Managing cross-scale dynamics in marine conservation: Pest irruptions and lessons from culling of crown-of-thorns starfish (Acanthaster spp.)

The global degradation of natural ecosystems is leading to an increased focus on interventionist management and habitat restoration. On coral reefs, a foremost example of this trend is the extensive culling of crown-of-thorns starfish (Acanthaster spp.), which are native to coral reefs throughout the Indo-Pacific. At high densities, following population irruptions, crown-of-thorns starfish consume large areas of live coral, contributing to sustained and widespread degradation of reef environments. While population irruptions of crown-of-thorns starfish may be exacerbated by anthropogenic activities, their deleterious effects on reef systems are symptomatic of broad scale habitat degradation and loss of resilience. Extensive culling of crown-of-thorns starfish is justified as a way to offset distal drivers of coral reef degradation, but the demonstrated effectiveness of culling in small and isolated habitat patches has limited viability at the scale of entire reef systems, given the considerable effort required (upwards of 800 h.km²) and no evidence of increased efficiencies with scale. Here we draw on ideas from the management of irruptive species in other systems to develop an alternative perspective on population irruptions of Acanthaster spp., focusing on the sequential thresholds that lead to landscape-scale population irruptions. Strategic management to prevent early precursors to population irruptions may represent the most feasible approach to preventing or containing these disturbances. However, permanent or long-term solutions will require a deeper, more holistic consideration of the multitude of factors that contribute to population irruptions of crown-of-thorns starfish across a hierarchy of different scales.