Thaindian News

Sydney, Jan 7 (IANS) Seaweeds have claimed huge tracts of the coastal shelf of Australia’s Great Barrier Reef (GBR) and are endangering them, says a new study.
Part of a global effort to record and understand changes in coral reefs, the study has found that more than 40 percent of inshore reefs on the GBR are dominated by seaweeds (macroalgae).

“The GBR is widely regarded as the world’s most intact large reef system - and that’s the way we aim to keep it,” says Dave Bellwood, professor at the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

Worldwide, many scientists consider that a shift from coral-dominated reefs to weed-dominated ones, signals a rather irreversible decline in coral ecosystem health.

Much, therefore, depends on keeping coral-dominated reefs in as weed-free a condition as possible, Bellwood suggests.

“We carried out two major censuses in the northern and central regions, sampling reefs close to the shore, in the mid-GBR lagoon, and on the outer GBR, in which we swam more than 500, 10-metre transects, taking careful note of the reef composition,” said Bellwood.

Seaweed cover was greatest on inner-shelf reefs - around 43 percent were dominated by weeds - and decreased markedly to around four percent on mid-shelf and outer-shelf reefs in both regions of the GBR.

“In our survey, the corals of the mid-shelf reefs were in much better condition - and one of the things we can clearly do is make sure they stay that way. It would be tragic if macroalgae started to spread on them,” he adds.

Key to this, Bellwood says, is maintaining strong populations of browsing and grazing fishes, like parrot, surgeon, rabbit and bat fish, which keep the weeds down by ‘mowing’ them and preventing them from getting a foothold, says a James Cook release.