Seeking the keys to coral reef renewal & recovery
08 September 2011
VITAL CLUES to coral reef recovery have been identified in a remarkable research project in which three scientists laboured to hand-build 30 coral reefs in Papua New Guinea from hundreds of tonnes of rock and gravel.
Working in a shallow, sandy area of Kimbe Bay, the team constructed the artificial reefs over several weeks, with just a boat and their bare hands, to find out whether it is possible to rescue a damaged coral reef from obliteration and restore its richness.
“When a reef suffers a heavy impact— such as a storm or outbreak of coral bleaching—there are two different effects on the coral habitat,” said Dr Mary Bonin of the Centre of Excellence for Coral Reef Studies and James Cook University.
“First, a lot of the habitat that was once available to fish is totally lost. And second, the habitat that still remains is often fragmented, or broken up into smaller patches.
“We wanted to figure out if the increased habitat patchiness is actually a problem for coral reef fishes, or whether it is really the loss of habitat that causes fish to decline following an impact.”
Together with Professor Geoff Jones and Dr Glenn Almany, Dr Bonin set out to construct 30 real-life coral reefs in an open sandy area where there were no natural reefs nearby.
Each ‘reef’ was constructed from boulders and coral debris, carted manually from the shore in a 6 metre boat, crowned with a square metre of living bottlebrush coral and stocked with 20 small blue and yellow damselfish [pictured]. After a time the ‘reef’ acquired richer diversity, as baby fish came in on the current and settled.
The scientists then simulated the effects of habitat loss – the sort of colossal damage that reefs suffer during a bad bleaching event or cyclone – habitat fragmentation, where the existing reef is broken into smaller fragments, and a combination of the two.
“We think this is because a fragmented or patchy habitat reduces the competition between fishes, creating more room for the weaker ones or for newcomers to settle. When the habitat is just a single patch, the tough guys will tend to dominate the whole area and drive the others away.”
The researchers’ finding challenges a widely-held view that habitat fragmentation always leads to a dramatic loss of fish numbers and diversity.
“Habitat fragmentation has had a bad wrap,” Dr Bonin said. “Our findings suggest that it is actually habitat loss that is the major problem for coral reef fishes following an impact.
“It is certainly the case that in the small areas we created and studied, you get a positive effect on fish numbers and diversity from habitat fragmentation - whereas habitat loss of 75% or more is a disaster.”
Because fragmentation can bring greater diversity, there may be things which reef managers can do to restore badly-damaged coral communities by mimicking its effects.
“The fact that habitat patchiness can have a positive effect on fish diversity is really exciting because it means that even if it isn’t possible for managers to restore an entire coral reef, it will still be highly beneficial to restore small patches of habitat” says Dr Bonin.
“We now want to investigate what happens over much larger areas, and examine how the degree of isolation of the remaining habitat fragments influences species’ responses to a disturbance.”
Source: James Cook University, 5 September
http://www-public.jcu.edu.au/news/current/JCU_086231
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