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. At a briefing to parliamentarians in Canberra, they said protected areas were rebuilding fish populations in some parts of the Great Barrier Reef.
Warming seas are likely to affect the reef severely within a few decades. Pollution is also a growing problem, particularly fertilisers that wash from agricultural land into water around the reef, stimulating the growth of plants that stifle the coral. The assembled experts told parliamentarians that fish able to graze on invading plants played a vital role in the health of reef ecosystems.
“The Great Barrier Reef is still a resilient system… and herbivorous fish play a critical role in that regenerative capacity, by keeping the dead coral space free of algae, so that new juvenile coral can re-establish themselves,” said Professor Terry Hughes from James Cook University in Townsville. 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. “So managing fisheries can help to maintain the reef’s resilience to future climate change,” he said. In recent years, Marine Protected Areas have been set up along the Great Barrier Reef in order to provide sanctuaries where fish and other marine creatures can grow and develop.