construction. Carbonate is also added to a reef’s structure by
calcareous algae and other calcareous encrusting organisms,
through carbonate sedimentation, and by the precipitation of
marine cements. Alongside these constructive processes,
a range of physical and biological processes also operate to
directly erode the accumulating reef structure. This eroded
carbonate may subsequently re-accumulate within the reef
structure or be exported out of the reef system. Summing
the rates at which these different carbonate producing and
eroding processes operate, thus allows the net rate of carbonate production on a reef to be quantified. A carbonate budget
is thus a summation of the inputs and outputs of carbonate
within the active carbonate producing environment and is
typically expressed as a measure in kg CaCO 3 m
À2 year
À1
.
Carbonate budget assessments, although logistically complex to construct, thus provide a useful estimation of net carbonate production rates on a reef at a given point in time.
They also provide a mechanism for quantifying the relative
importance of different carbonate producing and eroding
processes, and provide an important insight into inter-reef
variations in styles and rates of reef framework development. This has relevance to understanding both variability
in the composition of accumulating reef framework structures and actual rates of framework accumulation.
Quantifying reef framework production and cycling
Coral reefs and reef sedimentary landforms are unique in
that they are composed predominantly of calcium carbonate (CaCO 3 ) that results almost entirely from ecological
processes. Corals typically represent the primary constructional components on most reefs and can add significant amounts of carbonate per unit area of reef surface
(Vecsei, 2004). However, other carbonate producing processes also add additional CaCO 3 to the reef framework,
the most important being by calcareous encrusters (especially crustose coralline algae), and the precipitation of
syn- and early post-depositional cements (Perry and
Hepburn, 2008). Significant amounts of primary carbonate are also produced in the form of sediment by other
organisms or plants that induce CaCO 3 deposition. These
additional sources of carbonate can contribute significant
quantities of carbonate to the reef structure and may actually dominate CaCO 3 accumulation in specific reef settings (Bosence, 1984; Camoin et al., 2006).
A range of physical and biological erosional processes
also influence rates and styles of reef framework accumulation. Bioerosion (the biological erosion of carbonate
substrates) is facilitated by a wide range of reef-associated
faunas, including species of fish and echinoids, and endolithic forms of sponges, bivalves and worms (see
Chapter Bioerosion). These biological agents drive the
direct degradation of both primary and secondary reef
framework constituents and, as a by-product, may produce
large amounts of sediment (Scoffin et al., 1980;
Bruggemann et al., 1996). Physical disturbance, associated
with storms and cyclones, is an important episodic process
that influences reef framework development, largely
through the generation of coral rubble, the deposition of
which is an important reef-building process in its own right
(Hubbard, 1997; Blanchon et al., 1997), and through the
export of reef-derived sediments (Hubbard et al., 1990).
These various carbonate producing and cycling processes may thus exert either a “constructive” or “destructive” (sensu Scoffin, 1992) influence on reef-related
carbonate accumulation, and the relative importance of
each, within a given reef system, controls net rates of carbonate accumulation. This concept is defined by the carbonate budget approach to conceptualizing and
quantifying reef geomorphic performance and can be
viewed as the sum of gross carbonate production from
corals and calcareous encrusters, as well as sediment produced within or imported into the reef, less that lost
through biological or physical erosion, dissolution or sediment export (Figure 1). The balance between these different inputs and outputs represents the net production rate of
framework CaCO 3 and can be expressed as:
Net rate of framework CaCO 3 production =
[(P pf þ P sf ) À P e ] þ Sed i
where
P pf = Primary framework carbonate production.
P sf = Secondary framework carbonate production.
P e = Primary and secondary framework carbonate lost to
erosion.
Sed i = Sediment incorporated into the reef framework
(includes both benthic carbonate sediment and by-products of framework erosion less that exported from the
reef).
Several detailed studies have quantified net rates of carbonate production, using carbonate budgets approaches, at the
reef system scale, and these including studies on Caribbean
reefs in Barbados (4.48 kg CaCO 3 m
À2 yr
À1
; Scoffin et al.,
1980) and St. Croix (0.91 kg CaCO 3 m
À2 yr
À1
; Hubbard
et al., 1990), and in the Indo Pacific in Hawaii (0.89 kg
CaCO 3 m
À2 yr
À1
; Harney and Fletcher, 2003) and Indonesia (ranging from 11.68 to À7.6 kg CaCO 3 m
À2 yr
À1
;
Edinger et al., 2000). Several studies have also utilized census-based budget approaches to quantify rates of sediment
production within reef-related sedimentary environments.
These include estimates of reef island sediment production
(Hart and Kench, 2007), and epiphytic carbonate production in seagrass beds (Nelson and Ginsburg, 1986; Perry
and Beavington-Penney, 2005). It is relevant to note that
rates of carbonate production on shallow-water reefs have
also previously been estimated using measures of alkalinity
change in the waters overlying reefs (see Chapter Density
and Porosity: Influence on Reef Accretion Rates). This
approach provides an estimation of total carbonate production and early dissolution (Smith and Kinsey, 1976), and
while resultant production estimates are in broad accord
with the gross production estimates determined in process
or census-based studies, it is not possible to quantify the
production and erosion rates associated with individual
organisms and/or processes. The approach thus has
186
CARBONATE BUDGETS AND REEF FRAMEWORK ACCUMULATION
calcareous algae and other calcareous encrusting organisms,
through carbonate sedimentation, and by the precipitation of
marine cements. Alongside these constructive processes,
a range of physical and biological processes also operate to
directly erode the accumulating reef structure. This eroded
carbonate may subsequently re-accumulate within the reef
structure or be exported out of the reef system. Summing
the rates at which these different carbonate producing and
eroding processes operate, thus allows the net rate of carbonate production on a reef to be quantified. A carbonate budget
is thus a summation of the inputs and outputs of carbonate
within the active carbonate producing environment and is
typically expressed as a measure in kg CaCO 3 m
À2 year
À1
.
