Lack of Sharks Puts Coral Reefs at Risk

Declining shark populations are detrimental to coral reefs in Australia, according to a new study which will appear in the upcoming edition of the journal PLOS One.

Johnathan Ruppert, a researcher on a team that engaged in long-term monitoring of coral reefs of the northwestern coast of Australia, said that in locations where shark numbers are reduced due to commercial fishing, there is also a decrease in the herbivorous fishes that play a vital role in promoting reef health.

Mark Meekan, the research team leader from the Australian Institute of Marine Science, said at first the study results might seem strange.

"However our analysis suggests that where shark numbers are reduced, we see a fundamental change in the structure of food chains on reefs," Meekan said.

"We saw increasing numbers of mid-level predators -- such as snappers -- and a reduction in the number of herbivores such as parrotfishes," said Meekan. "The parrotfishes are very important to coral reef health because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances."

The study comes at a time when coral reefs are facing numerous pressures from direct human activity -- such as overfishing -- and indirect phenomena such as climate change.

Meekan, Ruppert and their colleagues study coral reefs about 300 kilometers off the coast of northwest Australia, a segment of sea where Indonesian fishermen regularly target sharks, something they have done historically and continue to do today under an agreement between the Australian and Indonesian governments.

"The reefs provided us with a unique opportunity to isolate the impact of over-fishing of sharks on reef resilience, and assess that impact in the broader context of climate change pressures threatening coral reefs," said Ruppert. "Shark fishing appears to have quite dramatic effects on coral reef ecosystems.

"Given that sharks are in decline on reefs worldwide, largely due to the shark fin trade, this information may prove integral to restoration and conservation efforts."