A comprehensive study supported by the Australian Institute of Marine Science and the National Environmental Research Program of the Australian Government and published online, October 1, 2012, in Proceedings of the National Academy of Sciences of the United States of America concludes that Australia’s Great Barrier Reef has lost half of its coral cover since 1985. The Great Barrier Reef is the world’s largest coral reef ecosystem and includes 2,900 individual reefs within an area of about 133,000 square miles. It is also one of the best protected marine areas in the world, with a third of the Great Barrier Reef marine park off-limits for fishing and collecting – making the findings all the more alarming.

According to the article, “There is increasing concern about the progressive degradation of the world’s coral reefs. Major anthropogenic risk factors include mortality and reduced growth of the reef-building corals due to their high sensitivity to rising seawater temperatures, ocean acidification, water pollution from terrestrial runoff and dredging, destructive fishing, overfishing, and coastal development.” In the case of The Great Barrier Reef, the study points out that three factors are overwhelmingly responsible for this loss of coral cover: intense tropical cyclones which have caused massive damage, primarily to reefs in the central and southern parts of the Reef; population explosions of the coral-consuming crown-of-thorns starfish which have affected coral populations along the length of the Reef; and two severe coral bleaching events which have also had major detrimental impacts in northern and central parts of the Reef.

Abstract: The world’s coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef. Based on the world’s most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985–2012), we show a major decline in coral cover from 28.0% to 13.8% (0.53%y−1), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%, and 10%of the respective estimated losses, amounting to 3.38% y−1 mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85%y−1, demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y−1, despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef. Such strategies can, however, only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase.

Image 1 for article titled "The Great Barrier Reef Has Lost Half Its Coral Cover Since 1985"
Acanthaster planci, commonly known as the crown-of-thorns starfish, is a large multi-armed starfish (or seastar) that usually preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns receives its name from poisonous thorn-like spines that cover its upper surface. It is the second largest sea star in the world. They are usually of subdued colors, pale brown to grey-green, but they may be more brightly colored in some parts of their wide distribution (Wikipedia: Crown-of-thorns starfish)

Image 2 for article titled "The Great Barrier Reef Has Lost Half Its Coral Cover Since 1985"
Two images showing the relationship of water temperature to coral bleaching along the Great Barrier Reef. Warm pink and yellow tones show where sea surface temperatures were warm in the top image. The warmest waters are the shallow waters over the reef near the coast, where coral bleaching was most severe in the summer. The lower image shows chlorophyll concentrations, where high concentrations (yellow) generally point to a high concentration of phytoplankton in surface waters of the ocean. In this image, the bright yellow dots actually represent the coral reefs, and not surface phytoplankton. Dated February 2006; Wikipedia: Great Barrier Reef