Carbonate budget assessments, although logistically complex to construct, thus provide a useful estimation of net carbonate production rates on a reef at a given point in time.
They also provide a mechanism for quantifying the relative
importance of different carbonate producing and eroding
processes, and provide an important insight into inter-reef
variations in styles and rates of reef framework development. This has relevance to understanding both variability
in the composition of accumulating reef framework structures and actual rates of framework accumulation.
Quantifying reef framework production and cycling
Coral reefs and reef sedimentary landforms are unique in
that they are composed predominantly of calcium carbonate (CaCO 3 ) that results almost entirely from ecological
processes. Corals typically represent the primary constructional components on most reefs and can add significant amounts of carbonate per unit area of reef surface
(Vecsei, 2004). However, other carbonate producing processes also add additional CaCO 3 to the reef framework,
the most important being by calcareous encrusters (especially crustose coralline algae), and the precipitation of
syn- and early post-depositional cements (Perry and
Hepburn, 2008). Significant amounts of primary carbonate are also produced in the form of sediment by other
organisms or plants that induce CaCO 3 deposition. These
additional sources of carbonate can contribute significant
quantities of carbonate to the reef structure and may actually dominate CaCO 3 accumulation in specific reef settings (Bosence, 1984; Camoin et al., 2006).
A range of physical and biological erosional processes
also influence rates and styles of reef framework accumulation. Bioerosion (the biological erosion of carbonate
substrates) is facilitated by a wide range of reef-associated
faunas, including species of fish and echinoids, and endolithic forms of sponges, bivalves and worms (see
Chapter Bioerosion). These biological agents drive the
direct degradation of both primary and secondary reef
framework constituents and, as a by-product, may produce
large amounts of sediment (Scoffin et al., 1980;
Bruggemann et al., 1996). Physical disturbance, associated
with storms and cyclones, is an important episodic process
that influences reef framework development, largely
through the generation of coral rubble, the deposition of
which is an important reef-building process in its own right
(Hubbard, 1997; Blanchon et al., 1997), and through the
export of reef-derived sediments (Hubbard et al., 1990).
These various carbonate producing and cycling processes may thus exert either a “constructive” or “destructive” (sensu Scoffin, 1992) influence on reef-related
carbonate accumulation, and the relative importance of
each, within a given reef system, controls net rates of carbonate accumulation. This concept is defined by the carbonate budget approach to conceptualizing and
quantifying reef geomorphic performance and can be
viewed as the sum of gross carbonate production from
corals and calcareous encrusters, as well as sediment produced within or imported into the reef, less that lost
through biological or physical erosion, dissolution or sediment export (Figure 1). The balance between these different inputs and outputs represents the net production rate of
framework CaCO 3 and can be expressed as:
Net rate of framework CaCO 3 production =
[(P pf þ P sf ) À P e ] þ Sed i
where
P pf = Primary framework carbonate production.
P sf = Secondary framework carbonate production.
P e = Primary and secondary framework carbonate lost to
erosion.
Sed i = Sediment incorporated into the reef framework
(includes both benthic carbonate sediment and by-products of framework erosion less that exported from the
reef).
Several detailed studies have quantified net rates of carbonate production, using carbonate budgets approaches, at the
reef system scale, and these including studies on Caribbean
reefs in Barbados (4.48 kg CaCO 3 m
À2 yr
À1
; Scoffin et al.,
1980) and St. Croix (0.91 kg CaCO 3 m
À2 yr
À1
; Hubbard
et al., 1990), and in the Indo Pacific in Hawaii (0.89 kg
CaCO 3 m
À2 yr
À1
; Harney and Fletcher, 2003) and Indonesia (ranging from 11.68 to À7.6 kg CaCO 3 m
À2 yr
À1
;
Edinger et al., 2000). Several studies have also utilized census-based budget approaches to quantify rates of sediment
production within reef-related sedimentary environments.
These include estimates of reef island sediment production
(Hart and Kench, 2007), and epiphytic carbonate production in seagrass beds (Nelson and Ginsburg, 1986; Perry
and Beavington-Penney, 2005). It is relevant to note that
rates of carbonate production on shallow-water reefs have
also previously been estimated using measures of alkalinity
change in the waters overlying reefs (see Chapter Density
and Porosity: Influence on Reef Accretion Rates). This
approach provides an estimation of total carbonate production and early dissolution (Smith and Kinsey, 1976), and
while resultant production estimates are in broad accord
with the gross production estimates determined in process
or census-based studies, it is not possible to quantify the
production and erosion rates associated with individual
organisms and/or processes. The approach thus has
186
CARBONATE BUDGETS AND REEF FRAMEWORK ACCUMULATION