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NEWS
Sharks increase reef resilience
Sharks mean more parrotfish, less algae and healthier coral reef regrowthResearchers at the Australian Institute of Marine Science (AIMS) who conducted monitoring surveys at Scott Reef in WA have concluded that healthy shark populations may aid the recovery of threatened coral reefs.
The link has been found by long-term monitoring of reefs off Australia's northwest coast and showed that where shark numbers were lower due to fishing, herbivores – important fishes in promoting reef health – were also significantly lower in number.
"At first glance the result might seem strange", says Dr Mark Meekan, Principal Researcher at AIMS and co-author of the publication that now appears in the scientific journal, PLOS ONE.
"However, our analysis suggests that where shark numbers are reduced we see a fundamental change in the structure of food chains on reefs. We see increasing numbers of mid-level predators – such as snappers – and a reduction in the numbers of herbivores, such as parrotfishes.
"The parrotfishes are very important because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances," he adds.
The study comes at an opportune time in the life of coral reefs, which are facing a number of pressures both from direct human-activity and climate change.
Dr Jonathan Ruppert, of the University of Toronto, explains that the reefs studied about 300 kilometres off the coast of northwest Australia are impacted by Indonesian fishers who primarily target sharks, a practice stretching back several centuries, under an Australian-Indonesian memorandum of understanding today.
"On reefs where sharks are fished we found much lower numbers of herbivorous or algae eating-fishes, providing evidence that over-fishing sharks can have detrimental knock-on effects at least for some species further down the food chain," Dr Meekan said.
"Our study shows that a healthy reef means healthy populations of sharks," Meekan concludes.
Title of paper: Caught in the middle: combined impacts of shark removal and coral loss on the fish communities of coral reefs.
Authors: Jonathan Ruppert, Michael Travers, Luke Smith, Marie-Josée Fortin and Mark Meekan.
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