Control efforts of crown-of-thorns starfish outbreaks to limit future coral decline across the Great Barrier Reef

Crown-of-thorns starfish (CoTS) naturally occur on coral reefs throughout the Indo-Pacific region. On Australia's Great Barrier Reef (GBR), outbreaks of CoTS populations are responsible for ecologically significant losses of corals, and while they have been documented for decades, they now undermine coral recovery from multiple stressors, especially anthropogenic warming. Culling interventions are currently the best approach to control CoTS outbreaks on the GBR, but assessing control effectiveness under multiple stressors is complicated. Using an ensemble of two reef community models simulating the temporal and spatial dynamics of CoTS and corals under future climate scenarios, we evaluate the present-day and future effectiveness of the current implementation of the GBR CoTS Control Program. Specifically, we determine the culling effort needed (i.e., number of vessels) to achieve the maximum ecological benefits as predicted by the models under possible warming futures. Benefits were measured by comparing projections of coral cover and CoTS densities under scenarios of increasing control effort and baseline scenarios where no control was simulated. Projections of present-day control efforts (five vessels) show that the number of individual reefs subject to CoTS outbreaks is reduced by 50%-65% annually, yielding a benefit of 5%-7% of healthy GBR coral area per decade, equivalent to gaining 104-150 km(2) of live corals by 2035. A threefold increase in current control efforts is sufficient to reach more than 80% of the maximum coral benefits predicted by each model, but the future amount of effort required to control CoTS effectively depends on the intensity of warming and the early detection of CoTS outbreaks. While culling CoTS across the entire GBR is unfeasible, we provide a framework for maximizing ecosystem-wide benefits of CoTS control and guide management decisions on the required culling effort needed to reduce CoTS outbreaks to levels that may ensure coral persistence in the face of future climate change impacts.