Phase shift of larval release by pocilloporid corals in a semi-enclosed embayment with spring tide induced upwelling

The timing of reproduction could reflect local adaptations to environmental conditions so as to optimize reproductive success. We examined the annual and lunar patterns of larval release by two pocilloporid corals, Pocillopora damicornis and Seriatopora hystrix, in Nanwan Bay, southern Taiwan, a semi-enclosed embayment with spring tide induced upwelling. Corals were collected from the field and maintained in outdoor, flow-through systems to quantify the daily release of planulae. The two species showed similar reproductive pattern of tight synchronization and monthly phase shift in lunar cycle of larva release. The peak of larva release occurred around the full moon, spring tide phase in winter, shifted forward to around the first quarter moon, neap tide phase in summer, then reversely shifted backward to around the full moon, spring tide phase in winter. The peak of larvae release occurred around the first quarter moon and neap tide phase during summer might be beneficial for minimizing the negative effect of releasing larvae into unfavorable water conditions resulted from upwelling which caused suddent temperature fluctuations around the new and full moon, spring tide phase during summer. It suggests that phase shift of larval release might be an adaptive strategy. Furthermore, knowing the reproduction and settlement information available, it would be practical to obtain a large number of competent larvae, seed them on suitable substrata, and restore damaged coral populations and communities.