33
1994
2100
Supersaturation
Undersaturation
Aragonite saturation
Sources: Donner, S.D.,
et al.,
2005; Orr, J.C., 2005.
Map by Hugo Alhenius.
Coral bleaching is a phenomenon caused primarily by above-average water temperatures and high radiation
from the sun, that stress the micro-algae (“zooxanthellae”) living symbiotically in corals and giving them
their spectacular colours. When these micro-algae become stressed, the coral expels them, so that the coral’s
white calcareous skeleton is visible through the transparent tissue – hence the term ‘bleaching’. Bleached
corals are very weak and prone to disease, algal overgrowth and mortality if the stress is high or continues
over longer time periods. In 1998, a mass global bleaching event caused the mortality of an estimated 16%
of the world’s coral reefs, and unfortunately because of rising sea temperatures mass bleaching events are
predicted to increase in frequency and intensity. Loss of coral reefs also means loss of revenue and food for
coastal communities who depend on them.
LOSS OF CORAL REEFS AND
ASSOCIATED MARINE BIODIVERSITY
7
1994
2100
Supersaturation
Undersaturation
Aragonite saturation
Sources: Donner, S.D.,
et al.,
2005; Orr, J.C., 2005.
Map by Hugo Alhenius.
Figure 15. Ocean
acidification
– as
carbon concentra-
tions increase in
the atmosphere, so
do concentrations
in the oceans, with
resultant acidifica-
tion.
Source: Donner, S.D., et al., 2005; Orr, J.C., 2005.
