154
Benthic Microftora, Periphyton and Plant Associations
at the windward reef edges and over the algal ridges, being a main reef
builder in this zone of Indo-Pacific reefs. At the Atlantic reefs (Saint Croix,
Virgin Islands) the same turbulent zones are occupied by another crustose
coralline alga, Lithophyllum congestum (Adey 1975). This species is very
similar to P. oncoides in its spectrum of ecological adaptations. Growing on
reef edge, this alga constructs solid knolls, "boylers", exposed during the
ebbs, which in their structure are similar to the algal ridges of Indo-Pacific
atolls. On the algal ridges of numerous algal reefs in the Indian Ocean the
same function is accomplished had by Neogoniolithon frutescens.
Another mass species of Porolithon, P. gardineri, is also largely similar to
P. oncoides in its ecological characteristics, though it is less resistant to
wave-stress. Its colonies are not so monolithic as in P. oncoides, having
protuberances on their surface. The Sporolithon and the Hydrolithon are
adapted to a medium level of illumination and do not endure the strong
surf. They inhabit the shadowed calmer places under corals, under
macrophytes, or in trenches of flatts. These species also could be met with in
biotopes of outer reef slopees at depth of more than 10 m, where the surf
and the light conditions are optimal for them (Littler 1973b; Doty 1974; d.
Fig. 4.4). Coralline algae sustain better also the strong currents which often
happen to flow over the reef flat, and are less damaged by rubble which they
are moving up from the bottom. Therefore, they often replace the fleshy
macrophytes in parts of the flat subjected to strong wave-driven or tidal
currents (Doty 1974). The antropogenic pollution also promotes the
distribution of coralline algae over the reef because they endure better
pollution compared with the thallomic macrophytes (Littler and Doty 1975).
The distribution of different taxa of Corallinaceae along the outer reef
slopes is controlled by illumination. Their species, which inhabit the deep
zone of the outer slope, are adapted to very low light. In transparent waters
they have been found down to depths of 350-400 m. They have a special red
pigment, phycoerythrin, which is assumed to further their light adaptation
(Littler 1972).
Reef bottom plant communities are subjected to the seasonal successional
changes (Benayahu and Loya 1977; Borowitzka et al. 1977). These changes
were especially well detectable at high-latitude reefs, such as those of Eilat
(Red Sea), where the winter association "Sargassum-Cystoseira-Colpomenia" in summer was replaced by the association" Stypopodium- TurbinariaLiagora" (Fig. 4.5). The succession was observed taking place also during
the formation of plant communities at the artificial reefs. Their surface
first was captured by the fast-growing filamentous or fleshy green algae
Calothrix, Cladophora, Sphacelaria, Microcoleus, Viva. They were then
grazed out by fish and replaced by firmer slow-growing algae, such as
Dictyota, Laurencia, Turbinaria, and by Corallinaceae (Tsuda and Kami
1973; Dollar 1982).
The phytocoene of bottom plant associations of coral reefs includes
abundant populations of epiphytic algae, living on thalloms of macrophytes
Benthic Microftora, Periphyton and Plant Associations
at the windward reef edges and over the algal ridges, being a main reef
builder in this zone of Indo-Pacific reefs. At the Atlantic reefs (Saint Croix,
Virgin Islands) the same turbulent zones are occupied by another crustose
coralline alga, Lithophyllum congestum (Adey 1975). This species is very
similar to P. oncoides in its spectrum of ecological adaptations. Growing on
reef edge, this alga constructs solid knolls, "boylers", exposed during the
ebbs, which in their structure are similar to the algal ridges of Indo-Pacific
atolls. On the algal ridges of numerous algal reefs in the Indian Ocean the
same function is accomplished had by Neogoniolithon frutescens.
Another mass species of Porolithon, P. gardineri, is also largely similar to
P. oncoides in its ecological characteristics, though it is less resistant to
wave-stress. Its colonies are not so monolithic as in P. oncoides, having
protuberances on their surface. The Sporolithon and the Hydrolithon are
adapted to a medium level of illumination and do not endure the strong
surf. They inhabit the shadowed calmer places under corals, under
macrophytes, or in trenches of flatts. These species also could be met with in
biotopes of outer reef slopees at depth of more than 10 m, where the surf
and the light conditions are optimal for them (Littler 1973b; Doty 1974; d.
Fig. 4.4). Coralline algae sustain better also the strong currents which often
happen to flow over the reef flat, and are less damaged by rubble which they
are moving up from the bottom. Therefore, they often replace the fleshy
macrophytes in parts of the flat subjected to strong wave-driven or tidal
currents (Doty 1974). The antropogenic pollution also promotes the
distribution of coralline algae over the reef because they endure better
pollution compared with the thallomic macrophytes (Littler and Doty 1975).
The distribution of different taxa of Corallinaceae along the outer reef
slopes is controlled by illumination. Their species, which inhabit the deep
zone of the outer slope, are adapted to very low light. In transparent waters
they have been found down to depths of 350-400 m. They have a special red
pigment, phycoerythrin, which is assumed to further their light adaptation
(Littler 1972).
Reef bottom plant communities are subjected to the seasonal successional
changes (Benayahu and Loya 1977; Borowitzka et al. 1977). These changes
were especially well detectable at high-latitude reefs, such as those of Eilat
(Red Sea), where the winter association "Sargassum-Cystoseira-Colpomenia" in summer was replaced by the association" Stypopodium- TurbinariaLiagora" (Fig. 4.5). The succession was observed taking place also during
the formation of plant communities at the artificial reefs. Their surface
first was captured by the fast-growing filamentous or fleshy green algae
Calothrix, Cladophora, Sphacelaria, Microcoleus, Viva. They were then
grazed out by fish and replaced by firmer slow-growing algae, such as
Dictyota, Laurencia, Turbinaria, and by Corallinaceae (Tsuda and Kami
1973; Dollar 1982).
The phytocoene of bottom plant associations of coral reefs includes
abundant populations of epiphytic algae, living on thalloms of macrophytes