The regional structure of spawning phenology and the potential consequences for connectivity of coral assemblages across the Eastern Tropical Pacific

The coral reefs of the Eastern Tropical Pacific (ETP) are some of the most geographically isolated of the world. A key to understanding their long-Term persistence and population recovery via dispersal (i.e. population connectivity), is knowing when the corals spawn in the region. To this end, we reviewed and synthesized the literature on the reproductive phenology of corals (month of spawning) and their dispersal-related characteristics to infer the potential impact on the region's functional connectivity. We classified the region into four thermal regimes based on long-Term mean sea surface temperature (SST) data: Tropical Upwelling, Thermally Stable, Equatorial Upwelling, and Seasonal. Each regime's unique spawning seasonality was then explored by quantifying the linear dependence between the number of observed spawning events and SST. Finally, the potential impact of this unique regional mismatch in spawning was illustrated using a biophysical larval dispersal model. We found spawning occurs throughout the year in the Upwelling and Thermally Stable regimes (showing low or no linear dependence with SST); whereas spawning had a strong seasonal signal in the Equatorial Upwelling and Seasonal regimes, occurring primarily in the warm months. Considering the region's mismatch in spawning phenologies, and unique dispersal traits, the simulations of coral larval dispersal across the ETP result in infrequently realized connectivity between ecoregions, low local retention and high self-recruitment, that combined with low recruitment densities in the field indicates more vulnerable populations to disturbance than previously appreciated. The strong relationship between spawning phenology and SST in some regimes suggests a greater susceptibility of these coral assemblages to extreme El Nino and La Nina events and future ocean warming.