producers, and the destructive processes of mechanical
wave action and bioerosion (e.g., Darwin, 1842; Scoffin,
1992). Initially, the recognition of these dynamics
underpinned explanations of the presence and gross structure of coral reefs and they have been modeled using
a carbonate budget approach (Perry and Hepburn, 2008;
Perry et al., 2008). The by-products of reef growth and
destruction (detrital sediment) can also lead to landform
construction and change. For instance, reef islands rely
on production and transfer of detrital sediment from
a contiguous reef system, although they have typically
been regarded as losses to the reef sediment budget
(Scoffin et al., 1980; Hubbard et al., 1990; Kleypas
et al., 2001). Over the past century, an expansion of
research to describe and account for other morphological
features on and adjacent to coral reef structures has recognized that the balance of constructive and destructive processes on reefs operates at a range of space and time
scales. Variability in that balance (e.g., in extent, rates,
duration, timing) produces a wide range of macro- to
micro-scale geomorphic units, from entire reef platforms
to a particular spur and groove morphology.
Physical processes that mechanically erode, transport,
and deposit calcium carbonate are of paramount importance
in controlling the distribution, structure, and morphology
of reefs and sedimentary landforms (Scoffin et al., 1980).
Once a reef is constructed, feedbacks that modify microenvironments and process interactions that drive the distribution of ecological communities and morphological products
exist. The term “eco-morphodynamics” was recently introduced by Kench et al. (2009) as a conceptual framework
to provide a more detailed exploration of the complex
relationships that exist between ecological and physical
processes and reef geomorphology.
Morphodynamic origins
Eco-morphodynamics is an extension of the
morphodynamic concept, which has been widely used
by geomorphologists to account for the co-adjustment of
landforms and processes in coastal environments (Wright
and Thom, 1977; Cowell and Thom, 1994). Typically
applied in siliciclastic coastal settings, a morphodynamic
approach accounts for hydrodynamic processes and their
interaction with seafloor and coastal features to drive morphological adjustment involving the movement of sediment. Hydrodynamic processes include waves, tides, and
wind-induced currents. While these processes respond
instantaneously to morphology, morphological change
itself is slower, requiring the redistribution of sediment.
As sediment takes a finite time to move, there is a lag in
the morphological response to hydrodynamic forcing.
Therefore, sediment can be considered to be a timedependent coupling mechanism. Unique to coral reef
systems, the sediment reservoir is produced solely by ecological processes that produce calcium carbonate. Furthermore, different coral reef settings (locations; geomorphic
zones) vary greatly in the rates at which they produce calcium carbonate (Kinsey, 1983). Consequently, the carbonate factory is a highly space- and time-dependent coupling
mechanism. However, the time dependency of reef geomorphology to the carbonate factory emerges not only
from the temporal lags in redistribution of material but also
from the timeframes associated with organism growth,
mortality, and conversion to detrital sediment (Perry
et al., 2008). The influence of such temporal lags on morphological change in reef systems is poorly understood.
Eco-morphodynamic framework
The structure and function of the eco-morphodynamic
framework of a coral reef system is presented in Figure 1,
which clearly shows the importance of carbonate cycling.
Examination of this framework highlights a number of
implications for the co-adjustment of physical processes,
reef ecological communities, and geomorphic products.
Boundary controls
Alterations in boundary controls will force change in coral
reef system state (ecological, physical, and geological
characteristics). Such changes in boundary conditions
can occur as a consequence of extrinsic changes in the
atmosphere–ocean system such as sea-level rise, ocean
temperature, and chemistry variations (Hoegh-Guldberg,
1999; Kleypas et al., 2001; Buddemeier et al., 2004; Orr
et al., 2005; Kench et al., 2009). Changes in the intrinsic
factors (e.g., physical and ecological processes) can also
force dynamic change in reef systems. These intrinsic
linkages are themselves impacted by anthropogenic activities such as over-exploitation of physical and biological
resources and coastal construction (Browne and Dunne,
1988; Jackson, 2001; Hughes et al., 2003; Lidz and
Hallock, 2000; Sheppard et al., 2005).
