It levels could potentially drop below those required to

It can be said that there is
a consensus in scientific knowledge that ocean acidification already having
high impacts on many ocean species and ecosystems.1 Many
marine photosynthetic organisms and animals, such as molluscs, corals,
echinoderms, foraminifera and calcareous algae, make shells and plates out of
calcium carbonate.2 It could happened when the seawater contains a
sufficient concentration of calcium carbonate. Increased concentrations of CO2 will increase acidity which impedes the process of
calcification. Calcifying organisms will be negatively affected in the present
century, with estimates suggesting that calcification rates will decrease by as
much as 50 percent by 2100 due to the fall in calcium carbonate concentration.3

Calcium carbonate is employed as a
construction material for organisms in several crystalline forms, such as
aragonite and calcite. All calcifying organisms are likely to be adversely
affected by ocean acidification, but those that use aragonite will be affected
first as aragonite dissolves more readily due to its crystalline structure.4 At most risk are coral organisms that require aragonite to be
deposited in excess of erosion to build coral reefs and if oceanic pH falls by as much as 0.4 pH units by 2100,
carbonate levels could potentially drop below those required to sustain coral
reef accretion by 2050.5

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1 See, G. De’ath et al.,
“Declining coral calcification on the Great Barrier Reef”, 323 Science (2009),
116.  

2 Royal Society, Ocean
acidification due to increasing atmospheric carbon dioxide (2005), in Rachel Baird, op cit, 5.

3 OSPAR Commission, Effects on the marine environment of ocean
acidification resulting from elevated levels of CO2 in the
atmosphere (2006).  See also, M.
Sakashita, “Petition to regulate carbon dioxide pollution under the Federal
Clean Water Act”, 2007  

4 WGBU, Special Report 2006: The future oceans, warming up, rising
high, turning sour (2006)  

5 W. Burns, “Anthropogenic carbon dioxide emissions and ocean
acidification”, in R.A. Askins et al. (eds), Saving Biological Diversity (Berlin:
Springer, 2008), 187. See also, Hoegh-Guldberg, loc cit.