Story at a glance
- Widespread mass bleaching is damaging the Great Barrier Reef off the coast of Australia.
- This is the third such recent event in the region, following similar events in 2016 and 2017.
- The bleaching was caused by heat accumulation, particularly through February of this year, although there has been cooler weather in recent weeks.
The Great Barrier Reef is seeing the most widespread mass bleaching ever, threatening more coral life than similar events in 2016 and 2017.
Aerial surveys of the reef's roughly 344,000 square kilometers show bleaching across large areas, including moderate or severe bleaching in some southern areas that saw little or no bleaching in 2016 and 2017. While key tourism reefs in the northern and central areas experienced only moderate bleaching, the southern part of the Marine Park was severely damaged.
Bleaching doesn’t necessarily kill coral life, and corals on mildly or moderately bleached reefs have a good chance of surviving and recovering. But some corals affected by bleaching in 2016 and 2017 still haven't regained their color and health.
The phenomenon refers to the death of zooxanthellae — a type of single-celled organism occurring in large numbers amongst marine life — when the surrounding sea temperature becomes too warm. These colorful marine algae live inside corals and are the primary source of their energy and color. When zooxanthellae die, the coral tissue becomes transparent, appearing "bleached." Corals can regain zooxanthellae if temperatures return to normal levels, but the stress can decrease growth and reproduction.
“Dead corals don’t make babies,” said lead author Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, in a release. “The number of new corals settling on the Great Barrier Reef declined by 89 percent following the unprecedented loss of adult corals from global warming in 2016 and 2017.”
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The Great Barrier Reef Marine Authority said they are studying the surveys in comparison to previous events, but due to COVID-19 travel and social distancing restrictions, on-water operational activity is limited.
At the same time, the reef is still under pressure from heat stress that accumulated over this past summer in the Southern Hemisphere, particularly in February and early March.
"Climate change remains the single greatest challenge to the reef. While the strongest possible global efforts to reduce emissions are essential, it is critically important we continue to deliver the work already being undertaken to enhance the resilience of the reef," the marine park authority said in a statement.
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