Coral reef recovery in the Galápagos Islands: the northernmost islands (Darwin and Wenman)

The remote northernmost Galapagos Islands, Darwin and Wenman, exhibited well-developed coral communities in 1975, which were severely degraded during the 1982–1983 El Nino warming event. Mapping of the coral reef at Darwin, herein Wellington Reef, shows it presently to be the largest known structural reef in the Galapagos. It consists of numerous 1- to 3-m-high Porites framework towers or stacks and overlies a carbonate (coral/calcareous sediments) basement. Pre-disturbance Wellington Reef was constructed chiefly by Porites lobata and Pocillopora elegans, and Wenman coral cover was dominated by Pavona clavus and Porites lobata. Subsequent surveys in 2012 have demonstrated robust recovery in spite of ENSO thermal shock events, involving both high and low stressful temperatures that have caused tissue bleaching and mortality. No losses of coral species have been observed. Radiocarbon dating of 1- to 3-m-high poritid framework stacks, from their peaks to bases, revealed modern ages of up to 690 yr. Incremental stack growth rates ranged from 0.15–0.39 to 1.04–2.40 cm yr−1. The former are equivalent to framework accretion rates of 1.5–3.9 m Kyr−1, the latter to coral skeletal growth rates of 1.0–2.4 cm yr−1. Coral recovery in the central and southern Galapagos has been nonexistent to low compared with the northern islands, due chiefly to much higher population densities and destructive grazing pressure of the echinoid Eucidaris galapagensis. Thus, coral reef resistance to ENSO perturbations and recovery potential in the Galapagos are influenced by echinoid bioerosion that varies significantly among islands.