Published online by Cambridge University Press: 21 July 2017
Coral reefs have experienced a profound shift in community structure in recent decades, a pattern that contrasts with the apparent constancy of Caribbean reef zonation over the past 2 million years. The abrupt decline in branching Acropora palmata and massive frame-builders like Montastrea annularis in the Caribbean is troubling, and similar patterns have been reported from virtually every ocean. As we ponder the future of coral reefs, we must be mindful that our best monitoring records span perhaps half a century – and those are exceedingly rare. “Pristine” reefs may not have existed since Columbus sailed for the new world, and anthropogenic impacts probably extend even farther back in time.
Despite the vagaries of evolutionary change, taphonomy and time averaging, the geologic record still represents a unique source of important information about the processes that have controlled community structure and reef building in the absence of human influences. The creation of rigid and elevated structures requires calcification rates that are capable of filling the accommodation space created by rising sea level. This has been complicated over the past three to four decades as accelerated sea-level rise has been joined by a suite of stresses that probably slow accretion. Explaining the recent reef decline and posing realistic models of future change will require an understanding of carbonate cycling in the past, the processes that have been involved and a quantitative assessment of how anthropogenic stresses are affecting both.
At the least a look back in time may help to constrain the thresholds at which change might be expected to occur in the future. At best, the context gained from examining the “recent” geological past may provide insights into which possible solutions are most consistent with observed patterns at larger spatial and temporal scales.