Jonathan Ruppert, a recent University of Toronto PhD graduate, said that where shark numbers are reduced due to commercial fishing, there is also a decrease in the herbivorous fishes which play a key role in promoting reef health.
Mark Meekan, leader of the team engaged in long-term monitoring of reefs off Australia's northwest coast, said that their analysis suggested that where shark numbers are reduced, they also see a fundamental change in the structure of food chains on reefs.
"We saw increasing numbers of mid-level predators - such as snappers - and a reduction in the number of herbivores such as parrotfishes, which are very important to coral reef health because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances," Meekan said.
The reefs studied are about 300 kilometres off the coast of northwest Australia where Indonesian fishers target sharks, a practice stretching back several centuries and which continues under an Australian-Indonesian memorandum of understanding.
The researchers said that the reefs provided them with an 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.
Tracking studies show that, in many cases, individual reef sharks are closely attached to certain coral reefs. This means that even relatively small marine-protected areas could be effective in protecting the top-level predators and allowing coral reefs to more fully recover from coral bleaching or large cyclones which are increasing in frequency due to the warming of the oceans as a result of climate change.
The study will appear in journal PLOS One.
--ANI (Posted on 20-09-2013)