SYDNEY - Scientists studying reefs off Australia said on Thursday sharks play a fundamental role in the health of coral, and overfishing of them made reefs more vulnerable to global warming and weather disasters.
A research team, led by Mark Meekan from the Australian Institute of Marine Science (AIMS), studied the impact of sharks at the Rowley Shoals and Scott Reefs 300 kilometres (185 miles) off northwest Australia over 10 years.
"Where shark numbers are reduced we see a fundamental change in the structure of food chains on reefs," said Meekan.
"We see increasing numbers of mid-level predators such as snappers, and a reduction in the numbers of herbivores such as parrot fishes.
"The parrot fishes are very important because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances."
When coral dies algae grows over it, compromising its ability to regrow.
Meekan said the herbivorous fishes chewed out small spaces so regrowth could take place.
The study compared the impact of cyclones and bleaching events on the marine-protected Rowley Shoals, where fishing is banned, with the neighbouring Scott Reefs, where Indonesian fishermen - mostly from West Timor - are allowed to catch sharks.
It found less coral and more algae on the fished reefs after a major disturbance, which Meekan said was significant as the pressures of global warming increased.