Science for sustainable reefs
Box 2 | The Great Barrier Reef MPAs: how effective are they?
It’s widely thought that networks of marine protected areas (MPAs) can play a large role in protecting and sustaining coral reef systems. There is evidence to support this, but to be effective the size and spacing of MPAs need to be carefully considered, particularly if they are to provide protection against threats associated with climate change.
In 2004 a third of the Great Barrier Reef was placed off limits to fishing to form the then world’s largest network of MPAs. Australian researchers have been studying what this has meant for certain fish stocks. They found that after only 1.5 to 2 years coral trout numbers rebounded by 31-75 per cent on a majority of reefs which had been closed to fishing. The researchers were amazed at the speed at which coral trout populations recovered – and also the sheer scale and consistency of the response. However, densities of coral trout on the reefs left open to fishers showed little or no change. In time, the higher fish populations on closed reefs may lead to improvements in fish numbers on open reefs, as juveniles from closed areas settle on open ones.
Recent research by marine biologists shows that even small reef fish, like baby clownfish, can travel as far as 35 kilometres between reefs. MPA networks can help sustain resident fish populations both by local replenishment and by fish larvae coming in from other neighbouring reserves. But networks of MPAs need to be quite large with individual reserves quite close to other reserves if they are to make a difference in the face of large regional disturbances like mass bleaching events. A survey of 66 sites in the Indian Ocean following a major coral die-off in 1998 showed that existing no-take areas may not be much help in enabling reefs to recover from major coral bleaching events. Many of these no-take areas were set up in the late 1960s and early 1970s to protect fish, before climate change and its impact on corals became a major issue. Several are small, and are surrounded by areas which are heavily fished or otherwise exploited. The researchers recommended that these existing zones should not be removed, but that new areas need to be added to them.
A major disturbance like bleaching can affect a huge area of the reef. If you have extensive and close reserve systems, then the chances are much higher they will contain organisms that escape bleaching which can help to recharge the reef as a whole.
How do green zones on the Great Barrier Reef work? (web seminar, Australian Research Council Centre of Excellence for Coral Reef Studies)
Nemo come home (web seminar, Australian Research Council Centre of Excellence for Coral Reef Studies)
Protected fish stage a comeba (Australian Research Council Centre of Excellence for Coral Reef Studies)
The marine protected area (Stanford University, USA)
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Posted September 2009