Weed-eating fish ‘vital to coral reefs’ survival’

March 11th, 2011 - 12:50 pm ICT by ANI  

Washington, Mar 11 (ANI): A new study has found that a weed-eating fish could be the key to saving the world’s coral reefs.

Researchers at the ARC Centre of Excellence for Coral Reef Studies has found weed-eaters like parrotfish and surgeonfish can only keep coral reefs clear of weed up to a point. After the weeds reach a certain density, they take over entirely and the coral is lost.

Dr Andrew Hoey and Professor David Bellwood at CoECRS and James Cook University found that once the weeds reach a certain density, the fish no longer control them, and prefer to graze less weedy areas.

“As a result, the whole system tips from being coral-dominated to weed-dominated,” Andrew said.

“And our work shows that it doesn’t take a very high density of the fleshy seaweeds like Sargassum to discourage the fish, a patch of weed the size of a back garden could be enough to trigger a change. The fishes show a clear preference for grazing more open areas.”

“In countries where people harvest the weed-eating fishes with spearguns, nets and so on, like Fiji, we are seeing a fundamental change in the nature of reefs from coral to weeds,” Andrew said.

The team transplanted different densities of sargassum weed on a reef off Orpheus Island - and then used remote video cameras to record what the fish did.

In all they counted 28 species of fish taking 70,685 separate bites of weed and removing an average of 10 kilos of weed a day. In the more open areas this was enough to control the weed.

But Andrew also noticed the fish avoided the densely-weeded areas, perhaps for fear of predators.

“This suggested to us there is a critical weed density, beyond which fish no longer control the weeds and they then take over the reef system. This in turn implies a need to keep the herbivore population as healthy as possible to avoid the reef reaching that tipping point.”

“We should also bear in mind that this study was conducted in an area of the Great Barrier Reef Marine Park that has been protected from all commercial and recreational fishing for over 20 years and so is likely to have intact fish communities.

“How herbivores respond in areas of the world where they are still heavily fished may be absolutely critical to the survival of large areas of reef in Asia and the Pacific - and hence to the human communities who depend on them for food, tourism and other resources.”

The paper appears in the latest issue of Ecology Letters. (ANI)

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