Impact of climate change on the potential for localized recruitment in reef corals

Background/Question/Methods

The recovery of coral populations following disturbance depends largely on larval recruitment success. Populations on sink reefs or on reefs with higher levels of larval retention should recover faster. Global warming is likely to have impacts on the levels of larval retention as higher temperatures are known to accelerate the metabolism and development of several marine invertebrates. We tested the effect of temperature on the larval settlement competence dynamics of Acropora tenuis, and estimated its impacts on potential for localized recruitment. Specifically, we collected gametes of six coral colonies of A. tenuis in Sesoko Island, Okinawa (Japan), allow them to fertilize, and cultured the larvae under four treatment regimes: 25, 27, 29 and 31°C. Each day, the proportion of competent larvae was quantified by exposing four replicate of 20 larvae (that had not been previously exposed to settlement cues) to a pre-conditioned settlement tile. After 24h, the number of larvae that had settled and metamorphosed to polyp was counted. The competence dynamics model produced was used to estimate potential for localized recruitment in reefs with a range of retention times.

Results/Conclusions

We found that temperature accelerates the acquisition of competence. Larvae reared at 31C were able to settle in 42h, while the ones reared at 25-27C took the double of the time to acquire settlement competence (81-82h). This significant difference was translated in to an increased proportion of larvae retained in the natal reef and thus an increased potential for localized recruitment and reduced dispersal and connectivity. This is more evident in reefs with short-mid retention times, i.e., retention times close to the species minimum time to acquire competence (<3.5 days). Our study suggest that as sea surface temperature increases, the recovery from regional-scale disturbances will hasten because localized recruitment will be higher and the loss to mortality of predation will decline. However, if disturbances are highly localized, the reduced connectivity (decline on recruits from undisturbed reefs) could offset the increase in localized recruitment and therefore lower recovery rates.