El Niño, echinoid bioerosion and recovery potential of an isolated Galápagos coral reef: a modeling perspective

Abstract

Wellington Reef is the northern-most and largest known coral reef in the Galapagos Islands. This study explores the recovery potential of the Wellington Reef when subjected to predicted future El Nino Southern Oscillation warming events that may cause varying degrees of coral mortality followed by sea urchin bioerosion. We developed a stochastic model that employs empirical data from the Wellington Reef and nearby sites. The model estimates CaCO3 bioerosion of individual coral colonies by the sea urchin Eucidaris galapagensis, which recently caused coral reef collapse in the central and southern Galapagos Islands. Numerous projections of the CaCO3 production potential of Wellington Reef 50 years into the future were generated using a simulation model by subjecting the Wellington Reef to El Nino Southern Oscillation warming events and a range of urchin density levels, resulting in varying degrees of coral mortality and subsequent bioerosion by E. galapagensis. Moderate increases in sea urchin abundance above current low levels were found to significantly increase the likelihood of Wellington Reef collapse. The large differences in the recovery of the Galapagos coral reefs across a small latitudinal scale where differences in local echinoid abundances exist make this study of the recovery potential of the Wellington Reef important in understanding the contrast between a resilient reef and ones that are susceptible to collapse. This study suggests a delicate tipping point for triggering an echinoderm-elevated bioerosive phase that results in the degradation of a healthy reef ecosystem.