CLIMATE CHANGE AND OCEAN ACIDIFICATION - Marine Pollution: What Everyone Needs to Know - page 174

Decreased pH reduces the saturation of calcium carbonate,
making it more difficult for some organisms to accumulate
calcium and carbonate to make their hard shells and skel-
etons. Two common mineral forms of calcium carbonate are
aragonite and calcite. Those animals that use aragonite (cor-
als, pteropods, and bivalves) are expected to be more severely
affected than calcite calcifiers (coralline algae, sea urchins)
because of differences in solubility—aragonite is a more sol-
uble mineral form than calcite. (It is interesting to note that
otoliths, the bony structures in fish ears, appear to get larger
in acidified conditions rather than smaller as would be pre-
dicted.) It appears that larval mollusks and some other calci-
fying organisms are already experiencing harmful effects on
shell formation at some locations. Delicate corals may face an
even greater risk because they require very high levels of car-
bonate to build their skeletons. Acidity slows reef-building,
which could lower the resiliency of corals and lead to ero-
sion. Since coral reefs are home to a host of other organisms,
their loss would have extensive effects throughout the marine

Ocean Acidification

1

Atmospheric
carbon dioxide
CO 2

Less acidic more acidic

3

2

Hydrogen
lons

Dissolved
carbon dioxide

Carbonic
Acid

Water

H + H 2 CO 3

CO 2 H 2 O

Bicarbonate
lons

Carbonate
lons

HCO -1 Intact shells

CO -2

Deformed shells

Figure 9.2 Ocean Acidification (taken from Chesapeake Quarterly, Maryland Sea Grant
College Program)