44
Reef Environments
difference in to even at depths of 40-60 m does not exceed 1-2° and even
this change starts from depths of 20-30m downwards. Some decrease of to
of the deep lagoonal waters is caused by the inflow of the deeper cold water
during the tide (Andrews 1983b).
The lime reef constructions are subjected to powerful hydrodynamic
stress, which partially destroys them and enhances the processes of erosion.
But in its interactions with the reef this physical stress also stimulates many
important biological processes, induces the development of defence
reactions in reefal flora and fauna. These reactions of the biota finally result
in compensation of the physical damage caused by hydrodynamic stress to
the reef, thus providing and even enhancing its growth and morphogenesis
(Heckel 1974). Among such compensative reactions are the acceleration of
coral growth in reefal zones with active hydrodynamics - on buttresses, on
the fore-reef, and at the outer windward reef slope (Wells 1957; Gareau and
Goreau 1973; Roberts et al. 1975). Extensive hydrodynaimcs and high
transparency of the waters over the outer slope provide better conditions for
autotrophic and heterotrophic feeding of corals and a decrease in their
siltation. Being adapted to the wave and currents stress corals form in these
zones dense communities. A rich coral growth stimulates the growth of the
reef body on the outer slope and especially the growth of buttresses - one of
the key geomorphological structures of the reef. Wave stress and the
elevation of sea level up the frontal reef edge are the main factors
instrumental in the development of algal ridges constructed by the coralline
algae (cf. Sect. 1.1). The wave stress up the ridge keep out fish and urchins,
which feed on coralline algae, thus preventing their grazing. It is the
elevated sea level up the reef edge which permits algae to construct the
elevated ridge along it. Being cross-cut by channels, the ridge dissipates
the wave energy and thus preserves the corals that grow on the submerged
flat from destruction.
Under the influence of the wave stress and currents a sorting out and
redistribution of the carbonate material occur (Maxwell 1968; Gallagher et
al. 1971; Roberts et al. 1975; Smith 1973; P.l. Davies 1977). Most important
in these processes are the pulses of currents with a velocity of 1-2 m s -1,
generated by waves on the reef flat with a periodicity of 3-5 s (cf. Fig. 2.3).
These powerful pulsing currents transport the rubble, collect it in ridges had
heaps. By flushing them the currents prevent their being covered by soft
sediments. In these conditions the rubble is quickly consolidated by sponges
and by calcareous algae which fix it onto the flat surface, thus providing for
the growth of the reef body. In submerged parts of the reef flat on the
consolidated rubble material starts the growth of corals. These processes
compensate for the erosion and destruction of reef at sites of extensive
hydrodynamic stress (Marshall 1968).
Active hydrodynamics on coral reefs is one of the most important factors
ensuring their high productivity. The interaction of reefs with the oceanic
currents, as well as the tidal and the barotrophic long-period oscillations of
Reef Environments
difference in to even at depths of 40-60 m does not exceed 1-2° and even
this change starts from depths of 20-30m downwards. Some decrease of to
of the deep lagoonal waters is caused by the inflow of the deeper cold water
during the tide (Andrews 1983b).
The lime reef constructions are subjected to powerful hydrodynamic
stress, which partially destroys them and enhances the processes of erosion.
But in its interactions with the reef this physical stress also stimulates many
important biological processes, induces the development of defence
reactions in reefal flora and fauna. These reactions of the biota finally result
in compensation of the physical damage caused by hydrodynamic stress to
the reef, thus providing and even enhancing its growth and morphogenesis
(Heckel 1974). Among such compensative reactions are the acceleration of
coral growth in reefal zones with active hydrodynamics - on buttresses, on
the fore-reef, and at the outer windward reef slope (Wells 1957; Gareau and
Goreau 1973; Roberts et al. 1975). Extensive hydrodynaimcs and high
transparency of the waters over the outer slope provide better conditions for
autotrophic and heterotrophic feeding of corals and a decrease in their
siltation. Being adapted to the wave and currents stress corals form in these
zones dense communities. A rich coral growth stimulates the growth of the
reef body on the outer slope and especially the growth of buttresses - one of
the key geomorphological structures of the reef. Wave stress and the
elevation of sea level up the frontal reef edge are the main factors
instrumental in the development of algal ridges constructed by the coralline
algae (cf. Sect. 1.1). The wave stress up the ridge keep out fish and urchins,
which feed on coralline algae, thus preventing their grazing. It is the
elevated sea level up the reef edge which permits algae to construct the
elevated ridge along it. Being cross-cut by channels, the ridge dissipates
the wave energy and thus preserves the corals that grow on the submerged
flat from destruction.
Under the influence of the wave stress and currents a sorting out and
redistribution of the carbonate material occur (Maxwell 1968; Gallagher et
al. 1971; Roberts et al. 1975; Smith 1973; P.l. Davies 1977). Most important
in these processes are the pulses of currents with a velocity of 1-2 m s -1,
generated by waves on the reef flat with a periodicity of 3-5 s (cf. Fig. 2.3).
These powerful pulsing currents transport the rubble, collect it in ridges had
heaps. By flushing them the currents prevent their being covered by soft
sediments. In these conditions the rubble is quickly consolidated by sponges
and by calcareous algae which fix it onto the flat surface, thus providing for
the growth of the reef body. In submerged parts of the reef flat on the
consolidated rubble material starts the growth of corals. These processes
compensate for the erosion and destruction of reef at sites of extensive
hydrodynamic stress (Marshall 1968).
Active hydrodynamics on coral reefs is one of the most important factors
ensuring their high productivity. The interaction of reefs with the oceanic
currents, as well as the tidal and the barotrophic long-period oscillations of