Bet- hedging reproduction strategies in the massive Caribbean coral Favia fragum

Bet- hedging has long been recognised as an adaptive mechanism in unpredictable environments, yet is often overlooked as an evolutionary strategy in corals to adapt to environmental conditions associated with climate change. Most environments vary spatially and temporally over the lifespan of corals, and corals use cues from their natal environments as “predictors” of the environment they will release their offspring into and may optimise phenotypes to maximise fitness to changes in the maternal environment. However, when conditions fluctuate in unpredictably or environmental cues are otherwise lost, producing a single phenotype could cause population bottlenecks. Prolonged summer periods of high sea surface temperatures combined with anthropogenic impacts are inhibiting environmental cues that have previously secured reproductive success in tropical scleractinian corals and enabled them to fine-tune their reproductive patterns to time periods that optimize external fertilization success, appropriate larval dispersal and efficient coral recruitment. This study tested the ability of the brooding species Favia fragum to “hedge their bets” on reproductive strategies in the presence/ absence of lunar cues, a cue known to play an important role in synchronizing reproductive output. Results illustrated F. fragum exhibited dynamic bet-hedging, tailoring larval output and producing a range of larval phenotypes and thus exhibiting plasticity dependent on their environment. In the absence of lunar cues, corals varied the timing of planulae release as well as within-clutch size variation promoting dispersal and retention to their natal environment. Lunar stimulated corals concentrated release to 3-6 days, typically produced a single phenotype aiding retention and re-seeding local reef populations. Reproductive flexibility will enable coral to strategize larval/ gamete release that optimise recruitment success within unstable environmental conditions. The use of such strategies in other brooding species and broadcast spawners should be a focus of further investigation to evaluate the potential for corals to populate environments beyond the familiar and persist future unpredictability