Impacts of ocean warming on the settlement success and post-settlement survival of Pacific crown-of-thorns starfish ( Acanthaster cf. solaris )

Ocean warming and population irruptions of crown-of-thorns starfish (CoTS; Acanthaster cf. solaris ) are two of the greatest threats to coral reefs. As such, there is significant interest in understanding how CoTS may be directly impacted by rising ocean temperatures. Settlement of planktonic larvae and subsequent metamorphosis is purported to be a major population bottleneck in marine invertebrates, yet it is unknown how ocean warming will impact these processes in CoTS. Herein, the effect of temperature (28 °C ambient, 30 °C, 32 °C, 34 °C) on the settlement success, metamorphic success, and post-settlement survival of this corallivore was explored. While larval settlement was robust to elevated temperature, with at least 94% of larvae settling after 48 h across all temperatures, it was observed that settlement success was lower on substrate that had been pre-treated ≥ 32 °C. Metamorphic success was also significantly constrained at temperatures ≥ 32 °C. At 32 °C and 34 °C metamorphic success was 16% and 63% lower than at ambient temperature, respectively. Significant adverse effects of warming on post-settlement survival were observed at even cooler temperatures, with 10% lower survival at 30 °C compared to at ambient temperature, and at 34 °C, survival was 34% lower. Substantial reductions in metamorphic success and early post-settlement survival at elevated temperatures, as well as negative impacts of warming on the settlement substrate and its capacity to induce settlement, may present a bottleneck for recruitment in a warmer ocean.