IB BIOLOGY HL Coral reefs and carbon dioxide

2. • Marine animal such as reef-building corals
that deposit calcium carbonate in their
skeletons need to absorb carbonate ions from
seawater.

3. • The concentration of carbonate ions in
seawater is low, because they are not very
soluble.
• Dissolve carbon dioxide makes the carbonate
concentration even lower as a results of some
interrelated chemical reactions.

4. • Carbon dioxide reacts with water to form
carbonic acid, which dissociates into hydrogen
and hydrogen carbonate ions.
• CO2 + H2O  H2CO3  H+ + HCO3-
• Hydrogen ions react with dissolve carbonate
ions, reducing their concentration.
• H+ + CO3
2-  HCO3
-

5. • If carbonate ions concentration drop, it is
more difficult for reef- building corals to
absorb them to make their skeletons.
• If seawater stop to be a saturated solution of
carbonate ions, existing calcium carbonate
tends to dissolve.
• So existing skeletons of reef-building corals are
threatened.

6. • In the area of acidified water, there are no
corals, sea urchins or other animals that make
their skeletons from calcium carbonate.
Sea urchins Corals

7. • In their place, other organisms flourish such as
sea grasses and invasive algae.
Sea grasses
Invasive algae