Predator morphology dictates allometric scaling of predation risk for a keystone marine invertebrate

Predation is a significant source of mortality for many prey taxa, but predation strength may be determined by predator-prey body size, functional morphology or their combination. Here, we explore the relative contribution of predator-prey sizes and morphology in determining predation risk and density-dependent consumption rates for 5 decapod predators of juvenile crown-of-thorns starfish (CoTS; Acanthaster sp.), a corallivorous pest species common across the Indo-Pacific. We found generalisable patterns in the allometric scaling of predation risk among predator species, with declining consumption probability as juvenile CoTS size increased and predator size decreased. However, distinct predator claw characteristics explained 2 contrasting foraging styles that modified allometric predation windows and constrained attack rate and handling time estimates. Frequent CoTS injury and relatively low consumption rates (1.4-3.6 CoTS d -1 ) typified interactions with Portunidae species, whose sharp, weak claws are largely ineffective for consuming benthic prey. By contrast, the red decorator crab Schizophrys aspera (Majidae) consumed larger quantities of CoTS (16.8-22.1 CoTS d -1 ) across a broader range of prey sizes (1-14 mm), at least in part due to specialised spatulate claws that appear well-suited for handling benthic prey. Our results suggest that predator-induced CoTS mortality is strongest for juveniles < 5 mm when multiple predators are capable of total consumption, but CoTS vulnerability may be prolonged in the presence of S. aspera . Variation in the abundance of these 2 predator types may impact overall juvenile cohort success and the time to reach size refuges, with consequences for CoTS outbreaks.