Plasticity in lunar timing of larval release of two brooding pocilloporid corals in an internal tide-induced upwelling reef

The environmental conditions in shallow marine environments vary on multiple temporal scales, but under the influence of climate change, these conditions are likely to change in frequency and magnitude. Phenotypic plasticity is one mechanism by which organisms can respond to this complex environmental challenge. Plasticity of reproductive timing may have beneficial value, especially for species that reproduce multiple times annually. In this study, we quantified the lunar periodicity of larval release by 2 brooding reef corals, Pocillopora damicornis and Seriatopora hystrix, in Nanwan Bay, southern Taiwan, from 2003 to 2008. Larval release was highly synchronized for both species, with lunar timing of monthly larval release varying among tidal phases, seasons and years that differed in seawater temperature. Lunar date of peak larval release for both species was related non-linearly to mean monthly seawater temperature, with release day advancing as temperature increased from winter (23 degrees C) to summer (28 degrees C). In the winter, peak release of larvae mainly occurred after the first quarter moon, with occasional larval release after the full moon, but in the summer, peak larval release occurred around the first quarter moon and neap tide. Since Nanwan Bay is strongly affected by intermittent upwelling induced by internal tides, the shift in reproductive timing may allow larvae released in the summer to avoid the negative thermal effects of upwelling and may also favor local retention.