Sharks are vital for the health of coral reefs, a model of the food web in a reef suggests.
According to the model, created by Enric Sala of the Scripps Institution of Oceanography in San Diego, California, and colleagues, the removal of top predators allows lesser predators such as groupers to thrive, leading to a reduction in the number of algal feeders such as panrotfish. That makes reefs more vulnerable to disturbances that kill corals, such as disease, pollution and global warming (Proceedings of the National Academy of Sciences, vol 102, p 5443).
The study suggests that the loss of sharks may have contributed to the decline of reefs in the Caribbean, most of which are now dominated by algae. But proving the theory will be difficult, Sala says. "We don't have a reef where the only thing missing is the sharks." A few decades ago there was extensive overfishing of all species in the Caribbean, including algae grazers. This was followed in 1982 by a disease that wiped out sea urchins, allowing algae to take over.
The presence of sharks could be important for the recovery of the reefs, Sala says. "Top predators are very important for maintaining the stability of the system." To protect sharks, large marine reserves that encompass their entire range must be established, he says.
From issue 2496 of New Scientist magazine, 23 April 2005, page 21