FOREREEF/REEF FRONT
Guy Cabioch
Institut de Recherche pour le Développement, Bondy,
CEDEX, France
Synonyms
Outer reef margin; Outer reef slope; Reef face; Reef slope
Definition
The forereef is the outside part of a reef seaward of the reef
crest (or reef edge) facing open sea.
Morphology
The forereef is characterized by peculiar morpholological
features (Guilcher, 1988; Hopley et al., 2007). The most
common feature is the inclination of the slope marked by
some breaks and sometimes the occurrence of more or less
flat terraces or platforms. The forereef is also characterized by the occurrence of spur and groove system in the
upper parts, and sometimes by landslides or slipped
blocks. Drowned reefs can be unusual morphological
features observed in some forereefs. The forereef can be
distributed into shallower and deeper zones.
Factors controlling the morphology
The morphology of the forereef slopes depends on both
climatic and tectonic variations and is controlled by several factors including the following (non exhaustive list):
(1) the inheritance of morphology (ancient reefs formed
during the past sea level variations) (2) the antecedent
morphology depending on subaerial exposure and alteration (karstification) during the low stands of sea level;
(3) processes of cementation; (4) biological activity taking
into account the competition between the various organisms and depending on the degree of water energy
and irradiance; (5) collapse and slides resulting from
storms, hurricanes, seismic events, or tsunamis; (6) the
bioerosion; and (7) the interaction of currents.
Biozonation
The upper parts of the forereef slope are exposed to the
strong wave energy and are characterized by the algal crest
in the Indo-Pacific region and by spurs and grooves
extending downward. Many boulders and various debris
materials can be found. The living corals are generally
abundant. In the Caribbean, six types of breaker zones
(upper parts of the forereef ) were defined depending on
the degree of energy of wave exposure (Geister, 1977)
displaying some regional variations.
The deeper parts of the forereef slope are generally
poorly investigated and consequently little is known from
this zone. This area can be marked by steep slope as
observed in French Polynesia (Montaggioni et al., 1987)
and is characterized by the low degree of water energy
and irradiance. Some submersible observations were
performed along the forereef slopes as for example in
Jamaica (Land and Moore, 1977) and in Belize (James
and Ginsburg, 1979) in the Caribbean, and in Tahiti
(Salvat et al., 1985) in the Pacific, where some morphological features were recognized as submerged terraces
or series of steps or blocks falling from the above modern
coral reefs.
Biological encrusting zonation
A recent study performed in New Caledonia (Flamand
et al., 2008) revealed the occurrence of several biofacies
along the forereef comprising mainly bindstones dominated by coralline algal and/or foraminiferal crusts. Based
on these observations and taking into account the distribution and abundance of the coralline algae and acervulinid
foraminifera depending on the degree of water energy
and irradiance, a model of bathymetric range of encrusting
organisms was proposed. The coralline algae rich in
mastophorids and/or lithophylloids are abundant in the
upper parts of the forereef, the coraline algal assemblage
rich in melobesoids, Sporolithon sp., and Peyssonnelia
sp. in the deeper parts, and foraminiferal crusts are dominant below 90 m progressively replacing the coralline
algal crusts.
Occurrence of micritic crusts
Laminar micritic crusts were observed in the Red Sea by
Brachert and Dullo (1991) on the ledge-rocks from 120
to 200 m. Such crusts were also observed on the forereefs
from Belize and Jamaica (James and Ginsburg, 1979;
Land and Moore, 1980). In Tahiti, in French Polynesia,
relatively thick crusts recovered from 80 to 130 m were
interpreted as microbialite crusts (Camoin et al., 2006).
Summary
The morphology of forereefs mainly reflects the effects
of reef growth in interaction with the sea level variations
and in combination with the subsidence and uplift movements. Little is known regarding the distribution and the
abundance of organisms especially in the deeper parts.
Nevertheless, the biological assemblages appear to be distributed characteristically with the water depth depending
on the degree of wave energy and irradiance.
Bibliography
Brachert, T. C., and Dullo, W.-C., 1991. Laminar micrite crusts and
associated foreslope processes, Red Sea. Journal of sedimentary
Petrolology, 61, 354–363.
Camoin, G., Cabioch, G., Eisenhauer, A., Braga, J.-C., Hamelin, B.,
and Lericolais, G., 2006. Environmental significance of
microbialites in reef environments during the Last Deglaciation.
Sedimentary Geology, 185, 277–295.
Flamand, B., Cabioch, G., Payri, C. E., and Pelletier, B., 2008.
Nature and biological composition of the New Caledonian outer
barrier reef slopes. Marine Geology, 250, 157–179.
Geister, J., 1977. The influence of wave exposure on the ecological
zonation of Caribbean coral reefs. In Proceedings of the third
International Coral Reef Symposium, Miami, 1, pp. 23–29.
