Assigning causality to events in the Holocene record of coral reefs

The uncemented reef-frameworks of Pacific Panamá, which have been dominated throughout the Holocene by branching corals of the genus Pocillopora, experienced a hiatus in vertical accretion lasting c. 2300 years, beginning c. 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 c. 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 the hiatus was not solely an artefact of bioerosion; rather, a long-term increase in ENSO variability suppressed coral growth and vertical reef accretion.