Marine reserves do more good than expected
Caribbean reefs protected by no-fishing zones despite rise in predators.
A no-fishing zone in the Caribbean appears to be helping both the big fish it was designed to save and, surprisingly, the coral that underlies the ecosystem. That's despite the fact that the large fish chow down on smaller fish that help out the coral.
The study highlights how difficult it can be to predict how an ecosystem responds to changes, the researchers say. But it also reconfirms that protecting biodiversity is a good defense against destructive changes, they add.
The Caribbean coral reefs in question were dealt a blow in the mid 1980s when a mysterious disease almost completely wiped out the spiny urchin (Diadema antillarum). One way these urchins influenced the ecosystem was by grazing down the large alage that grows in the area, making a clear area where juvenile coral could gain an easy foothold. With the urchins gone, it was up to another grazer, the colourful parrotfish, to keep the algae under control.
Parrotfish are hunted and eaten by the predatory Nassau grouper (Epinephelus striatus), another fish in the region. Groupers are often kept in check by fishermen. But some regions in the Caribbean, such as the Exuma Cays Land and Sea Park, are protected from fishing. So Peter Mumby of the University of Exeter worried about how the corals would fare with a mass of groupers around to gobble up all the parrotfish. Perhaps, they feared, the corals would simply be smothered under a blanket of algae.
Fish eat fish world
After five years of diving trips, wherebye Mumby and his international team scuba-dived transect after transect of Caribbean ocean, the group is pleased to report in this week's Science that the corals are faring well1.
Although some small species of parrotfish do get nibbled on a bit more, they found, the large species-just too big to comfortably fit into the mouths of the grouper-have also benefited from the absence of fishermen. These larger parrotfish are fantastic grazers, making the algae cover fourfold less inside the park than outside the reserve.
"It is good to know that the use of reserves to manage fish and corals is compatible," says Mumby. But he adds that there could be more complicated interactions elsewhere, and that the corals may need additional help. "I don't feel that marine reserves are the only tool necessary to manage reefs," he says.
Robert Carpenter, a marine biologist at California State University, Northridge, California, says the result is good news. In his own work, he has documented the gradual re-emergence of the urchin and its positive benefit for corals. Carpenter says he looks forward to the day when both urchins and parrotfish share the task of clearing way for baby coral. "The benefit of biodiversity is that it gives us redundant players in the system, which can then provide resilience in the face of disturbance," he says.
- Mumby P., et al. Science, 311. 98 - 101 (2006).