The impacts of light and location on reproductive timing in the Orbicella species complex

Coral spawning events rely on tight synchronicity of gamete release to increase fertilization success by increasing gamete density in the water. Differences in spawning time can cause temporal reproductive isolation and minimize hybridization with closely related coral species. Sexual reproductive success is important as it generates the genetic diversity necessary for corals to survive large scale environmental stressors such as heat waves and bleaching events. The coordination of coral spawning events within a population maintains species boundaries and increases ecosystem-wide genetic diversity. Here we generate a database of spawning events in conjunction with depth and geographic location of the three species in the Orbicella species complex to assess variability in reproductive timing. The dataset, gathered from published papers, restoration practitioners, scientist throughout the Caribbean, contains almost three decades of data and includes 265 reproductive events. Our findings indicate that some aspects of each spawning season (month and day after the full moon) are influenced by latitude whereas others, such as spawning time in relation to local sunset, may exhibit variation based on geographic location. Combined, our results suggest that the reproductive timeframe of Orbicella spp. is triggered by factors associated with latitudinal gradients, such as the amount of energy from the sun, but the specific time of gamete release may be connected to other environmental factors that occur at a local scale or vary year-to-year.