Artificial bleaching was induced by maintaining the
corals under water and exposing a small (1.0 cm2
)
smooth surface of each sample to 1500 µmol photons
m–2 s–1 of light while covering the rest of the coral surface
with aluminum foil for 6 h (method adapted from
that of Yamasaki et al. [1995] for tropical higher
plants). Partial colony bleaching, similar that induced
by this experimental procedure, is common during
sublethal thermal stress events, as evidenced on the
Great Barrier Reef (Heron Island) in February 2002
(van Woesik pers. obs.). To generate this high light
level, we used cold-lighting fiber-optic tubes equipped
with a UV filter (NPI, Picl-nex; Phillips, projection lamp
150 W) placed 3 cm above the surface of the water.
Samples were immersed and held close (1 cm) to the
surface of a 5 l water bath (TAITEC, SM-05R) supplied
with filtered seawater; temperature was maintained at
27°C by a thermostat and homogenizing propeller.
After artificial bleaching, 3 samples (n = 1 for each
colony) were frozen and subsequently analyzed for
chlorophyll a and c2 concentrations, and zooxanthellae
numbers were counted and recorded as Week 0