Effect of a fluctuating thermal regime on adult and larval reef corals

We compared responses of adults and larvae of the brooding corals Pocillopora damicornis and Seriatopora hystrix to 12-h exposures to constant temperature treatments (21 degrees C, 28 degrees C, or 30 degrees C) and a treatment in which temperature fluctuated from 28 degrees to 21 degrees C, simulating daily temperature variation generated by tidally driven upwelling in their natural habitat (Nanwan Bay, southern Taiwan). In all treatments, the maximum dark-adapted quantum yield of photosystem II (F-V/F-M) of the larvae was similar to 49% lower than that of adult corals; F-V/F-M in the larvae also differed among temperature treatments, with the highest values in the fluctuating treatment. These results show that the larvae of at least P. damicornis are more sensitive to temperature than adults, and suggest that larvae are physiologically well suited to fluctuating temperature regimes. To assess whether the timing of larval release affected their performance, larvae of P. damicornis were compared among release days within a single reproductive event. Groups of larvae released on nine consecutive days differed significantly in size, Symbiodinium content, and F-V/F-M. This demonstration of functional differences among coral larvae that are released on different dates within a single reproductive event creates the potential for advantages to accrue from the coincidence of larval phenotypes with temporally varying conditions. Adult colonies may experience selective advantages by producing broods of functionally variable larvae, in order to match extreme phenotypes to unusual environmental conditions.