Temperature
Minimum temperatures at two of the study sites ranged from 13.9oC at Guy Fawkes (at 15 m) to 16.3oC (at 6 m) depth at Baltra, and were similarly low (14oC) at the Cuatro Hermanos reference site (Table 1A). Temperatures were at or below the threshold of 18oC for Pocillopora bleaching for 6.3 to 34.3 days at Baltra (6 m) and Guy Fawkes (15 m) respectively (Table 1B). At Guy Fawkes, the subtidal environments experienced the colder bleaching threshold of 16oC or lower for less than 1 hour at 6 m, but this time period increased to 54.6 hours at 15 m depth. Temperatures were colder at the Cuatro Hermanos reference site, where they were 18oC or lower for 59.5 days and 16oC or lower for 5.3 days (Table 1B).
Satellite images of minimum sea surface temperatures (SST) confirmed our temperature logger data and depicted a cold-water plume moving northwest along the South American Coast and deflecting offshore to reach our study area in the central Galápagos. During August-October 2007 the minimum SST of 15-20oC occurred (Figure S2). This was likely the origin of the cold water that led to coral bleaching, given that we recorded substantial temperature declines at 6 and 15 m depth during this same time period (Figure 1). By January 2008, the minimum SST had increased to 20-25oC (Figure S2).