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).