74
8. Calcification, Erosion and the
Establishment of the Framework
of Coral Reefs
P. A. Hutchings & O. Hoegh-Guldberg
abundance of these crucial ions as one goes poleward.
This association of calcification with low latitude environments appears to have held for many hundreds of
millions of years, resulting in huge deposits of calcium
carbonate within the Earth’s geological structure.
The organisms that calcify on coral reefs are diverse
and include a large number of phyla including cnidarians, molluscs, crustaceans and foraminifera as well as
green and red algae. Many of the organisms that calcify
at high rates are also symbiotic with dinoflagellates
such as Symbiodinium (see Chapter 7). This association
with organisms having high photosynthetic capabilities
is considered to be indicative of the high energy requirements of the calcification process. These organisms take
up calcium and carbonate ion from the super-saturated
concentrations typical of tropical and subtropical waters,
depositing either calcite or aragonite (two forms of calcium carbonate crystals). The form of calcium carbonate
deposited depends mostly on the organism involved.
Corals, for example, deposit aragonite while red coralline algae deposit Mg-calcite.
Organisms use calcium carbonate to create skeletons that either provide rigid support structures and/
or protective shells or cases. These functions are likely
Much like a city represents an equilibrium between
processes of building construction and demolition, coral
reefs are the net result of processes that form calcium
carbonate (calcification) and those that take it away
(physical and biological erosion). The resulting reef
framework is quintessential to coral reefs, forming the
habitat for tens of thousands of reef species. This chapter
examines the major forces that control this equilibrium
state, examining the physical, chemical and biological
forces that are involved. It also investigates the role that
humans have in influencing these processes, highlighting the large scale effects of both local (eutrophication,
land runoff) and global (global warming, ocean acidification) factors on reef structures. Some of these issues
will also be discussed further in Chapter 10.
N CALCIFICATION
Calcification is highest in the warm, sunlit waters of the
tropics and subtropics where the concentrations of calcium and carbonate ions are highest. As discussed in
Chapter 2, these three factors are considered to be the
major determinants for where coral reefs grow, with
waters becoming the too cold, dim and low in the
8. Calcification, Erosion and the
Establishment of the Framework
of Coral Reefs
P. A. Hutchings & O. Hoegh-Guldberg
abundance of these crucial ions as one goes poleward.
This association of calcification with low latitude environments appears to have held for many hundreds of
millions of years, resulting in huge deposits of calcium
carbonate within the Earth’s geological structure.
The organisms that calcify on coral reefs are diverse
and include a large number of phyla including cnidarians, molluscs, crustaceans and foraminifera as well as
green and red algae. Many of the organisms that calcify
at high rates are also symbiotic with dinoflagellates
such as Symbiodinium (see Chapter 7). This association
with organisms having high photosynthetic capabilities
is considered to be indicative of the high energy requirements of the calcification process. These organisms take
up calcium and carbonate ion from the super-saturated
concentrations typical of tropical and subtropical waters,
depositing either calcite or aragonite (two forms of calcium carbonate crystals). The form of calcium carbonate
deposited depends mostly on the organism involved.
Corals, for example, deposit aragonite while red coralline algae deposit Mg-calcite.
Organisms use calcium carbonate to create skeletons that either provide rigid support structures and/
or protective shells or cases. These functions are likely
Much like a city represents an equilibrium between
processes of building construction and demolition, coral
reefs are the net result of processes that form calcium
carbonate (calcification) and those that take it away
(physical and biological erosion). The resulting reef
framework is quintessential to coral reefs, forming the
habitat for tens of thousands of reef species. This chapter
examines the major forces that control this equilibrium
state, examining the physical, chemical and biological
forces that are involved. It also investigates the role that
humans have in influencing these processes, highlighting the large scale effects of both local (eutrophication,
land runoff) and global (global warming, ocean acidification) factors on reef structures. Some of these issues
will also be discussed further in Chapter 10.
N CALCIFICATION
Calcification is highest in the warm, sunlit waters of the
tropics and subtropics where the concentrations of calcium and carbonate ions are highest. As discussed in
Chapter 2, these three factors are considered to be the
major determinants for where coral reefs grow, with
waters becoming the too cold, dim and low in the