The ecological importance of intact top-predator populations: a synthesis of 15 years of research in a seagrass ecosystem

Theworldwide decline of large-bodiedmarine taxa hasmade it difficult to draw conclusions about the relative importance of top-down control, and the mechanisms through which it might operate, in coastal marine ecosystems. Since 1997, the Shark Bay Ecosystem Research Project has used the relatively pristine seagrass community of Shark Bay, Australia, to investigate the potential for tiger sharks, the apex predator in the ecosystem, to have an impact on their largebodied prey through non-consumptive (‘risk’) effects. Here, we synthesise nearly 15 years of data to demonstrate that tiger sharks have widespread risk effects on both large-bodied herbivores and mesopredators in Shark Bay and explore the possibility that these impacts may cascade to lower trophic levels. Although much work remains to be done, our studies suggest that losses of top predators in subtropical estuaries may have greater consequences than generally appreciated and that efforts to conserve and restore their populations should be a priority. Furthermore, future management strategies and studies must explicitly consider the potential for predators to influence behaviour of even large-bodied marine taxa. Additional keywords: behaviourally mediated indirect species interactions (BMII), community dynamics, dugong, Indo-Pacific bottlenose dolphin, non-consumptive effects, risk effects, tiger shark. Received 27 January 2012, accepted 21 June 2012, published online 26 November 2012