Rabbits to the rescue of the reef

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 placed 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.