Australia's Great Barrier Reef is in trouble. According to a new study, the amount of coral cover in the reef has dropped by 50.7% in the past 27 years. It's down to half the size it was in 1985.
The Great Barrier Reef is the largest coral reef system in the world and is visible from outer space. It is composed of nearly 3,000 individual reefs, built by billions of tiny animals known as coral polyps. The reef is home to more than 400 different types of coral, as well as fish, turtles, molluscs, rays, dolphins, sponges, and many other marine organisms.
The new analysis is based on data gathered from more than 2,000 surveys of 214 reefs from 1982-2012. The team of Australian researchers was able to break down the cause of the decline into three major factors: storm damage from tropical cyclones (48%), bleaching (10%), and predation by crown of thorns starfish (42%).
Tropical storms cannot be stopped, and ocean warming (the primary cause of coral bleaching) is an effect of global climate change, which does not give any indication of lessening soon. But the impact of the crown of thorns starfish can be mitigated.
The crown of thorns starfish is a large starfish (10-14 in.), found throughout the Pacific Ocean, that preys specifically on coral polyps. Its name comes from the venomous thorn-like spines covering its upper surface. Its numbers have shot up in the last few decades — possibly due to a decline in its predators — and now it's wreaking havoc on coral reefs.
Right now, the Great Barrier Reef's coral is declining at a rate of 3.38% per year. The researchers estimated that without the effects of storms, bleaching, and the crown of thorns starfish, the coral would grow at a rate of 2.85% a year. But if only the starfish were controlled, coral cover would increase at 0.89% a year. It's not a lot, but it demonstrates the capacity for recovery.
The researchers suggest developing control measures for reducing crown of thorns starfish populations, but caution that these will only be successful if global warming is also addressed. If climate change continues, tropical storms and bleaching will only increase, and further coral decline will be inevitable.
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The 27—year decline of coral cover on the Great Barrier Reef and its causes