The eastern tropical Pacific is oceanographically unfavorable for coral-reef development. Nevertheless, reefs have persisted there for the last 7000 years. Rates of vertical accretion during the Holocene have been similar in the strong-upwelling Gulf of Panamá (GoP) and the adjacent, weak-upwelling Gulf of Chiriquí (GoC); however, seasonal upwelling in the GoP exacerbated a climate-driven hiatus in reef development in the late Holocene. The situation is now reversed and seasonal upwelling in the GoP currently buffers thermal stress, creating a refuge for coral growth. We developed carbonate budget models to project the capacity of reefs in both gulfs to keep up with future sea-level rise. On average, the GoP had significantly higher net carbonate production rates than the GoC. With an estimated contemporary reef-accretion potential (RAP) of 5.5 mm year−1, reefs in the GoP are projected to be able to keep up with sea-level rise if CO2 emissions are reduced, but not under current emissions trajectories. With an estimated RAP of just 0.3 mm year−1, reefs in the GoC are likely already unable to keep up with contemporary sea-level rise in Panamá (1.4 mm year−1). Whereas the GoP has the potential to support functional reefs in the near-term, our study indicates that their long-term persistence will depend on reduction of greenhouse gases.

The uncemented reef-frameworks of Pacific Panamá, which have been dominated through the Holocene by branching corals of the genus Pocillopora , experienced a hiatus in vertical accretion lasting ∼2300 years, beginning ∼4100 years ago. The hiatus has been attributed to an increase in variability of the El Niño-Southern Oscillation (ENSO). We tested the alternative hypothesis that the hiatus was solely the result of bioerosion, assuming an acute disturbance halted coral growth 1800 years ago (the time at which reef accretion resumed after the hiatus) and that the entire framework remained in the taphonomically active zone at that time. We calculate that it would have taken 167-511 years for bioerosion to fully remove 2300 years-worth of framework growth under those circumstances. In fact, most of the reef-framework in Panamá is stabilized in sediment that prevents the activity of bioeroders; only the upper ∼1 m of open framework-several decades-worth of growth at most-would have been vulnerable to erosion, greatly increasing the time required to bioerode 2300 years of accumulation. We conclude that that the hiatus was not solely an artifact of bioerosion; rather, a long-term increase in ENSO variability suppressed coral growth and vertical reef accretion.

Upwelling exerts a major control on coral-reef development in the eastern tropical Pacific (ETP). Upwelling zones exhibit conditions that are detrimental to coral growth, such as low sea-surface temperatures and high levels of turbidity. During the late Holocene, the reefs in the strongly upwelling Gulf of Panamá (GoP) and the weakly upwelling Gulf of Chiriquí (GoC) experienced a climate-driven hiatus in coral growth and reef development, and strong upwelling exacerbated this hiatus in the GoP. Strong upwelling in the GoP is now acting as a buffer against thermal stress, providing a refuge from climatic warming, whereas corals in the GoC are highly vulnerable to increased thermal stress. Using ecological surveys and paleoecological data, we quantified calcification and bioerosion processes for the reefs in these two gulfs to develop carbonate-budget models. We determined the reef-accretion potential (RAP) for reefs in each gulf to project their capacity to keep pace with current and predicted future rates of sea-level rise. On average, reefs in the GoP exhibited an average RAP of 5.5 mm yr-1, which would be enough to keep pace with future rates of sea-level rise if CO2 emissions were reduced under representative concentration pathways (RCPs) 2.6 and 4.5. In contrast, reefs in the GoC exhibited an average RAP of only 0.3 mm yr-1, which is not even enough to keep pace with contemporary rates of sea-level rise in Panamá (1.4 mm yr-1). Furthermore, even if the reefs in either gulf could achieve 100% coral cover, none of them has the capacity to keep pace with RCP 8.5. Although the GoP should support reef development in the near future, reducing greenhouse-gas emissions will be essential to ensure the persistence of accreting reefs and promote the recovery of those vulnerable to net erosion.