Spawning window and fecundity in three Acroporid corals from the environmentally variable semi-enclosed lagoon of Bouraké

The gametogenic cycle in broadcast spawning corals takes several months, with oogenesis culminating in synchronized maturation when seawater temperatures rise. Temperature is known for governing reproductive seasonality, yet little is known about how multiple stressors may affect spawning timing. The semi-enclosed lagoon of Bouraké in New Caledonia is subjected to high fluctuations in seawater temperature, pH, salinity, and oxygen, representing an ideal playground to explore possible effects of extreme environmental variability on coral gametogenesis. Here, the spawning window and fecundity metrics (i.e., colony- and polyp-level fecundity, and egg size) of Acropora tenuis, Montipora digitata, and M. stellata from Bouraké were compared with four reference sites located at variable distances from Bouraké. Results suggest that Bouraké and its nearby control site largely spawned synchronously, but there was a spawning asynchrony between Bouraké and the sites further south, in all three species. Interestingly, no reduction in the number of eggs per fecund polyp or number of fecund polyps was observed in Bouraké compared with the reference sites, in any species. However, A. tenuis and M. digitata had smaller eggs in Bouraké compared to reference sites, with possible repercussions for coral fitness. In conclusion, some reproductive traits are maintained in coral species inhabiting a highly variable environment, but smaller gametes may alter population recovery processes. Furthermore, since our data are limited to 2 yrs of observations, spawning synchronization between Bouraké and its surroundings warrant continued investigation to determine whether coral colonies from this area harbor traits that increase fitness under future climate scenarios.