Last updated April 19, 2018 at 10:59 am
A recent heatwave has transformed the Great Barrier Reef, and not for the better.
Corals on the Great Barrier Reef experienced a catastrophic die-off following the extended marine heatwave of 2016, transforming the ecological functioning of almost a third of the world’s largest reef system.
Researchers from James Cook University in Townsville say their findings reinforce the need for risk assessment for reef ecosystem collapse, especially if global action on climate change fails to limit warming to 1.5‒2 °C above pre-industrial levels.
Professor Terry Hughes and colleagues mapped the geographical pattern of heat exposure and resultant coral death along the full 2300 kilometres of the reef. They found that many corals died immediately from the heat stress, but others died more slowly following the depletion of their zooxanthellae — the yellowish brown symbiotic algae that live within most reef-building corals.
The different colour morphs of Acropora millepora, each exhibiting a bleaching response during mass coral bleaching event. Credit: ARC Centre of Excellence for Coral Reef Studies/ Gergely Torda
Coral death was highly correlated with the amount of bleaching and level of heat exposure, with the northern third of the reef most affected. The coral die-off also led to radical changes in the composition and functional traits of coral assemblages on hundreds of individual reefs, with mature and diverse assemblages transformed into more degraded systems.
The authors note that a full recovery to the pre-bleaching assemblages is unlikely to occur, because many surviving coral colonies continue to die slowly, and the replacement of dead corals will take at least a decade even for fast-growing species. Moreover, the Great Barrier Reef experienced severe bleaching again in 2017, causing further extensive damage.
As such, coral reefs throughout the tropics are likely to continue to degrade until climate change stabilises, allowing remnant populations to reorganise into heat-tolerant reef assemblages.
The paper was published in Nature with an accompanying letter.
Video courtesy of ARC Centre of Excellence for Coral Reef Studies.