Time and space scales of change
The magnitude, mode, and timeframes of change (responsiveness) in the system are likely to vary considerably
between different components of a reef system. Examples
include the following:
(i) Development of coral reef platforms, which are
known to be modulated by sea-level oscillations at
millennial timescales (Kennedy and Woodroffe,
2002; Montaggioni, 2005)
(ii) Reef island development, which is a function of a reef
basement, sediment supply, and process regime,
occurring at centennial timescales (Woodroffe,
2003; Kench et al., 2005)
(iii) Shoreline dynamics of reef islands, which occur at
event to decadal timescales in response to alterations
in wave energy input (Maragos et al., 1973; Flood,
1986; Kench and Brander, 2006a)
(iv) Ecological transitions that can occur at event to
decadal timeframes in response to extreme climatic
events or changes in ocean temperature, ocean
360
ECO-MORPHODYNAMICS
wave action and bioerosion (e.g., Darwin, 1842; Scoffin,
1992). Initially, the recognition of these dynamics
underpinned explanations of the presence and gross structure of coral reefs and they have been modeled using
a carbonate budget approach (Perry and Hepburn, 2008;
Perry et al., 2008). The by-products of reef growth and
destruction (detrital sediment) can also lead to landform
construction and change. For instance, reef islands rely
on production and transfer of detrital sediment from
a contiguous reef system, although they have typically
been regarded as losses to the reef sediment budget
(Scoffin et al., 1980; Hubbard et al., 1990; Kleypas
et al., 2001). Over the past century, an expansion of
research to describe and account for other morphological
features on and adjacent to coral reef structures has recognized that the balance of constructive and destructive processes on reefs operates at a range of space and time
scales. Variability in that balance (e.g., in extent, rates,
duration, timing) produces a wide range of macro- to
micro-scale geomorphic units, from entire reef platforms
to a particular spur and groove morphology.
Physical processes that mechanically erode, transport,
and deposit calcium carbonate are of paramount importance
in controlling the distribution, structure, and morphology
of reefs and sedimentary landforms (Scoffin et al., 1980).
Once a reef is constructed, feedbacks that modify microenvironments and process interactions that drive the distribution of ecological communities and morphological products
exist. The term “eco-morphodynamics” was recently introduced by Kench et al. (2009) as a conceptual framework
to provide a more detailed exploration of the complex
relationships that exist between ecological and physical
processes and reef geomorphology.
Morphodynamic origins
Eco-morphodynamics is an extension of the
morphodynamic concept, which has been widely used
by geomorphologists to account for the co-adjustment of
landforms and processes in coastal environments (Wright
and Thom, 1977; Cowell and Thom, 1994). Typically
applied in siliciclastic coastal settings, a morphodynamic
approach accounts for hydrodynamic processes and their
interaction with seafloor and coastal features to drive morphological adjustment involving the movement of sediment. Hydrodynamic processes include waves, tides, and
wind-induced currents. While these processes respond
instantaneously to morphology, morphological change
itself is slower, requiring the redistribution of sediment.
As sediment takes a finite time to move, there is a lag in
the morphological response to hydrodynamic forcing.
Therefore, sediment can be considered to be a timedependent coupling mechanism. Unique to coral reef
systems, the sediment reservoir is produced solely by ecological processes that produce calcium carbonate. Furthermore, different coral reef settings (locations; geomorphic
zones) vary greatly in the rates at which they produce calcium carbonate (Kinsey, 1983). Consequently, the carbonate factory is a highly space- and time-dependent coupling
mechanism. However, the time dependency of reef geomorphology to the carbonate factory emerges not only
from the temporal lags in redistribution of material but also
from the timeframes associated with organism growth,
mortality, and conversion to detrital sediment (Perry
et al., 2008). The influence of such temporal lags on morphological change in reef systems is poorly understood.
Eco-morphodynamic framework
The structure and function of the eco-morphodynamic
framework of a coral reef system is presented in Figure 1,
which clearly shows the importance of carbonate cycling.
Examination of this framework highlights a number of
implications for the co-adjustment of physical processes,
reef ecological communities, and geomorphic products.
Boundary controls
Alterations in boundary controls will force change in coral
reef system state (ecological, physical, and geological
characteristics). Such changes in boundary conditions
can occur as a consequence of extrinsic changes in the
atmosphere–ocean system such as sea-level rise, ocean
temperature, and chemistry variations (Hoegh-Guldberg,
1999; Kleypas et al., 2001; Buddemeier et al., 2004; Orr
et al., 2005; Kench et al., 2009). Changes in the intrinsic
factors (e.g., physical and ecological processes) can also
force dynamic change in reef systems. These intrinsic
linkages are themselves impacted by anthropogenic activities such as over-exploitation of physical and biological
resources and coastal construction (Browne and Dunne,
1988; Jackson, 2001; Hughes et al., 2003; Lidz and
Hallock, 2000; Sheppard et al., 2005).
Time and space scales of change
The magnitude, mode, and timeframes of change (responsiveness) in the system are likely to vary considerably
between different components of a reef system. Examples
include the following:
(i) Development of coral reef platforms, which are
known to be modulated by sea-level oscillations at
millennial timescales (Kennedy and Woodroffe,
2002; Montaggioni, 2005)
(ii) Reef island development, which is a function of a reef
basement, sediment supply, and process regime,
occurring at centennial timescales (Woodroffe,
2003; Kench et al., 2005)
(iii) Shoreline dynamics of reef islands, which occur at
event to decadal timescales in response to alterations
in wave energy input (Maragos et al., 1973; Flood,
1986; Kench and Brander, 2006a)
(iv) Ecological transitions that can occur at event to
decadal timeframes in response to extreme climatic
events or changes in ocean temperature, ocean
360
ECO-MORPHODYNAMICS