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solonavi 20 March 2008 Coral Reefs, Global Warming 322 views No Comment Print This Post  Email This Post

BBC

A healthy fish population could be the key to ensuring coral reefs survive the impacts of climate change, pollution, overfishing and other threats.

Australian scientists found that some fish act as “lawnmowers”, keeping coral free of kelp and unwanted algae.

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The assembled experts told parliamentarians that fish able to graze on invading plants played a vital role in the health of reef ecosystems.

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His research group has conducted experiments which involved building cages to keep fish away from sections of reef.

They found that three times as much new coral developed in areas where the fish were present as in the caged portions.

Parrotfish in particular use their serrated jaws to scrape off incipient algae and plants.

More recently, his team has also identified the rabbit fish – a brown, bland-looking species – as a potentially important harvester of seaweed.

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Dr Peter Doherty from the Australian Institute of Marine Science presented data showing that just two years of protection brought significant increases in populations of important species such as coral trout and tropical snapper.

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The eggs, he showed, travelled well outside the boundaries of the protected zones, potentially increasing fish populations in non-protected areas too.

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Professor Ove Hoegh-Guldberg from the University of Queensland noted that unusually warm water in 1998 and 2002 had bleached and damaged coral in southern parts of the Barrier Reef.

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In the past, he said, bleaching events happened only at the warm extremes of natural cycles such as El Nino; but now the overall water temperature is higher, which makes the peaks of the cycles more harmful to coral.

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At high temperatures, coral polyps expel the algae which normally live with them in a symbiotic relationship, turning the reef white. The algae typically provide most of the polyp’s nutrition; without them, the polyps eventually die.

Even if a bleached zone contains live polyps and carries the potential to recover when waters cool, a quick invasion of kelp, or types of algae that do not live symbiotically with coral, can make the die-off permanent – hence the protective role of plant-munchng fish.

The parrotfish performs a vital role as a “lawnmower” of the reef