Changes in quantum efficiency of Photosystem II of symbiotic dinoflagellates of corals after heat stress, and of bleached corals sampled after the 1998 Great Barrier Reef mass bleaching event
Rj. Jones et al., Changes in quantum efficiency of Photosystem II of symbiotic dinoflagellates of corals after heat stress, and of bleached corals sampled after the 1998 Great Barrier Reef mass bleaching event, MAR FRESH R, 51(1), 2000, pp. 63-71
Pulse-amplitude-modulation chlorophyll fluorometry was used to examine chan
ges in dark-adapted F-v/F-m of endosymbiotic dinoflagellate microalgae with
in the tissues of the temperate coral Plesiastrea versipora exposed to elev
ated seawater temperature. The F-v/F-m was markedly reduced following expos
ure of corals to 28 degrees C for 48 h. When corals were returned to ambien
t (24 degrees C) conditions, F-v/F-m increased in an initial rapid and then
secondary slower phase. Tissue discolouration (coral bleaching), caused by
a significant decrease in the density of algae, was observed during the fi
rst 2-3 days of the recovery period. After 14 days, F-v/F-m was still signi
ficantly lower than in control corals. The recovery of F-v/F-m is discussed
in terms of repair processes within the symbiotic algae, division of healt
hy algae and also the selective removal of photo-damaged dinoflagellates. U
nder field conditions, bleached corals sampled at Heron Island Reef during
a bleaching event had significantly lower F-v/F-m than non-bleached colonie
s; four months after the bleaching event, there were no differences in F-v/
F-m or algal density in corals marked as having bleached or having shown no
signs of colour loss. The results of this laboratory and field study are c
onsistent with the hypothesis that an impairment of photosynthesis occurs d
uring heat-stress, and is the underlying cause of coral bleaching.