Coral reefs

One of the most visible impacts of current climate change is the catastrophic bleaching and death of corals in reefs around the world. This issue of Nature Ecology & Evolution and an online Focus highlight recent research documenting the transformation of these systems.

Sixteen-month manipulation experiments in a degraded macroalgae-dominated tropical reef setting show that lower coral species richness suppresses growth and survivorship of multiple species.

Large-scale phylogenetic analysis of coral reef fish species shows that functional traits evolve fastest in those at high and low trophic levels with narrow diet breadth.

What are the molecular mechanisms underpinning local adaptation? Reciprocal transplant of mustard hill coral from a variable to a more stable habitat demonstrates that populations exhibit phenotypic signatures consistent with local adaptation.

Larval dispersal of clownfish and butterflyfish across a 10,000 km² area was tracked over 2 years, a large enough scale to inform the design of marine reserve networks and test their performance.

High-throughput metabarcoding of coral reef fish larvae from the Red Sea enables species-level reconstruction of the highly biodiverse larval community, and their spatio-temporal distribution and abundance.

The Great Barrier Reef has migrated rapidly in response to sea-level changes since the last glacial period, suggesting resilience to environmental stress over this interval, according to a reconstruction of reef accretion.

Deep reefs and their inhabitants are diverse, but environmental change, in particular warming, will cause these reefs found along southeastern Australia to tropicalize with different responses across functional groups, resulting in novel communities by the 2060s.

Productivity of coral reefs is enhanced near islands with no invasive rats, as populations of seabirds, which transfer nitrogen from deeper areas of ocean to the nearshore waters via their guano, are much larger than on rat-infested islands.

Coral-associated microbes could enhance the capacity of their host organism to respond to environmental change. Ziegler and colleagues use a reciprocal transplant experiment to show that microbiomes of heat-tolerant corals are more resilient to change than those of heat-sensitive corals.

Huanle Liu et al. report draft genomes of two Symbiodinium species, one from the most dominant type of symbionts in reef-building corals. They find evidence of positive selection in genes related to stress response, meiosis and other traits required for forming successful symbiotic relationships.

Michael Ochsenkühn et al. look at the microbial and metabolic composition of coral surfaces and the surrounding seawater. They find that the metabolites found on the surface of the coral create a concentration gradient that influences the surrounding microbiome.

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.

An integration of 20 years of data on fisheries catch and reef habitat characteristics shows how bleaching-induced shifts in reefscapes change species abundances but may not impair total catch capacity.

Rapid evolution of morphological variations is shown to be linked to positions of coral reef fishes at trophic-web extremes. This finding suggests that current fishing practices on coral reefs that target top predators and seaweed-grazing fishes may undermine the potential for future species diversification.

The importance of biodiversity for productive community functioning is emerging as one of a very few general rules in ecology, but evidence has been sparse that it applies in tropical coral reefs—until now.

We anticipate that conventional management approaches will be insufficient to protect coral reefs, even if global warming is limited to 1.5 °C. Emerging technologies are needed to stem the decline of these natural assets.

Coral biologist and tireless reef advocate.

An assessment of the capacity of coral reefs to grow fast enough to keep up with projected rises in sea level finds that most reefs will fall behind if nothing is done to restore them.

The introduction of non-native rats can devastate island ecosystems. It now emerges that these rats also harm a complex web of interactions linking seabirds with the algae and fishes of nearby coral reefs.

Caroline Palmer proposes the concept of coral holobiont damage thresholds to stimulate research into coral health and immunity as tropical reefs are increasingly threatened by climate change. This framework may be used to develop targeted approaches to coral reef restoration, management and conservation.

Marine protected areas can support ecosystem resilience in the face of environmental stress, but only up to a point.