Maximising the benefits of local management for coral reefs amidst near-term environmental change

Abstract

Pest species cause significant ecological and economic damage globally. The Crown-of-Thorns starfish (CoTS; Acanthaster spp) drives coral mortality across the Indo-Pacific, including on the Great Barrier Reef (GBR), where cyclones and bleaching also threaten coral. Manual CoTS control mitigates coral loss, but the factors driving control efficacy amidst environmental change remain uncertain. Using a spatially explicit ecosystem model of the GBR to simulate past, current, and future CoTS outbreaks (2008-2040), we compared coral cover between "CoTS control" and "no control" scenarios, and explored how control, disturbances, and ecological variables influenced outcomes. CoTS control generated cover benefits in 84.5 % of predictions, with a third of controlled reefs achieving >10 % cover gains. Benefits also increased over time. Cover deficits (15.5 %) were rare relative to benefits and generally small (<10 %). Reefs were more likely to experience benefits with increasing proportions of CoTS-preferred coral prey, frequency of control, and period between disturbances. High CoTS densities and larval supply and frequent disturbances reduced cover benefits, while rubble, coral larval supply, and control recency had limited effects. There were differences between reefs based on their geographic region, and whether they were targeted for control, with more pronounced benefits on reefs targeted for control and reefs in the north. Our results clearly demonstrate that CoTS control can generate substantial, and increasing, coral cover benefits at many reefs across the GBR to 2040, even under future climate change trajectories and, for the first time, identifies which factors contribute to the greatest cover benefits from control.

Keywords: Acanthaster spp; Adaptive management; Culling; Ecosystem model; Integrated pest management; Simulations.