How marine reserves are giving coral reefs a helping hand

It may be no surprise that marine reserves protect the fish that live in them, but now scientists from the University of Exeter have shown for the first time that they could also help improve the health of coral reefs.

In a paper in the prestigious journal Science, Dr Peter Mumby and colleagues looked at how a marine park in the Bahamas was affected by the return of the reef’s top predator, the Nassau Grouper. Researchers were concerned that an increase in groupers could have an adverse effect, because they feed on parrotfish which play a vital role in maintaining the reef ecosystem.

Dr Peter Mumby, from the School of Biosciences at the University of Exeter, said: “While an increasing number of larger predators is essentially good news we had concerns that this might result in a decrease in the numbers of parrotfish, which could ultimately damage the health of the reef. More than 20 years ago sea urchins in the Caribbean were wiped out by disease, leaving parrotfish as the main grazer of reef surfaces. The fish use their teeth to remove seaweed from the reef which allows new corals to settle and grow.This grazing process is essential to the health of the system.”

“Caribbean reefs are still trying to recover from the devastating effects of an El Nino bleaching event in 1998 which caused widespread damage to coral around the world.

What we have found is that marine reserves might provide exactly the right conditions to allow this to happen. Interestingly, once parrotfish reach a length of around 28 cm, they become too big for even the largest grouper to swallow. This ’escape’ from a risk of predation means that most reserves are unlikely to reduce the amount of grazing even after the number of predators rises.”

Peter added, “Diving in the Exuma Cays Land and Sea Park was fun because a large number of sharks turned up to watch us work. Sharks have been heavily fished on most coral reefs so it’s always a thrill to visit one of their sanctuaries.”