Coral reefs worldwide are threatened by thermal stress caused by climate change. Especially devastating periods of coral loss frequently occur during El Niño‐Southern Oscillation (ENSO) events originating in the Eastern Tropical Pacific (ETP). El Niño‐induced thermal stress is considered the primary threat to ETP coral reefs. An increase in the frequency and intensity of ENSO events predicted in the coming decades threatens a pan‐tropical collapse of coral reefs. During the 1982–1983 El Niño, most reefs in the Galapagos Islands collapsed, and many more in the region were decimated by massive coral bleaching and mortality. However, after repeated thermal stress disturbances, such as those caused by the 1997–1998 El Niño, ETP corals reefs have demonstrated regional persistence and resiliency. Using a 44 year dataset (1970–2014) of live coral cover from the ETP, we assess whether ETP reefs exhibit the same decline as seen globally for other reefs. Also, we compare the ETP live coral cover rate of change with data from the maximum Degree Heating Weeks experienced by these reefs to assess the role of thermal stress on coral reef survival. We find that during the period 1970–2014, ETP coral cover exhibited temporary reductions following major ENSO events, but no overall decline. Further, we find that ETP reef recovery patterns allow coral to persist under these El Niño‐stressed conditions, often recovering from these events in 10–15 years. Accumulative heat stress explains 31% of the overall annual rate of change of living coral cover in the ETP. This suggests that ETP coral reefs have adapted to thermal extremes to date, and may have the ability to adapt to near‐term future climate‐change thermal anomalies. These findings for ETP reef resilience may provide general insights for the future of coral reef survival and recovery elsewhere under intensifying El Niño scenarios.

Long-distance dispersal is believed to strongly influence coral reef population dynamics across the Tropical Pacific. However, the spatial scale and strength at which populations are potentially connected by dispersal remains uncertain. To determine the patterns in connectivity between the Eastern (ETP) and Central Tropical Pacific (CTP) ecoregions, we used a biophysical model incorporating ocean currents and larval biology to quantify the seascape-wide dispersal potential among all population. We quantified the likelihood and determined the oceanographic conditions that enable the dispersal of coral larvae across the Eastern Pacific Barrier (EP-Barrier) and identified the main connectivity pathways and their conservation value for dominant reef-building corals. Overall, we found that coral assemblages within the CTP and ETP are weakly connected through dispersal. Although the EP-Barrier isolates the ETP from the CTP ecoregion, we found evidence that the EP-Barrier may be breached, in both directions, by rare dispersal events. These rare events could explain the evolutionary genetic similarity among populations of pocilloporids in the ecoregions. Moreover, the ETP may function as a stronger source rather than a destination, providing potential recruits to CTP populations. We also show evidence for a connectivity loop in the ETP, which may positively influence long-term population persistence in the region. Coral conservation and management communities should consider eight-key stepping stone ecoregions when developing strategies to preserve the long-distance connectivity potential across the ETP and CTP.

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 Niño and La Niña events and future ocean warming.

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