Emergent properties in the responses of tropical corals to recurrent climate extremes.

The frequency, intensity, and spatial scale of climate extremes are changing rapidly due to anthropogenic global warming. A growing research challenge is to understand how multiple climate-driven disturbances interact with each other over multi-decadal time frames, generating combined effects that cannot be predicted from single events alone. Here we examine the emergent dynamics of five coral bleaching events along the 2,300 km length of the Great Barrier Reef that affected >98% of the Reef between 1998 and 2020.

Global warming impairs stock-recruitment dynamics of corals.

Changes in disturbance regimes due to climate change are increasingly challenging the capacity of ecosystems to absorb recurrent shocks and reassemble afterwards, escalating the risk of widespread ecological collapse of current ecosystems and the emergence of novel assemblages. In marine systems, the production of larvae and recruitment of functionally important species are fundamental processes for rebuilding depleted adult populations, maintaining resilience and avoiding regime shifts in the face of rising environmental pressures. Here we document a regional-scale shift in stock-recruitment relationships of corals along the Great Barrier Reef-the world's largest coral reef system-following unprecedented back-to-back mass bleaching events caused by global warming.

Global warming transforms coral reef assemblages.

Global warming is rapidly emerging as a universal threat to ecological integrity and function, highlighting the urgent need for a better understanding of the impact of heat exposure on the resilience of ecosystems and the people who depend on them . Here we show that in the aftermath of the record-breaking marine heatwave on the Great Barrier Reef in 2016 , corals began to die immediately on reefs where the accumulated heat exposure exceeded a critical threshold of degree heating weeks, which was 3-4 °C-weeks. After eight months, an exposure of 6 °C-weeks or more drove an unprecedented, regional-scale shift in the composition of coral assemblages, reflecting markedly divergent responses to heat stress by different taxa.

Spatial and temporal patterns of mass bleaching of corals in the Anthropocene.

Tropical reef systems are transitioning to a new era in which the interval between recurrent bouts of coral bleaching is too short for a full recovery of mature assemblages. We analyzed bleaching records at 100 globally distributed reef locations from 1980 to 2016. The median return time between pairs of severe bleaching events has diminished steadily since 1980 and is now only 6 years.

Environmental drivers of sheltering behaviour in large reef fishes.

Studies of shelter use can provide key insights into the ecology, and structural needs of mobile organisms. Using videos, we examined the usage of tabular corals by large reef fishes, over a 10week period, compared to multiple environmental drivers: visibility, tide (and depth), irradiance, wind speed (as a proxy for wave energy) and water temperature. We found that two of these predictor variables (visibility and wind speed) had a significant effect and together accounted for almost half of the variation in tabular coral usage by fishes.

Global warming and recurrent mass bleaching of corals.

During 2015-2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s. Here we examine how and why the severity of recurrent major bleaching events has varied at multiple scales, using aerial and underwater surveys of Australian reefs combined with satellite-derived sea surface temperatures. The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year.