Scientists: Sea Rabbits May Save The Great Barrier Reef; 'Came Out Of Nowhere'

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Scientists: Sea Rabbits May Save The Great Barrier Reef; 'Came Out Of Nowhere'
TOWNSVILLE, Australia -- While rabbits continue to ravage Australia's native landscapes, rabbit fish may help save large areas of the Great Barrier Reef from destruction.
The reason, say scientists, is the same in both cases - both rabbits and rabbit fish are efficient herbivores, capable of stripping an area of vegetation. However, in the case of the Reef, it is the vegetation that is the problem - and the rabbit fish, the answer.
"When a coral reef is weakened or damaged through human activity such as climate change or pollution or by a natural disaster like a cyclone, the coral will usually recover provided it is not choked by fast-growing marine algae," explains Professor David Bellwood of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
"The problem is that over the years we have fished down the populations of fish that normally feed on the young weed to such a degree that the weed is no longer kept in check, it can now smother the young corals and take over. This is called a phase-shift, and the chances of corals re-establishing afterwards are usually poor. If the weed takes over, you've lost your reef." Prof. Bellwood and fellow researcher Rebecca Fox have spent recent years running live experiments to see what happens when a reef turns to weed - and which fish, if any, are of help in restoring the coral. "To our surprise and disappointment, the fish that usually 'mow' the reef - parrot fishes and surgeon fish - were of little help when it came to suppressing well established weedy growth. Most herbivores simply avoided the big weeds. "Then, to our even greater surprise a fish we had never seen in this area before was observed grazing on the weed. The rabbit fish (Siganus canaliculatus), came out of nowhere and began to clear-fell the weed on the reef crest."
The rabbit fish were caught on underwater videocams, in schools of up to 15 fish, grazing the crest, slopes and outer flats of the reef, and chomping away at more than ten times the rate of other weed-eaters. "The rabbit fish is not a fish you tend to take a lot of notice of," Prof. Bellwood explains. "Like its terrestrial counterpart, it is brown, bland and easily overlooked - but it could be very important when it comes to protecting the GBR."
"We hadn't seen it previously at this site despite conducting over 100 visual censuses. This made its appearance in numbers sufficient to check the weedy growth all the more remarkable." However the team noticed the rabbit fish concentrated their weed-removal efforts on the crest of the reef and were less effective on the slopes and flats - a feeding preference that is yet to be explained. In a previous study, an overgrown reef had been cleaned up by another unexpected intruder, a striped batfish. Ms. Fox explained that the recovery of damaged reefs may depend on several different 'guilds' of fishes, with different feeding preferences, that will focus on particular parts of the reef and stages of the weed infestation. For such an approach to work, however, all the various species have to be kept intact in the reef environment, ready to play their part in a salvage operation when it becomes necessary. "In Australia these herbivore fish populations are still in fairly good shape, but around the world as the big predators are fished out, local fishermen are targetting the herbivores. In Hawaii, the Caribbean, Indonesia, Micronesia and French Polynesia there are reports of serious declines in herbivore numbers of up to 90 per cent.
"By killing them, we may be unwittingly eliminating the very thing which enables coral reefs to bounce back from the sort of shocks which human activity exposes them to."
Prof. Bellwood says that one of the lessons from the video study is that obscure fish species may play a critical role in the survival and maintenance of coral ecosystems, and should not be overlooked. They are a key part of the resilience of the whole reef system.
"On land the rabbit is a major headache, but in the sea the rabbit fish may be an important factor in helping to keep the world's number one tourist attraction in good shape," he says.

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now if only other areas pay attention

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Doom And Boom: Scientists Astonished By Great Barrier Reef's Recovery From 2006 Bleaching Event
QUEENSLAND, Australia -- Marine scientists say they are astonished at the spectacular recovery of certain coral reefs in Australia's Great Barrier Reef Marine Park from a devastating coral bleaching event in 2006. That year high sea temperatures caused massive and severe coral bleaching in the Keppel Islands, in the southern part of the Great Barrier Reef. The damaged reefs were quickly smothered by a single species of seaweed – an event that can spell the total loss of the corals. However, a lucky combination of rare circumstances meant the reefs were able to achieve a spectacular recovery, with abundant corals re-established in a single year, said Dr Guillermo Diaz-Pulido, from the Centre for Marine Studies at The University of Queensland and the ARC Centre of Excellence for Coral Reef Studies (CoECRS). Dr Diaz-Pulido said that the rapid recovery was due to an exceptional combination of previously-underestimated ecological mechanisms.
"Three factors were critical," he said. "The first was exceptionally high regrowth of fragments of surviving coral tissue. The second was an unusual seasonal dieback in the seaweeds, and the third was the presence of a highly competitive coral species, which was able to outgrow the seaweed. "But this also all happened in the context of a well-protected marine area and moderately good water quality. "It is rare to see reports of reefs that bounce back from mass coral bleaching or other human impacts in less than a decade or two. "The exceptional aspect was that corals recovered by rapidly regrowing from surviving tissue," said Dr Sophie Dove, also from CoECRS and The University of Queensland.
"Recovery of corals is usually thought to depend on sexual reproduction and the settlement and growth of new corals arriving from other reefs," she said. "This study demonstrates that for fast-growing coral species asexual reproduction is a vital component of reef resilience." Professor Ove Hoegh-Guldberg of the CoECRS and The University of Queensland said that coral reefs globally were increasingly being damaged by mass bleaching and climate change. Their capacity to recovery from that damage was critical to their future, he said. "Our study suggests that managing local stresses that affect reefs, such as overfishing and declining water quality, can have a big influence on the trajectory of reefs under rapid global change," Professor Hoegh-Guldberg said. "Clearly, we need to urgently deal with the problem of rising carbon dioxide in the atmosphere, but managing reefs to reduce the impact of local factors can buy important time while we do this." Understanding the different mechanisms of resilience is critical for reef management under climate change.
"Diversity in processes may well be critical to the overall resilience and persistence of coral reef ecosystems globally," said Dr Laurence McCook, from the Great Barrier Reef Marine Park Authority. The research was partially funded by a Pew Fellowship in Marine Conservation awarded to Dr McCook, the Great Barrier Reef Marine Park Authority as well as the ARC Centre of Excellence program. "This combination of circumstances provided a lucky escape for the coral reefs in Keppel Islands, but is also a clear warning for the Great Barrier Reef," Dr McCook said. "As climate change and other human impacts intensify, we need to do everything we possibly can to protect the resilience of coral reefs." The research was published this week in the paper “Doom and boom on a resilient reef: Climate change, algal overgrowth and coral recovery”, in the journal PLoS ONE, by Guillermo Diaz-Pulido, Laurence J. McCook, Sophie Dove, Ray Berkelmans, George Roff, David I. Kline, Scarla Weeks, Richard D. Evans, David H. Williamson and Ove Hoegh-Guldberg.