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Worst coral reef die-off in 11,000 years

Worst coral reef die-off in 11,000 years

Worst coral reef die-off in 11,000 years
December 18, 2006

Two new studies by scientists at the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University suggest that coral reefs may be in worse shape than previously thought. The first, appearing in the journal Geology indicates that the current large scale coral die-offs are now occurring more frequently than at any time in the last 11,000 years. The second, published in Current Biology, suggests that the loss of a single “keystone” species can trigger a rapid shift in the health of a reef.

The first study, led by Associate Professor John Pandolfi of the Australian Research Council Centre of Excellence in Coral Reef Studies and The University of Queensland, examined fossilized reefs of the Huon Peninsula in Papua New Guinea and determined that past reef die-offs occurred about every 1500 years due to some catastrophic event — a rate that is exceeded by the current decline in coral reefs;

“The cause of some of these events was volcanic, but others may have been due to bleaching, disease, or something else – we just don’t know. Regardless, what is clear is that the frequency of die-off was so much lower than it is today. The frequency of reef events in the fossils is at least an order of magnitude less than it is today” said Pandolfi.

Pandolfi said the results show that the ancient reefs “recovered rapidly after these events, taking as little as 100 years to be repopulated by the corals that normally occurred there.”

“The recovery of the Great Barrier Reef from the devastating impact of the crown of thorns starfish took less than a few decades, at least in part due to comprehensive reef management,” Pandolfi continued,”…but this rate of recovery isn’t seen in other parts of the world….some reefs still haven’t recovered from [events in the last century].”

Pandolfi said that he hopes his ongoing research will help reef managers better understand what they need to do to help current reefs bounce back from impact events.

Single species found to be crucial to reef recovery

One area the needs further exploration is the role of individual species in coral reef ecology. The Current Biology did just this and determined that reefs may be more fragile than previously thought.

Using experimental plots on the Great Barrier Reef to simulate overfishing, David R. Bellwood, Terry P. Hughes, and Andrew S. Hoey found that a single species plays a key role in reef recovery. Loss of this species could leave reefs more susceptible to damage from algae.

In the experimental plots, the researchers “intentionally triggered a phase shift to algal dominance on a healthy reef” and then “filmed the reef’s recovery with remote underwater digital videos cameras.” They found that “only two of the 27 herbivorous fish species present on the reefs had any significant impact on its recovery from algal overgrowth.” Surprisingly, the dominant browser was a rare batfish, Platax pinnatus, species previously unknown as an algae eater. “Meanwhile,” reported a statement from Cell Press, publisher of Current Biology, “parrotfishes and surgeonfishes, which are the routine consumers of seaweed on coral reefs, were unable to reverse runaway algal blooms.”

The research demonstrates the importance of a single rare species in the recovery of coral reefs and suggests that the loss of this keystone species could undermine the regenerative capacity of coral reef ecosystems.

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