Great Barrier Reef has lost half its coral

By Joanna Egan 29 November 2013
Reading Time: 4 Minutes Print this page
Australia’s iconic reef has lost a staggering amount of coral in the past 27 years, say experts.

THE GREAT BARRIER REEF is one of the planet’s most famous natural wonders, stretching across 348, and comprised of more than 2900 separate reefs. But disturbing new research reveals it has lost half its coral cover since 1985.

The study from the Australian Institute of Marine Science (AIMS), published today in the US journal the Proceedings of the National Academy of Sciences, provides a dim view of the reef’s future.

“Coral cover on the GBR is consistently declining, and without intervention, it will likely fall to 5 to 10 per cent within the next 10 years,” say the authors of the report. “Without intervention, the GBR may lose the biodiversity and ecological integrity for which it was listed as a World Heritage Area.”

Three major causes of Great Barrier Reef decline

The study is based on data collected by a reef monitoring program that began in 1985 and looked at 214 reefs in 2,258 separate surveys. It showed a 50.7 per cent decline in reef cover between 1985 and 2012.

The authors of the report cite three major causes for the decline: tropical cyclones caused 48 per cent of the loss, coral predation from crown-of-thorns starfish (Acanthaster planci) led to another 42 per cent, and coral bleaching was responsible for the final 10 per cent.

“The shocking thing about the research is that this downward turn in coral cover has occurred in the world’s most sophisticated marine management park,” says Professor Ove Hoegh-Guldberg, who heads up the Coral Reef Ecosystems Lab at the University of Queensland. “We’re not talking about reefs that have been under extreme environmental stresses, such as those in Southeast Asia; it’s happening in this well-managed marine park and it’s happening very rapidly.”

All three of the drivers causing the coral decline are related to climate, says Ove, who was not involved in the study. Bleaching is caused by extreme heat events and rising sea temperatures, and there’s growing evidence to suggest warmer seas are leading to more intense tropical storms and more intense flooding of the sort we saw two years ago.

Controlling crown of thorns is key

Resultant flooding washes nutrients and sediments into the ocean, which causes increases in phytoplankton favouring the larvae of crown-of-thorns starfish and leading to potential population explosions, Ove told Australian Geographic. “More work is required to understand this link, but that is where it appears to be headed,” he says.

The report says that while mitigating the effects of climate change and ocean acidification are necessary for the long-term conservation of the reef, improving water quality and taking other measures to control the crown-of-thorns starfish are the most immediate goals.

Former AIMS research director Dr Peter Doherty says that controlling the starfish, which has few natural predators, is crucial to ensuring the future of the reef. Adults feed on live coral, and a single starfish can consume up to 10sq.m in a year.

“The starfish represents the main management lever that we haven’t yet pulled,” Peter says. “If we could prevent outbreaks from occurring, then all the evidence suggests we could return the coral cover to its 1985 levels within 20 years.”

Great Barrier Reef damage may yet be repaired

“The coral decline revealed by this study – shocking as it is – has happened before the most severe impacts of ocean warming and acidification associated with climate change have kicked in,” says John Gunn CEO of AIMS. “We can achieve better water quality, we can tackle the challenge of crown of thorns, and we can continue to work to ensure the resilience of the reef to climate change is enhanced.”
Other experts are optimistic that the damage done since the 1980s can be fixed. Professor John Pandolfi, director of the University of Queensland’s Centre for Marine Sciences says that “if we can manage local stressors such as pollution levels and coastal development, then we can get the reef back to a state of health and give it as good a chance as possible of withstanding the onslaught of climate change as it develops.”

Climate change and the world’s reefs

AIMS is now working with the Great Barrier Reef Marine Park Authority (GBRMPA) to determine management responses to the study’s findings. The GBRMPA says it is focused on improving water quality, reducing starfish numbers, and increasing general awareness about threats.

“Our approach is to inform the public about the global issues and to encourage global solutions, but at the same time to act directly on local pressures on the reef,” says chairman Russell Reichelt. “I’m committed to doing whatever it takes to improve the resilience of the system and I think the reef has the capacity to climb out of the terrible hole that it’s fallen into.”

Ove says that a global reduction in carbon dioxide emissions is the long-term key to preventing bleaching and reducing the intensity and volume of storm systems. “What we do in the coming decade will ultimately determine the future of ecosystems like this one,” he adds.

Below: An AIMS video shows crown-of-thorns starfish infesting a part of the Great Barrier Reef.

Great Barrier Reef gest tested for flood damage
Pygmy sea horse and corals found at new depths
What do crocheted corals and maths have in common?
Deep-water corals adapt to low light
3-D maps reveal depths of the ocean floor
Coral spawning: a rare natural wonder
Sea cucumber poo to save Great Barrier Reef
Protecting the Coral Sea
Pygmy seahorse and corals found at new depth
Sawfish uses snout to detect and stab prey
State of our oceans
10-year census finds thousands of marine species
Deepwater corals adapt to low light
What does crochet, coral and maths have in common?
World Heritage sites of Australia
Ningaloo given World Heritage status
Ningaloo revealed
Native fish swims 800km to find a mate
GALLERY: State of our oceans
Bigger fish groups make better decisions
Scientists eavesdrop on fish chatter
10 of the best shipwreck dives around Australia