Occasional loss of fecundity in peripheral coral populations

Reproductive ecology of scleractinian corals remains poorly known, particularly at the periphery of their distribution in temperate regions. However, understanding the reproductive mechanisms of these peripheral populations is important for assessing distributional changes such as poleward expansion in corals. Here, the reproductive status of two dominant Acropora coral species (Acropora cf. glauca and A. solitaryensis) was recorded over 8 years (2012–2019) to clarify annual changes in the fecundity of colonies and the timing of maturation at the periphery of their distribution. In addition, the hypothesis that the subsurface seawater temperature (S³T) affects the fecundity of Acropora corals was tested by examining the changes in ambient S³T and its effect on fecundity. As a result, the significant positive correlation between the average winter S³T (December–March) and fecundity was identified using a generalized linear model. The findings showed that temperate Acropora corals refrained from gametogenesis in the summer if average S³T during the previous winter was approximately 1°C lower than the long-term average during 2006–2019 (i.e., <15°C), potentially limiting the distribution of coral populations.