Annual variation in the timing of coral spawning in a high-latitude environment: influence of temperature

This study was conducted at a high-latitude location (32°N; Kochi, Japan), where annual seawater temperatures show large fluctuations due to the meandering of the Kuroshio Current, providing a unique opportunity to examine the influence of temperature on coral reproduction. Annual spawning of individual colonies of four reef coral species-two Acropora species (Acropora hyacinthus and A. japonica) and two faviid species (Favites pentagona and Platygyra contorta)-was monitored in situ for 4 years in 2006-2009. The spawning of the four species always occurred around the last quarter moon in the local summer, July or August, irrespective of high annual variations in seawater temperatures (from 23.7 to 29.5 °C) and weather during the spawning period. However, the exact timing of spawning during the spawning period varied among the years and was correlated with the cumulative seawater temperature during the late period of gametogenesis (0-3 months before spawning). When seawater temperatures were higher, spawning occurred in the earlier spawning month (July) and vice versa, except in A. hyacinthus, which always spawned in July. In the case of the two Acropora species, higher (lower) temperatures led to spawning earlier (later) in the lunar cycle. Seawater temperature may have an influence on gametogenesis, causing the shift in spawning timing.