Abstract
Split spawning in coral populations occurs when gamete maturation and mass spawning are split over two consecutive months. While split spawning has been observed at many reefs, little is known about the frequency and significance of these events. Here we show that split spawning occurred frequently and predictably over a decade at Scott Reef. Split spawning overlays the biannual spawning pattern in the region and occurs when the full moon falls in the first week of the usual spawning month, or the last week of the previous month. Additionally, in split years most species have their main spawning event after a 13-month lunar cycle, in the month following the usual spawning month. Without split spawning, spawn dates would shift by ~10 days each year to occur outside of optimal environmental windows. Our results suggest that split spawning is driven by a disconnect between lunar and seasonal cues, and is analogous with a ‘leap year’ in coral reproduction, realigning spawning dates with favourable conditions for reproduction.
Highlights
Split spawning in coral populations occurs when gamete maturation and mass spawning are split over two consecutive months
Pharoah and Willis[26] tracked long-term patterns of split spawning for the central Great Barrier Reef (GBR). They recorded split spawning when the full moon fell in the first half of the month and hypothesised that spawning was tracking lunar patterns (12 or 13 lunar months) in order to maintain reproduction within favourable conditions
In mass spawning years, spawning occurred in March and October (2008, 2009, 2011 and 2014), while in split spawning years autumn spawning was split between March and April and spring spawning was split between October and late October/November (2007, 2010 and 2015)
Summary
Split spawning in coral populations occurs when gamete maturation and mass spawning are split over two consecutive months. At some reefs, where spawning of the coral community is less synchronised, sequential spawning events of species assemblages occur over several months within a spawning season[11,14,18,19]. There does not appear to be a consistent relationship between the timing of the full moon and the occurrence of split spawning, and this relationship is probably unique to each reef It is unknown what proportions of colonies spawn in each month of a split spawning event and it is unknown how significant these events are for reef renewal. Our findings show that split spawning is occurring frequently and predictably, according to the timing of the full moon, in both spawning seasons at Scott Reef and that the main spawning event in a split year is the second month, not the ‘usual’ spawning month. Split spawning occurs after 13 lunar months instead of 12 lunar months, having the effect of realigning the spawning date within the optimal environmental window for successful fertilisation and recruitment
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