Effect of sublethal predation on reproductive output of the crown-of-thorns starfish Acanthaster sp., with an overview of arm damage

Abstract

The extreme reproductive potential of the crown-of-thorns starfish (CoTS) Acanthaster sp. is a key trait used to explain their population outbreaks. Despite their highly defended morphology, sublethal predation is prevalent, as documented here for 2 outbreak populations in the Great Barrier Reef: Davies Reef and Lynch's Reef (arm damage 73.0 and 58.3%, respectively). It is not known how this trauma affects reproductive potential as a quantitative change in gonad production. We investigated the variability in gonad weight in the arms of uninjured CoTS. For CoTS with injured arms, we assessed the impact of arm injury and regeneration on gonad development at the level of the whole individual and among arms. The gonad index (GI) was lower in CoTS with 3 or more injured arms on Davies Reef, but not Lynch's Reef. At the level of individual arms, arm damage (25-100% of individual arm lost at Davies Reef and 10-100% at Lynch's Reef) resulted in a lower gonad weight compared to intact arms. Arms regenerating following total arm loss had a lower gonad weight than intact arms, even for arms that were 50-74% (Davies Reef) and 75-99% regenerated (Lynch's Reef). For uninjured CoTS, we show strong support for GI estimates based on extrapolation from one arm, and that inclusion of more than 4 arms resulted in marginal reduction in error. It is clear that sublethal injury can have a significant effect on gonad production in CoTS, with implications for population control given the reproductive potential of this species.