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Global Ideas

Corals at the mercy of storms and starfish

According to a new study, Australia has lost half its coral reefs. But the main cause of the damage is not climate change, but storms and a starfish.

The corals of the Great Barrier Reef, east of Australia, are dying in alarming numbers. A recent study by scientists at the University of Wollongong in New South Wales published in the Proceedings of the National Academy of Sciences shows just how seriously they are being affected. According to the study, over the past 27 years, around half of all Australian corals have perished.

It's been known for some time that the reefs are under threat, but the study showed that the danger comes from somewhere unexpected: the main damage is not done by the gradual heating up of the ocean and its acidification as a result of climate change. Instead, the main damage is being done by storms and a thorny sea creature which reproduces particularly aggressively: acanthaster planci, more commonly know as the crown-of-thorns starfish.

The starfish literally devours the corals, and its numbers have increased drastically as a result of the high level of nutrients in the water - levels that have risen particularly during the past decades, particularly due to the use of fertilizers in farming.

Fertilizers feed the foes

The crown-of-thorns starfish has become the number one enemy of the corals: Australian scientists attribute around half the total losses to them. Over 33 percent is caused by storms which cause physical damage to the reefs. And then, in third position, comes climate change and acidification of the oceans, whereby a chemical reaction takes place in which carbon dioxide and water form carbonic acid. Carbonic acid is responsible for so-called coral bleaching, which is responsible for around 18 percent of the coral losses. This process was particularly severe in 1998 and 2002.

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An intact coral reef can host a plethora of other creatures.

But the dying of the corals isn't irreversible: John Gunn, head of the Australian Institute for Marine Science (AIMS), estimates that the corals could bounce back over the course of several decades, if waste water - rich in nutrients for the starfish - were no longer allowed to run off into the ocean.

The world through the eyes of corals

The threats and the opportunities as seen through the "eyes" of corals can now be explored online, too: "Namati's World - dreams and fears of a young coral in the South Pacific" is a new DW web-documentary. Set in the underwater world just off the island of Pele, in the Pacific state of Vanuatu, it allows young audiences to learn interactively about the threats to corals from fertilizer and acidification.

Scientists warn that without intervention, the coral cover of the reefs will drop to between 5 and 10 percent within the next 10 years. For their latest study, AIMS says they have data from more than 200 individual reefs of the Queensland coast, covering the period 1985-2012.

Even if it were just possible to stop the damage being done by the crown-of-thorns starfish, they say, coral cover could increase again by 1 percent a year.

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