Cold water effects on corals
Our observations suggest that an ENSO-related cold-water anomaly led to
bleaching and death of finger corals. The bleaching period coincided
with the arrival of a plume of cold water (15-20oC
minimum SST) flowing up the west coast of South America, arriving in the
central Galápagos during October 2007. During this time period, corals
were exposed to temperatures at or below published cold water thresholds
for coral bleaching, including 18oC for up to 34 days
and 16oC or less for 2.3 days at Guy Fawkes (15 m
depth). Temperatures at Baltra (15 m) were at or below the
18oC threshold for 18.8 days. As expected,
temperatures decreased with depth from 6 to 15 m. Longer periods of
unusually cold water occurred at the reference site Cuatro Hermanos
(where corals are rare) likely related to the presence of stronger
upwelling currents relative to those at Guy Fawkes or Rocas Beagle
(Witman et al. 2010).
In general, cold-water coral bleaching has received less attention than
warm water bleaching, although it can cause extensive coral mortality.
For example, (González-Espinosa & Donner 2020) documented cold-water
coral bleaching at 14 sites in the Eastern Tropical Pacific alone from
1998 -2017. One of these events was reported from the northern islands
of Darwin and Wolf in the Galápagos where bleaching of three coral
species (Porites lobata, Pocillopora spp. and Pavona
clavus ) occurred in 2007 when SST were 16oC (Glynn
2009, Glynn et al. 2017), which was likely caused by the same La Niña
event reported in this study. Given that climate models predict that the
frequency of extreme La Niña events and associated cold-water anomalies
will increase with climate warming (Cai et al. 2015), our study suggests
that more attention should be paid to the consequences of coral
bleaching caused by low temperatures.