16
Reef Lime Constructions
the buttress systems preserve communities of the outer reef slope from
destruction (Shinn 1963). The same function is accomplished also by
knolls, which often grow up in this zone (Roberts et al. 1975). The spoors
are places of luxurious coral growth. The coral communities here are of
high species diversity with ramose scleractinians and various
gorgonaceans dominating.
e) Mi - Mixed zone, depth 8-6m. This zone was described by Goreau
and Goreau (1973) as an intermediate between moat and buttress zones.
The zone is characterized by rich coral growth in conditions of significant
wave stress.
£) Mo - Zone of frontal moat, depth 6-4m. The moat, 1-2m deep,
usually extends along the outer reef edge, and is formed through
inhibition of coral growth under the influence of sediment and rubble
shed from the reef flat by tidal currents and surf. Its bottom is usually
covered with rough sand and rubble, overgrown with periphyton. It is
populated by abundant vagile benthos and by solitary corals Fungia.
g) Br - Braker zone, depth 0-2 m. This represents the reef edge,
subjected to maximal wave action. On Atlantic reefs this zone is usually
colonized by massive corals, while on the Indo-Pacific by crustose
coralline algae.
2. Zones of windward reef-flat
a) Ar - Algal ridge zone. The zone is represented by slightly sloping
ridges 10-30 cm high, built up by coralline algae along the windward reef
edges at elevated flats of some old atolls in the Indo-Pacific, and are
situated in the Trade Wind Zone experiencing permanent wave stress.
The same waves repel from this zone fish which graze on coralline algae,
thus stimulating growth and formation of the ridge in this zone (Adey
and Vassar 1975).
b) Bo - Zone of boulder ramparts. The ramparts are the ridges of
calcareous boulders formed from coral colonies consolidated by coralline
algae. The ridges are cut by deep trenches and channels through which
the transport of sediments from the reef flat passes. Behind the boulders
stripes of accumulated rubble and sand (the gravel tail) are situated,
which form cays behind ramparts.
c) Fl - Inner reef flat zone. This is a planar consolidated reef plateau.
Its construction and cover differ on different reefs depending on its
disposition in relation to sea level and on the height of the tides. At
elevated reefs, where flats are exposed during ebb-tides, cays of gravel
are forming along their surface. It is cut by channels and covered mostly
by coralline algae and by small rare coral colonies, which grew in
channels and in depressions. The surface of the flat, exposed only
partially during low water, is usually covered by thickets of macrophytes,
opportunistic ramose corals which survive exposure, siltation and physical
stress (Maxwell 1968), by zoantharians and by ramose coralline algae. On
Reef Lime Constructions
the buttress systems preserve communities of the outer reef slope from
destruction (Shinn 1963). The same function is accomplished also by
knolls, which often grow up in this zone (Roberts et al. 1975). The spoors
are places of luxurious coral growth. The coral communities here are of
high species diversity with ramose scleractinians and various
gorgonaceans dominating.
e) Mi - Mixed zone, depth 8-6m. This zone was described by Goreau
and Goreau (1973) as an intermediate between moat and buttress zones.
The zone is characterized by rich coral growth in conditions of significant
wave stress.
£) Mo - Zone of frontal moat, depth 6-4m. The moat, 1-2m deep,
usually extends along the outer reef edge, and is formed through
inhibition of coral growth under the influence of sediment and rubble
shed from the reef flat by tidal currents and surf. Its bottom is usually
covered with rough sand and rubble, overgrown with periphyton. It is
populated by abundant vagile benthos and by solitary corals Fungia.
g) Br - Braker zone, depth 0-2 m. This represents the reef edge,
subjected to maximal wave action. On Atlantic reefs this zone is usually
colonized by massive corals, while on the Indo-Pacific by crustose
coralline algae.
2. Zones of windward reef-flat
a) Ar - Algal ridge zone. The zone is represented by slightly sloping
ridges 10-30 cm high, built up by coralline algae along the windward reef
edges at elevated flats of some old atolls in the Indo-Pacific, and are
situated in the Trade Wind Zone experiencing permanent wave stress.
The same waves repel from this zone fish which graze on coralline algae,
thus stimulating growth and formation of the ridge in this zone (Adey
and Vassar 1975).
b) Bo - Zone of boulder ramparts. The ramparts are the ridges of
calcareous boulders formed from coral colonies consolidated by coralline
algae. The ridges are cut by deep trenches and channels through which
the transport of sediments from the reef flat passes. Behind the boulders
stripes of accumulated rubble and sand (the gravel tail) are situated,
which form cays behind ramparts.
c) Fl - Inner reef flat zone. This is a planar consolidated reef plateau.
Its construction and cover differ on different reefs depending on its
disposition in relation to sea level and on the height of the tides. At
elevated reefs, where flats are exposed during ebb-tides, cays of gravel
are forming along their surface. It is cut by channels and covered mostly
by coralline algae and by small rare coral colonies, which grew in
channels and in depressions. The surface of the flat, exposed only
partially during low water, is usually covered by thickets of macrophytes,
opportunistic ramose corals which survive exposure, siltation and physical
stress (Maxwell 1968), by zoantharians and by ramose coralline algae. On