Great Barrier Reef coral cooked in damaging heatwave

Great Barrier Reef coral cooked in damaging heatwave

Carla Harmon
April 19, 2018

"In comparison, the massive loss of corals from the 2016 marine heatwave was an order of magnitude greater than and more widespread than the patchier, localised damage that typically occurs on reef sites within the track of a severe tropical cyclone", the report said.

"The 2016 marine heatwave has triggered the initial phase of that transition [to heat-tolerant reef assemblages] on the northern, most pristine region of the Great Barrier Reef, changing it forever as the intensity of global warming continues to escalate", the paper said.

The paper says extreme weather events, caused by man-made climate change, are "rapidly emerging as major contemporary threats to nearly all ecosystems", and suggests that while not all corals will be killed off, the shape and variety will be affected.

It means large swaths of mature and diverse clusters have been transformed into a degraded reef structure, Queensland coral reef scientist Professor Terry Hughes says.

Researchers used satellite maps of the geographical patterns of heat exposure and compared them to the coral survival of the 2,300 kilometre Reef.

That's because corals take a long time to recover after bleaching events - the fastest ones might take a decade, while the slower ones take centuries. On the Great Barrier Reef, less than 10% of reefs escaped with no bleaching, compared with more than 40% in previous bleaching events. Warm ocean temperatures stress the corals, causing them to kick out symbiotic algae, which drains the corals of their color.

It was found that of the 3,865 reefs surveyed, an alarming 30 percent had lost two-thirds or more of their coral, significantly reducing their ability to sustain full ecological functioning.

Researchers call for more urgent action to prevent the Great Barrier Reef's decline as a result of climate change.

Global warming's rapid desiccation of the Great Barrier Reef has taken an even more substantial - and permanent- toll than previously understood, a new study has found.

A second heatwave during 2017 also affected the health of the reefs, with nearly half the coral in shallow-water in the northern two-thirds of the Great Barrier Reef killed off, according to the study.

"We saw some corals rapidly dying", explained Dr Scott Heron, another of the study's authors.

"So there is a shift in the mix of species and the overall loss of corals has a broader impact on all the creatures that depend on the corals for food and habitats", Hughes said.

Researchers laid down a transect tape to survey corals on a bleached section of the Great Barrier Reef. "We don't know yet where the larvae are going to come from, and in what numbers".

"When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die". Record higher temperatures in 2016 were followed by another bleaching event this past year.

There are winners and losers among corals as they respond to the accumulating impacts of climate change. Almost half of the coral-around 1 billion animals-died in the past two years, Hughes tells The Washington Post.

Fish species are adjusting to the mass mortality of corals - some better than others.

"We're very concerned that the return period between events is now much shorter than the recovery time required", he told BBC News.

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