Novel rubble-dwelling predators of herbivorous juvenile crown-of-thorns starfish (Acanthaster sp.)

Abstract

Crown-of-thorns starfish (CoTS) are a pervasive coral predator prone to population outbreaks that have damaged coral reefs across Australia and the wider Indo-Pacific. CoTS population control through predation has been suggested as a primary mechanism that suppresses their outbreaks. However, the nature and rates of predation on CoTS are poorly resolved, especially for early life-history stages where they are expected to be most vulnerable. Here, we provide results from the first investigation of predators of CoTS during their rubble-dwelling, herbivorous, juvenile phase. We assessed the capacity of 104 common species of the rubble cryptofauna found across Heron Reef, Great Barrier Reef, Australia, to consume early-stage juvenile CoTS (0.8–3.8 mm) using controlled feeding experiments with laboratory-raised juveniles. We identified 26 novel CoTS predators, but only 10 species that regularly consumed juvenile CoTS in their entirety. Most cases of predation resulted in severed bodies and missing arms (i.e. sublethal predation) but not total consumption. We highlight one crustacean predator, Schizophrys aspera, the red decorator crab, which consumed whole juvenile CoTS in 89% of feeding trials and in excess of 5 CoTS d−1 in natural rubble mesocosms with alternative prey. This work emphasises the importance of predators at the critical juvenile stage that may control the build-up of CoTS populations prior to being detectable as an outbreak population.