Feeding preferences and growth in herbivorous juvenile crown-of-thorns sea stars (Acanthaster cf. solaris)

Abstract Crown-of-thorns sea stars (CoTS; Acanthaster spp.) are among the most prominent corallivorous invertebrates, contributing greatly to the plight of tropical coral reefs in the Anthropocene. Much of the success of CoTS, and their propensity to undergo major population irruptions, are likely tied to inherent biological traits. Juvenile CoTS feed on coralline algae prior to their ontogenetic switch to corallivory, but their feeding preferences for specific algae and the implications thereof remain unresolved. Here, we conducted 48-hour multiple-choice and 28-day no-choice experiments to compare the selection and consumption of different crustose coralline algae (CCA) diets by juvenile western Pacific CoTS ( Acanthaster cf. solaris ), and test for concomitant differences in growth rates. In the multiple-choice experiment, juvenile CoTS preferentially consumed the alga Melyvonnea cf. madagascariensis , whilst avoiding Sporolithon sp., Lithophyllum cf. kotschyanum , and Adeylithon cf. bosencei . Daily consumption rates during the no-choice experiment varied substantially among CCA species, ranging from 15.31 mm 2 ind −1 d −1 (± 2.68) (mean ± SE) for M . cf. madagascariensis to 1.38 mm 2 ind −1 d −1 (± 0.24) for Sporolithon sp. This preferential consumption of different CCA corresponded well with large differences observed in the surface area growth rate of CoTS, ranging from 3.01% d −1 (± 0.30) to 0.08% d −1 (± 0.33) for juveniles feeding on M . cf. madagascariensis and Sporolithon sp., respectively. Organic carbon and nitrogen content of different CCA species did not influence CCA consumption rates or CoTS growth rates. However, CoTS growth rates were positively correlated with daily consumption rates of both organic carbon and nitrogen due to preferential feeding. Our results suggest that the prevalence and consumption of some CCA species, particularly M . cf. madagascariensis , a species that is common on mid-shelf reefs of the Great Barrier Reef, may boost early post-settlement growth and survival of herbivorous juveniles, and thereby contribute to the population build-up of CoTS.