Abstract
Broadcast-spawning scleractinian corals annually release their gametes with high levels of synchrony, both within and among species. However, the timing of spawning can vary inter-annually. In particular, the night of spawning relative to the full moon phase can vary considerably among years at some locations. Although multiple environmental factors can affect the night of spawning, their effects have not been quantitatively assessed at the multi-regional level. In this study, we analysed environmental factors that are potentially correlated with spawning day deviation, in relation to the full moon phase, in Acropora corals inhabiting seven reefs in Australia and Japan. We accordingly found that sea surface temperature and wind speed within one to two months prior to the full moon of the spawning month were strongly correlated with spawning day deviations. In addition, solar flux had a weak effect on the night of spawning. These findings indicate that Acropora have the capacity to adjust their development and physiology in response to environmental factors for fine-tuning the timing of synchronous spawning, thereby maximizing reproductive success and post-fertilization survival.
Highlights
Inter-annual variations in environmental conditions, e.g. temperature and photoperiod, can lead to shifts in the phase and amplitude of the seasonal oscillations of biological events
The spawning day deviation varied across reefs, with the mean deviation in Otsuki being highest among all seven reefs (+7.167 DAFM) and that in Sekisei Lagoon being lowest (+0.8571)
When we assessed the difference in the Akaike information criterion (AIC) values between the selected best model and the null model (ΔAIC), the best model of time range (1) showed the highest ΔAIC value among the four time ranges
Summary
Inter-annual variations in environmental conditions, e.g. temperature and photoperiod, can lead to shifts in the phase and amplitude of the seasonal oscillations of biological events. The daily means of 10 m above surface wind speed (m s−1) and rate of precipitation (mm h−1) at a 0.25° spatial resolution were derived from the Tropical Rainfall Measuring Mission’s (TRMM) Microwave Imager (TMI) by the NASA Earth Sciences Program and were recorded using Remote Sensing Systems These daily environmental parameters were obtained for the years 2003–2014 and used in subsequent analyses (electronic supplementary material, table S3). The mean values of each variable were calculated for four different time ranges: (1) −1 to −30, (2) −31 to −60, (3) −61 to −90 and (4) −91 to −120 days after the full moon of the month of the first spawning (DAFM) for each year (see electronic supplementary material, figure S1 for details) These time ranges were selected so as to cover the late stage of gametogenesis in Acropora corals [2,14], allowing us to examine in which range the environmental factors well explained the spawning day deviation. All analyses were performed using R v. 3.5.1 [21]
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