Coral bleaching is the detrimental expulsion of algal symbionts from their cnidarian hosts, and predominantly occurs when corals are exposed to thermal stress. The incidence and severity of bleaching is often spatially heterogeneous within reef-scales (<1 km), and is therefore not predictable using conventional remote sensing products. Here, we systematically assess the relationship between in situ measurements of 20 environmental variables, along with seven remotely sensed SST thermal stress metrics, and 81 observed bleaching events at coral reef locations spanning five major reef regions globally. We find that high-frequency temperature variability (i.e., daily temperature range) was the most influential factor in predicting bleaching prevalence and had a mitigating effect, such that a 1 °C increase in daily temperature range would reduce the odds of more severe bleaching by a factor of 33. Our findings suggest that reefs with greater high-frequency temperature variability may represent particularly important opportunities to conserve coral ecosystems against the major threat posed by warming ocean temperatures.

SignificanceMarine reserves that prohibit fishing are a critical tool for sustaining coral reef ecosystems, yet it remains unclear how human impacts in surrounding areas affect the capacity of marine reserves to deliver key conservation benefits. Our global study found that only marine reserves in areas of low human impact consistently sustained top predators. Fish biomass inside marine reserves declined along a gradient of human impacts in surrounding areas; however, reserves located where human impacts are moderate had the greatest difference in fish biomass compared with openly fished areas. Reserves in low human-impact areas are required for sustaining ecological functions like high-order predation, but reserves in high-impact areas can provide substantial conservation gains in fish biomass.

This study explores the social, economic, and ecological context within which communities in Papua New Guinea and Indonesia use adaptive coral reef management. We tested whether periodic closures had positive effects on reef resources, and found that both the biomass and the average size of fishes commonly caught in Indo-Pacific subsistence fisheries were greater inside areas subject to periodic closures compared to sites with year-round open access. Surprisingly, both long-lived and short-lived species benefited from periodic closures. Our study sites were remote communities that shared many socioeconomic characteristics; these may be crucial to the effectiveness of adaptive management of reef resources through periodic closures. Some of these factors include exclusive tenure over marine resources, a body of traditional ecological knowledge that allows for the rapid assessment of resource conditions, social customs that facilitate compliance with closures, relatively small human populations, negligible migration, and a relatively low dependence on fisheries. This dynamic adaptive management system, in which communities manage their resources among multiple social and ecological baselines, contrasts with western fisheries management practices, centered on maintaining exploited populations at stable levels in which net production is maximized.

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Threats from climate change and other human pressures have led to widespread 21 concern for the future of Australia's Great Barrier Reef (GBR) 1 , where increasingly 22 frequent and severe coral bleaching, fishing, and ongoing pollution are 23 undermining long-term persistence of coral-dominated reefs 2,3 . Future resilience 24 of coral-dominated reefs within the GBR will be determined by their ability to 25 resist disturbances and to recover from coral loss, generating intense interest in 26 management actions that can moderate these processes 4-7 . Here we quantify the 27 effect of environmental and human drivers on the resistance and recovery of hard 28 corals to multiple disturbances within the southern and central GBR. Using a 29 composite index for water quality, we find that reefs exposed to poor water quality 30 recover from disturbance more slowly and are more susceptible to outbreaks of 31 crown-of-thorns starfish and coral disease while also being more resistant to 32 coral bleaching. Protection from fishing and increased herbivory were not 33 associated with substantially faster recovery from disturbance. Water quality 34 mediation of a tradeoff between resistance and recovery illustrates that, while 35 reefs in waters of chronically-poor quality contain corals with greater bleaching 36 resistance, there is a net negative impact on recovery and long-term hard coral 37 cover. Given these conditions, we find that 11-23% improvements in water quality 38 will be necessary to bring recovery rates in line with projected increases in coral 39 bleaching among contemporary inshore and mid-shelf reefs. However such 40 reductions are unlikely to buffer projected bleaching effects among outer-shelf 41 GBR reefs dominated by fast growing, thermally sensitive corals, demonstrating 42 practical limits to local management of the GBR against the effects of global 43 warming. 44 45 46The Great Barrier Reef (GBR) has experienced unprecedented losses of hard coral cover 8 . Most 47 coral loss on the GBR has been due to acute disturbances including storms 9,10 , disease 11 , 48 outbreaks of crown-of-thorns starfish Acanthaster spp. (CoTS) 9 , and coral bleaching 8 . Many of 49 these impacts are predicted to become more frequent or intense due to climate change 2,10,12-14 . 50Key to long-term coral-dominance on reefs is whether coral communities can resist coral loss and 51 recover sufficiently quickly between successive disturbances to be resilient and sustain viable 52 populations 15 . However, there are currently few process-based models for quantifying intrinsic 53 rates of increase that accurately characterize recovery. Some of the key drivers thought to 54 influence coral cover recovery include rates of herbivory 16 , coral community composition 17,18 , 55 water quality 19-22 , and protection from fishing 23 . While research into individual drivers is well 56 developed, how cumulative stressors may interact under climate change is not; the potential for 57 non-linear responses to novel ecosystem states creates consid...