The National Coral Bleaching Taskforce in Australia has recorded the ‘worst’ bleaching event ever seen on the Great Barrier Reef. During aerial surveys, 95 % of the reefs between Cairns and Papua New Guinea were recorded as severely bleached.
The National Coral Bleaching Taskforce brings together the research efforts of Australia’s marine science and research centers. Ten research institutes and over 300 scientists are involved in research on and monitoring the health of, the Great Barrier Reef. Surveys of the coral reefs are being conducted by air, on research vessels and diving surveys.
Professor Terry Hughes is involved in the aerial surveys being conducted over the entire length of the Great Barrier Reef. Of the 520 reefs they have flown over so far (4000 km worth), only four reefs were seen not to have any bleaching. In an interview with the BBC, he reported that ‘the severity is much greater than in earlier bleaching events in 2002 or 1998′. All types of coral have seen to be affected, including the most hardy ‘massive’ corals. Divers, conducting more detailed environmental surveys have reported up to 50 % mortality of the bleached coral. However, much of the reef has yet to be surveyed in detail, so the extent of damage below the surface coral is not yet truly known. It is also unknown whether the reefs will be able to recover from such extreme bleaching events and ‘it’s still too early to tell just what the overall outcome will be.’ says Prof. Hughes.
Bleaching on the Great Barrier Reef
Coral bleaching occurs when abnormal high water temperatures cause stress to individual corals. The coral then drive out the symbiotic algae called the zooxanthellae. The zooxanthellae are photosynethetic algae that live within the coral and provide the majority of nutrients to the coral. They also provide colour to the corals, so when the zooxanthellae are forced out, the corals are left white. Corals are known to survive bleaching events and zooaxanthellae to return to bleached corals. However, the more severe the bleaching event, the less likely it is for the coral to be recolonised by zooxanthellae and survive. This severe bleaching event currently being observed on the Great Barrier Reef is being blamed on man-made climate change, which has caused a sea surface temperature rise of between 0.5 and 0.8 degrees since the 1880’s. This year, the continuing temperature rise of Australia’s coastal surface waters has been exacerbated by the natural El Nino event this winter.
Healthy, bleached and dead coral (www.gbrmpa.gov.au)
Tropical coral reefs, including the Great Barrier Reef, are also under threat from destructive fishing practices, overfishing, careless tourism, pollution, sedimentation, coral mining, as well as climate change. Last year, Unesco voted to keep the Great Barrier Reef off their Danger list, however many environmentalist want the decision to be reassessed due to the threats facing the world’s larger living structure.
BBC. Australia’s Great Barrier Reef hit by ‘worst’ bleaching [online] Accessed at http://www.bbc.co.uk/news/world-australia-35914009
Arc Centre of Excellence. coral Reef Studies. Coral bleaching taskforce documents most severe bleaching on record [online] Accessed at http://www.coralcoe.org.au/media-releases/coral-bleaching-taskforce-documents-most-severe-bleaching-on-record
NOAA. What is coral bleaching? [online] Accessed at http://oceanservice.noaa.gov/facts/coral_bleach.html
WWF. Coral Reefs: threats [on;ine] Accessed at http://wwf.panda.org/about_our_earth/blue_planet/coasts/coral_reefs/coral_threats/
Hobday A., and Hartog, J. Sea temperatures and climate change [online] Accessed at http://www.redmap.org.au/article/sea-temperatures-and-climate-change/
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