand, we acknowledge things can get tricky when management policy, the intensity of economic activity, global trade, etc. decouple population density from local impacts.
Even if you reject the use of human population density as an indicator of local human stressors, you could just focus on the state of the world’s isolated reefs: the logical inferences still hold. If local impacts were generally substantially greater in magnitude or if the effects of local and global impacts were synergistic, isolated reefs with few or no human residents should have more coral and less algae. But they don’t. Therefore, the logical inference is that global warming is a primary if not the primary driver of coral loss around the world. We put a simple graphic on the blog post to illustrate the logic of this test and the inductive inferences and management strategies the results lead to.
2) We’ve reanalyzed the data using the Global Human Influence Index dataset and again found no relationship between coral cover and human transformation of the coastal landscape. This is a comprehensive index created from nine global data layers that takes into account human population density, built-up infrastructure, land use (agriculture), nighttime lights, land cover, and human access such as the amount of coastlines, roads, railroads and navigable rivers. Details and graphics are on the blog.

3) All three studies that have tested this hypothesis (that isolated reefs have more coral and less macroalgae) have failed to reject the null of no relationship, i.e., ours, Smith et al. (2016) and Jackson et al. (2014). No published study (with a reasonable sample size) has found that in general, isolated reefs have higher coral cover. Some clearly do. But so do many reefs adjacent to overpopulated, intensively developed coasts where presumably local impacts are substantial.
4) We don’t agree that our argument that warming is a major cause of coral loss is somehow untested or unsupported. In an earlier paper (Selig, Casey & Bruno 2012) , we clearly showed using an extended version of this database (same sites, more years) that ocean warming caused a major decline in coral cover over the last several decades on these reefs. So we did examine the putative global driver (temperature anomalies) and showed it was a likely cause of the observed pattern. We explained this in the paper. And there are of course countless smaller-scale studies demonstrating the effects of thermal extremes on coral cover.
5) It’s true that science is often used and misinterpreted by the media and others to advance policy positions. But this is true of any science. For example, climate change denier blogs like CO2Science frequently use studies demonstrating local threats to reefs (e.g., sunscreen studies) to argue ocean warming doesn’t matter and that carbon emissions don’t need to be limited. Similarly, the “parrotfish restoration can buy reefs time” argument could be used to delay policies to reduce greenhouse gas emissions. All of our science is both used and abused by advocates for the environment, big oil, etc.  We have been very clear that we strongly support local management to mitigate local problems, including threats to corals, to human health and well-being, and to improve fisheries management. If it were up to us, we’d ban fishing from 30-50% of the oceans; but to protect and restore biodiversity (e.g., of large vertebrates), not to conserve corals. Bottom line; yes, scientists have to be cautious, but they also have to report their results unapologetically.
6) We neither found nor said (as you implied) that that there is no evidence of local impacts. There clearly is. They clearly matter. Instead, our results suggest that either local impacts are swamped by warming or that local and global threats have antagonistic effects (our results do not distinguish between the two alternative explanations). Local protection is important. But as warming progresses, it’s becoming more and more obvious that reducing emissions is crucial. Another way to put it is that local protection is necessary but not sufficient.
7) This finding is neither novel nor radical. Dozens of studies indicate local fisheries restrictions (and other local management actions) do not protect corals from ocean warming and acidification. Many people have been saying this on the coral-list for many years. And numerous reef scientists have argued more eloquently and forcefully than us that the only effective solution to mitigating the impact of warming on reefs is to radically reduce carbon emissions (Jameson et al. 2002, Aronson and Precht 2006, Côté and Darling 2010, Mora and Sale 2011). Moreover, to quote Rich Aronson “another way radical, unacceptable ideas can become acceptable is if they turn out to be correct”. Given the mountains of evidence, this idea should be widely embraced by our field, policy makers, and reef managers. We need to stop kidding ourselves: to protect and restore coral populations we need to immediately reduce carbon emissions. In the short term, local threats are certainly important. As many people have said, it’s not either or – it’s all of the above. But the fact is, in the long run, local management won’t matter at all if we fail to limit warming. There literally won’t be any corals left to manage. The perfect example is the Florida Keys reef track, where, after decades of intensive management, coral cover is still less than 5% (and declining). We have only a few decades or a human lifetime at most. IPCC models indicate that under the business as usual emissions scenarios (A2/RCP 8.5), tropical oceans will have warmed by nearly 3ºC (beyond the nearly 1ºC of warming to date) by the end of this century. That means normal summertime temperatures on most reefs of ~32ºC or 33ºC and peak anomalies of 35ºC or greater – well beyond the physiological limits of most coral species and of many other reef inhabitants. If you think parrotfishes and watershed management can protect corals and other reef inhabitants from that reality, no data I show you is going to change your mind.
John and Abel
Literature Cited are here: http://theseamonster.net/2016/08/response-to-avigdor-abelson/

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