Mera, Hanaka, Edwards, Alasdair J., Guest, James R., Lachs, Liam, Quigley, Kate M., Willis, Bette L., and Baird, Andrew H. (2025) Patterns of coral spawning in the Palm Islands, Great Barrier Reef. Coral Reefs, 44. pp. 1789-1803.

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Abstract

Scleractinian reproductive biology has been a focus of research since the discovery of multi-species synchronous spawning in the early 1980s; however, predicting when colonies will spawn on the Great Barrier Reef remains problematic. Here, we combine over 30 years of direct coral spawning observations that include colonies from 128 species from 44 genera in 10 families with 20 years of data on the stage of gamete maturity in colonies of Acropora (hereafter, colony reproductive condition) from the Palm Island group on the Great Barrier Reef to explore patterns within and among species. We find the lunar month counted from the southern hemisphere winter solstice better predicts the first month of spawning in the Palm Islands than the Gregorian month: spawning was never observed before the 5th lunar month. Direct observations suggest that most coral spawning in the Palm Islands occurs in the 5th and 6th lunar months over a 12-day interval starting one day before the full moon, between 30 min before and 5 h after sunset. Split spawning was also a frequent occurrence in Acropora populations. Some Acropora spp. had colonies that spawned in four or five different lunar months, a pattern that might be affected by taxonomic uncertainty. The range in spawning start times was considerably greater among colonies maintained in the laboratory vs those in the field, suggesting that spawning times are affected by handling. This work highlights the importance of a systematic approach to documenting spawning times to improve our understanding of spawning synchrony and seasonality.

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