Sharks increase reef resilience

Healthy shark populations may aid the recovery of threatened coral reefs across the globe, according to a new study by the Australian Institute of Marine Science (AIMS).

The link has been found by long-term monitoring of reefs off Australia’s north-west 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. Dr Mark Meekan, Principal Researcher at AIMS and co-author of the publication Caught in the Middle: Combined Impacts of Shark Removal and Coral Loss on the Fish Communities of Coral Reefs that recently appeared in the scientific journal Plos One, says the result might seem strange at first glance.

“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 snapper, and a reduction in the numbers of herbivores such as parrotfish. Parrotfish are very important because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances,” Meekan said.

AIMS says 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, such as over-fishing, and from climate change.

“Tracking studies show that in many cases individual reef sharks are closely attached to certain coral reefs, so even relatively small marine protected areas could be an effective way to protect the top-level predators, which may ultimately mean that coral reefs are better able to recover from coral bleaching or large cyclones,” said Meekan, concluding: “This makes the declines that are occurring in reef sharks due to overfishing throughout the world of great concern, because our study shows that a healthy reef means healthy populations of sharks.”

A link to the paper can be found on the Plos One website: plosone.org.
Image: Peter Verhoog, Dutch Shark Society, supplied by AIMS.

AIMS study indicates sharks increase reef resilience

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