422
FOREREEF/REEF FRONT
Guy Cabioch
Institut de Recherche pour le Développement, Bondy,
CEDEX, France
Synonyms
Outer reef margin; Outer reef slope; Reef face; Reef slope
Definition
The forereef is the outside part of a reef seaward of the reef
crest (or reef edge) facing open sea.
Morphology
The forereef is characterized by peculiar morpholological
features (Guilcher, 1988; Hopley et al., 2007). The most
common feature is the inclination of the slope marked by
some breaks and sometimes the occurrence of more or less
flat terraces or platforms. The forereef is also characterized by the occurrence of spur and groove system in the
upper parts, and sometimes by landslides or slipped
blocks. Drowned reefs can be unusual morphological
features observed in some forereefs. The forereef can be
distributed into shallower and deeper zones.
Factors controlling the morphology
The morphology of the forereef slopes depends on both
climatic and tectonic variations and is controlled by several factors including the following (non exhaustive list):
(1) the inheritance of morphology (ancient reefs formed
during the past sea level variations) (2) the antecedent
morphology depending on subaerial exposure and alteration (karstification) during the low stands of sea level;
(3) processes of cementation; (4) biological activity taking
into account the competition between the various organisms and depending on the degree of water energy
and irradiance; (5) collapse and slides resulting from
storms, hurricanes, seismic events, or tsunamis; (6) the
bioerosion; and (7) the interaction of currents.
Biozonation
The upper parts of the forereef slope are exposed to the
strong wave energy and are characterized by the algal crest
in the Indo-Pacific region and by spurs and grooves
extending downward. Many boulders and various debris
materials can be found. The living corals are generally
abundant. In the Caribbean, six types of breaker zones
(upper parts of the forereef ) were defined depending on
the degree of energy of wave exposure (Geister, 1977)
displaying some regional variations.
The deeper parts of the forereef slope are generally
poorly investigated and consequently little is known from
this zone. This area can be marked by steep slope as
observed in French Polynesia (Montaggioni et al., 1987)
and is characterized by the low degree of water energy
and irradiance. Some submersible observations were
performed along the forereef slopes as for example in
Jamaica (Land and Moore, 1977) and in Belize (James
and Ginsburg, 1979) in the Caribbean, and in Tahiti
(Salvat et al., 1985) in the Pacific, where some morphological features were recognized as submerged terraces
or series of steps or blocks falling from the above modern
coral reefs.
Biological encrusting zonation
A recent study performed in New Caledonia (Flamand
et al., 2008) revealed the occurrence of several biofacies
along the forereef comprising mainly bindstones dominated by coralline algal and/or foraminiferal crusts. Based
on these observations and taking into account the distribution and abundance of the coralline algae and acervulinid
foraminifera depending on the degree of water energy
and irradiance, a model of bathymetric range of encrusting
organisms was proposed. The coralline algae rich in
mastophorids and/or lithophylloids are abundant in the
upper parts of the forereef, the coraline algal assemblage
rich in melobesoids, Sporolithon sp., and Peyssonnelia
sp. in the deeper parts, and foraminiferal crusts are dominant below 90 m progressively replacing the coralline
algal crusts.
Occurrence of micritic crusts
Laminar micritic crusts were observed in the Red Sea by
Brachert and Dullo (1991) on the ledge-rocks from 120
to 200 m. Such crusts were also observed on the forereefs
from Belize and Jamaica (James and Ginsburg, 1979;
Land and Moore, 1980). In Tahiti, in French Polynesia,
relatively thick crusts recovered from 80 to 130 m were
interpreted as microbialite crusts (Camoin et al., 2006).
Summary
The morphology of forereefs mainly reflects the effects
of reef growth in interaction with the sea level variations
and in combination with the subsidence and uplift movements. Little is known regarding the distribution and the
abundance of organisms especially in the deeper parts.
Nevertheless, the biological assemblages appear to be distributed characteristically with the water depth depending
on the degree of wave energy and irradiance.
Bibliography
Brachert, T. C., and Dullo, W.-C., 1991. Laminar micrite crusts and
associated foreslope processes, Red Sea. Journal of sedimentary
Petrolology, 61, 354–363.
Camoin, G., Cabioch, G., Eisenhauer, A., Braga, J.-C., Hamelin, B.,
and Lericolais, G., 2006. Environmental significance of
microbialites in reef environments during the Last Deglaciation.
Sedimentary Geology, 185, 277–295.
Flamand, B., Cabioch, G., Payri, C. E., and Pelletier, B., 2008.
Nature and biological composition of the New Caledonian outer
barrier reef slopes. Marine Geology, 250, 157–179.
Geister, J., 1977. The influence of wave exposure on the ecological
zonation of Caribbean coral reefs. In Proceedings of the third
International Coral Reef Symposium, Miami, 1, pp. 23–29.
422
FOREREEF/REEF FRONT