Understanding and managing species range shifts: first observed mixed-species outbreak and coral predation by crown-of-thorns starfish (Acanthaster brevispinus and A. cf. solaris) on subtropical reefs

Climate change is forcing scientists and natural resource managers to contend with species range shifts and altered species interactions. These range shifts are difficult to detect and can have unexpected consequences, especially when range expanding predators feed on resident species. On tropical western Pacific coral reefs, outbreaks of the coral-eating crown-of-thorns starfish, Acanthaster cf. solaris, cause widespread coral loss. Here we document the poleward range expansion of its close relative Acanthaster brevispinus, often a non-coral-eating species, to the subtropics of eastern Australia (30°S). In this region, corals grow directly on rocky substrate and persist in marginal conditions at their poleward range limits. We recorded the first mixed species outbreak of A. brevispinus and A. cf. solaris (91 and 39 starfish, respectively) where both species preyed on a broad diet of primarily endemic and high-latitude corals. The unusually broad diet of the two predator species compounded the detrimental effects on vulnerable high-latitude coral asemblages, which host many long-lived and slow-growing coral species that will be slow to recover (e.g., Paragoniastrea australensis, Acanthastrea echinata, Micromussa lordhowensis, Astrea curta). Both crown-of-thorns species also preyed on other cnidarian species including zoanthids and corallimorpharians. We show that collaborative efforts across marine resource managers, researchers, dive operators, and citizen scientists facilitated adaptive management that led to the swift control of the outbreak to protect vulnerable high-latitude coral assemblages. This highlights the success of cross-jurisdictional, cooperative management in adapting to the challenge of species redistribution under climate change.