A Blue Starfish (Linckia laevigata) resting on hard Acropora and Porites corals (one can also see Anthiinae fish and crinoids). Lighthouse, Ribbon Reefs, Great Barrier Reef. Photo: Wikipedia
Widespread coral bleaching resulting in decline and habitat loss has hit the Great Barrier Reef over the past two years, according to the Australian authorities.
Estimated 29% of shallow water corals in the Great Barrier Reef died from bleaching in 2016.
Estimated 70% of shallow water corals died in the northern part of the Reef.
Further coral cover decline is expected in 2017 as cyclone Debbie has also impacted the Great Barrier Reef.
In addition to harming biodiversity, coral bleaching, which is mostly caused by rising water temperatures related to global warming, will have a major economic impact on Australia’s Queensland.
The Great Barrier Reef off Australia‘s west coast has suffered widespread coral decline and habitat loss even more than expected over the past two years, according to the Australian authorities.
Coral bleaching occurs when as a result of warmer water temperatures likely related to global warming corals expel the algae living in their tissues, and turn completely white.
Even though bleaching in itself does not kill corals, as the algae provides 90% of their energy, its expulsion causes them to starve and become subject to mortality.
The Great Barrier Reef is the world’s largest coral reef system consisting of over 2,900 individual reefs and 900 islands spanning over 2,300 km (1,400 miles) in the Coral Sea, off the coast of the Australian state of Queensland.
The reef, which has a combined territory of 344,000 sq. km (133,000 sq. miles), is a UNESCO World Heritage Site.
‘Widespread Coral Decline’
Over the past two years, global coral bleaching caused widespread coral decline and habitat loss on the Great Barrier Reef, announces the Great Barrier Reef Marine Park Authority (GBRMPA), an institution of the Australian government.
Throughout 2016 the Marine Park Authority, Queensland Parks and Wildlife Service, the Australian Institute of Marine Science (AIMS) and the ARC Center of Excellence for Coral Reef Studies conducted extensive surveys of the mass bleaching, the GBRMPA said.
It pointed out that aerial and in-water surveys confirmed a pronounced gradation in impacts from north to south.
The most severe mortality was confined to the area north of Port Douglas, where an estimated 70% of shallow water corals died and there was significant variability between and within reefs.
An estimated 29% of shallow water corals in the Great Barrier Reef died from bleaching in 2016.
Coral bleaching did extend to deeper corals beyond depths divers typically survey to, but mortality cannot be systematically assessed.
This up from the original estimated 22% in mid-2016, with most mortality occurring in the north of the Reef.
Over this same period there continued to be strong recovery in the south in the absence of bleaching and other impacts, the Great Barrier Reef Authoritiy said.
Great Barrier Reef Marine Park Authority Chairman Russell Reichelt said ongoing and future climate impacts were concerning.
“As has been the case with reefs across the world, the Great Barrier Reef has experienced significant and widespread impacts over the last two years," he says.
“We’re very concerned about what this means for the Great Barrier Reef itself and what it means for the communities and industries that depend on it,“ Reichelt adds.
“The amount of coral that died from bleaching in 2016 is up from our original estimates and, at this stage, although reports are still being finalized, it’s expected we’ll also see an overall further coral cover decline by the end of 2017,“ he elaborates.
The Great Barrier Reef Authority added that in 2017, further coral loss was expected from the second consecutive year of bleaching and the impacts of tropical cyclone Debbie.
This is in addition to ongoing impacts from crown-of-thorns starfish, coral disease and poor water quality from coastal run-off.
“The 2017 pattern of bleaching was similar to 2016, but most severe in the center of the Reef between Cairns and Townsville. Ongoing thermal stress is also causing elevated coral disease,“ the Authority explains.
It noted that tropical cyclone Debbie impacted around a quarter of the Great Barrier Reef in early 2017.
According to the Australian institution, impacts from cyclones are generally patchy, but due to its category four intensity and slow speed as Debbie crossed the Great Barrier Reef, coral mortality is expected to be high in this zone, which includes the Whitsunday Islands tourism area.
A complete picture for 2017 will not be available until early next year. Ongoing bleaching, tropical cyclone Debbie, crown-of-thorns starfish and coral disease are all having impacts.
The Australian Institute of Marine Science (AIMS) has been tracking coral cover in the Great Barrier Reef since 1985, providing a holistic picture over time of net coral cover (including both coral loss from impacts and coral growth from recovery).
While varying from year-to-year, the AIMS data shows a declining trend in coral cover since 1985.
Cyclones and coral-eating crown-of-thorns starfish were responsible for the greatest coral loss before 2016.
“Combined with coral bleaching — which is predicted to become more frequent and more severe as a result of steadily rising ocean temperature — the long-term trend of coral decline is expected to continue and accelerate," the Great Barrier Reef Marine Park Authority forecasts.
In April 2017, the Australian Council released a report that found bleaching could reduce the number of visitors to Queensland by 1 million per year, and a loss of AUD 1 billion (USD 745 million) in tourism revenue.
“Over the next two to three decades, bleaching events are likely to become even more frequent and severe in Australia, with catastrophic impacts on reef health and the economy," a Council report says.
In July 2017, the UNESCO World Heritage organization is going to decide on whether to list the Great Barrier Reef as being a World Heritage Site “in danger", a possibility which has caused grave concern with the Australian government.