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Coral reefs are astoundingly diverse ecosystems, built through intricate biotic and abiotic relationships. Yet climate change, pollution and over-harvesting are jeopardising not only the beauty and ecology of these systems, but also the food security, livelihoods and wave protection of hundreds of millions of people. This Focus brings together recent research and opinion published in Nature Research journals on the fundamentals of reef systems and how our activities are affecting them.
Twenty years of catch data and habitat surveys in coral reef fisheries in the Seychelles reveal that total yields can be maintained after severe bleaching and associated regime shifts, but the stability of fisheries is reduced.
Experimental removal of corallivorous snails from corals in the Caribbean Sea shows that this local management action can improve coral resilience to severe warming through reducing bleaching severity and post-bleaching tissue mortality.
Exposure of coral reef fishes to environmentally relevant levels of crude oil reveals widespread impairment of cognitive functions related to habitat settlement and antipredator behaviours, in addition to elevated mortality and reduced growth rates.
Biological responses to ocean acidification will depend on variation in tolerance and phenotypic plasticity over different timescales. This study of the spiny damselfish demonstrates the importance of parental variation and transgenerational effects in the response of fish to ocean acidification.
Analysis of 60 sites in three ocean basins suggests that overgrowth of fleshy algae on coral reefs supports higher microbial abundances dominated by copiotrophic, potentially pathogenic bacteria via the provision of dissolved inorganic carbon.
The impact of coral bleaching and mortality is found to reduce aggression in resident butterflyfish. This is linked to the lower dietary percentage of preferred food, nutritionally rich Acropora coral, with a less nutritious diet influencing aggressive behaviour.
The increasing frequency of marine heatwaves suggests that the impacts of successive events may be influenced by previous events. The extent of the 2016 and 2017 bleaching events on the Great Barrier Reef shows that ecological memory played a role in the impacts of the second heatwave.
Analyses of current coral reef growth rates in the tropical western Atlantic and Indian Ocean show that few reefs will have the capacity to track sea-level rise projections under Representative Concentration Pathway scenarios without sustained ecological recovery.
Fish and invertebrate communities transformed across the span of the Great Barrier Reef following the 2016 bleaching event due to a decline in coral-feeding fishes resulting from coral loss, and because of different regional responses of key trophic groups to the direct effect of temperature.
Acute heat stress from the extended marine heatwave of 2016 is a potent driver of the transformation of coral assemblages, which affects even the most remote and well-protected reefs of the Great Barrier Reef.
Overfishing and nutrient pollution can damage coral reefs in part by increasing coral-algal competition. Here the authors simulate these stressors in a three year field experiment, and show that they interact to enhance sensitivity to temperature, predation and bacterial opportunism.
It has been suggested that deep coral reefs offer a refuge against warming and mass bleaching. Here Frade et al. look at the 2016 bleaching event in the northern Great Barrier Reef and found that deep reefs initially acted as thermal refuges, though this effect lessened in the late summer months.
Hannah Barkley and Anne Cohen and colleagues used bleaching signatures in coral skeletons to examine the Jarvis Island coral community response to multiple El Niño heatwaves. They find the historically productive ecosystem experienced 10 bleaching events in the past 60 years and its recovery provides insights into coral reef resilience under ocean warming.