Nearly a third of coral in the Great Barrier Reef died during a nine-month period in 2016. The die-off was caused by high sea temperatures.
Image: XL Catlin Seaview Survey
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Australia's Great Barrier Reef suffered a "catastrophic die-off" following an extended heatwave in 2016, according to a study published on Thursday.
Nearly one-third of coral in the 2,300-kilometer-long (1,430-mile) reef system died between March and November 2016, the study published in the journal Nature found.
The massive die-off followed two consecutive years of coral bleaching caused by rising sea temperatures.
Twenty-nine percent of the 3,863 reefs comprising Great Barrier Reef lost two-thirds or more of their coral, with the northern Great Barrier Reef hit particularly hard.
What happens when coral gets stressed? Global warming and environmental changes can cause corals to lose their color, and hinder their ability to feed and reproduce. Scientists and policy makers are sounding alarm bells.
Image: imago/OceanPhoto
Trouble in paradise
Some 2,500 scientists, policymakers and managers came together in Honolulu in June 2016 for the world's largest summit dedicated to the future of coral reefs. With coral reefs threatened by global warming, participants at the 13th International Coral Reef Symposium are calling for a joint rescue effort.
Image: picture alliance/WILDLIFE
World is watching
The event gathered guests from 97 countries, including the presidents of Palau, Micronesia, and the Marshall Islands. Coral reefs are a key source of income in those countries, mostly through tourism.
Image: picture alliance/WILDLIFE
Too warm for comfort
The Pacific nations are worried about the future of their tourist hotspots, as coral reefs face so-called "bleaching" due to rising sea temperatures. "If our coral reefs are further degraded, then our reef-dependent communities will suffer and be displaced," leaders of Palau, Micronesia, and the Marshall Islands said in an open letter.
Image: imago/OceanPhoto
Corals in crisis
Bleaching happens when coral is stressed by hot ocean waters or other changes in the environment. In response, corals may release tiny symbiotic algae which drains them of color. More importantly, bleaching affects their ability to feed and reproduce.
Image: Imago
Pale as death
Severe or prolonged bleaching might kill off corals entirely. Scientists have detected bleached coral in the past two years in oceans around the world. They expect the process to continue thought 2016.
Image: imago/blickwinkel
Giant from Down Under
The 2,300-kilometer-long (1,429-mile-long) Great Barrier Reef is the world's largest coral reef system and its largest living structure. It is also among Australia's main tourist attractions, generating around $3.9 billion (3.5 billion euros) annually.
Image: Imago/ZUMA Press
Tough times for the Great Barrier Reef
Almost one-half of the coral in the reef's northern third have died in the past three months [in 2016], according to James Cook University professor Terry Hughes. The most affected area is remote and unpolluted, with very little fishing and no coastal development. "That's an absolute catastrophe," Hughes said. "There's nowhere to hide from climate change."
Image: Dorothea Bender-Champ for ARC Centre of Excellence for Coral Reef Studies
Fighting for hope
Despite the bad news, scientists claim the problems can be managed with proper funding and political backing. "We are not ready to write the obituary for coral reefs," Professor Hughes said. The scientific community at the conference pledged to work with leaders across the world in order to "curb the continued loss of coral reefs."
Image: imago/OceanPhoto
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The Great Barrier Reef is unlikely to recover. The scientists involved in the study warned the findings signal the large-scale collapse of reef ecosystems as a result of global warming. Reefs cover one percent of the world's oceans, but are home to some 25 percent of marine life and act as fish nurseries.
Fast growing branching coral species with shapes that provide habitat and protection to fish and other marine life faired poorly under heat stress. Although slower growing coral species that are smooth and melon-shaped tended to survive, they, however, do not provide significant habitat for marine life.
"The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining," said study co-author Andrew Baird, a professor at James Cook University.
The scientists said the results of the findings should focus attention on limiting global warming to not more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels and protecting remaining coral systems.
What happens when ocean temperatures rise?
With oceans heating up much quicker than expected, the consequences might affect everything from weather to coral reefs.
Image: picture-alliance/dpa/F. Gierth
Atlantis 2.0
As global warming speeds up, so does the rise in sea levels. While 2004 to 2010 saw oceans rise by about 15 millimeters in total, this value doubled for 2010 to 2016. Tropical regions in the western Pacific are especially affected, threatening many of the coastal areas and low-lying islands with submersion by the end of the century.
Image: picture alliance/Photoshot
Breaking the ice
As ocean and atmospheric temperatures increase, glaciers and ice caps shrink in size. In 2016, the global sea ice extent was 4 million square kilometers (1.54 million square miles) below average. Consequently, more meltwater flows into rivers and oceans, which also causes sea levels to rise.
Image: picture-alliance/dpa/U.Mauder
Losing Nemo
Some ocean regions have already warmed by more than 3 degrees Celsius, upsetting marine ecosystems. Seventy-two percent of demersal fish species in the northeast Atlantic Ocean have so far been affected, with warming limiting their abundance and spread. Species that live in tropical ocean waters, like the clownfish, are also experiencing habitat-related population decreases.
Image: imago/OceanPhoto
Coral bleaching
Warming and acidifying waters affect Nemo's navigation senses, and also threaten his home - coral reefs, one of the most sensitive marine ecosystems. A water temperature increase of as much as 3 degrees Celsius can cause the death of corals and the marine animal species that live in them. Northern parts of Great Barrier Reef have seen coral mortality rates of 50 percent.
Image: imago/blickwinkel
Stormy weather
With increased ocean heat, extremely strong tropical storms are set to occur much more frequently. One of these massive storms was Hurricane Matthew, which hit Haiti in October 2016. The Haitian government put the official death toll at 546, and the hurricane also caused $15 billion (13.8 billion euros) in economic losses on the island nation and in the US, Cuba and the Bahamas.
Image: Reuters/NASA/Alexander Gerst
Heads or tails
There is a strong correlation between atmospheric wind patterns and ocean temperatures, meaning warming waters may also cause the jet stream to get stronger. This could affect airplane travel due to intensified head- and tailwinds. On the upside, this means that some flights may be much faster. On the downside, other flights may take longer and could experience more turbulence.
Image: Fotolia/dell
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"The Great Barrier Reef is certainly threatened by climate change, but it is not doomed if we deal very quickly with greenhouse gas emissions. Our study shows that coral reefs are already shifting radically in response to unprecedented heatwaves," said Terry Hughes, the director of the ARC Centre of Excellence for Coral Reef Studies.
There are still "a billion or so corals alive, and on average, they are tougher than the ones that died. We need to focus urgently on protecting the glass that's still half full, by helping these survivors to recover," he added.
The Great Barrier Reef suffered massive coral bleaching in 1998, 2002, 2016 and 2017.
