Environmental cues in coral reproduction: photoperiod and seawater temperature influence oocyte development in <i>Acropora tenuis</i>

In subtropical regions, a full gametogenesis cycle in corals takes 11-12 months to complete. Thus, the different stages of the gametogenesis process occur under differing light and seawater temperature conditions over the course of 1 year. Here, we show how photoperiod length and seawater temperature influence coral gametogenesis in the scleractinian coral Acropora tenuis using molecular and histological analyses. Changing the number of daylight hours showed that a longer photoperiod (14L : 10D) significantly upregulated the germ-cell genes Piwi. For seawater temperature, the effect was dependent on the stage of maturation; low seawater temperatures (21°C) were necessary for vitellogenesis in immature (non-vitellogenic) coral nubbins, and warming seawater temperatures (25-29°C) accelerated oocyte maturation in vitellogenic corals. These findings show that longer photoperiods in summer enhance germ-cell activity, low seawater temperature during winter is essential for initiating yolk formation, and warmer temperatures during early summer trigger oocyte maturation in A. tenuis. Therefore, our findings indicate that photoperiod and seawater temperature play important roles in regulating gametogenesis in A. tenuis.