Bottom Plant Associations
155
and on leaves of seagrasses. They are represented by all the main taxa of
marine algae. Most common epiphytes among blue-greens are Oscillatoria,
Calotrix, Dichotrix, and Plectonema. The thallomic epiphytes have mostly
tiny filamentous thalloms l-l.S cm long. Among them the most numerous
are the green algae Cladophora, Enteromorpha, Ch lorodesm us , Ulvella,
Derbesia, the brown algae Ectocarpus, Sphacelaria, Myrionema, Giffordia,
and the red algae Ceramium, Polysiphonia, Hypnea, Chondria, Gelidiel/a,
Griffithsia, Jania, and Amphiroa. The red algae are usually dominating also
in the epiphytic plant communities (Fortes 1981; Norris and Bucher 1982).
These communities have a high degree of species variability. For example
on thalloms of only two species of Sargassum there were found over 70
species of epiphytic algae.
The reef seagrasses prefer shallow plain bottom areas of lagoons, covered
with fine coral sands or with silty sands, with a depth of water during the
ebb of 0.2-1 m. They form in such biotopes dense meadows or so called
"seagrass beds" (Zieman 1975; Tsuda 1979). The thickets of seagrass beds
are usually formed by one or two species of seagrass with of one of them
dominating in the last case (Zieman et al. 1979). On the bottom of deeper
parts of lagoons and on stripes of sandy bottom of reef flats they usually
form mixed communities together with the macrophytes. Amid the abovementioned seagrass beds are situated patches of bare sandy bottom - socalled "halos". The halos are situated usually around large corals, patch
reefs or near the edges of lagoonal reefs. They are formed as a result of
grazing activities of herbivorous fish and urchins, which have refuges in the
above-mentioned corals or in patch reefs. In daytime the grazers are hidden
in their refuges, and at night they go to their pasture areas, plucking off first
the plants near their hiding places (Ogden et al. 1973; Anzari et al. 1991).
4.3.3 Biomass, Metabolism, Features of Ecology
The projective cover of the reef bottom surface by plant communities varies
in its different zones from 10 to 100%. The largest coverage could be
observed usually in areas of lagoons and reef flats, and the smaller at outer
reef slopes (Tables 4.1S, 4.16). On an average, the projective cover of
bottom by plant associations varies within 20-30% in the lagoons, 40-80%
on reef flats, and S-20% on outer reef slopes. Their biomass varies
correspondingly within the same scale (Table 4.17). On the reef flat, while
20-40% of its surface is covered by coralline algae, their wet biomass varies
within 1-Skgm- 2 . But at flats covered more than SO% by the fleshy
macrophytes, the plant biomass is more: 3 to 8kgm- 2 . On the bottom of
lagoons and on submerged parts of reef flats covered with thickets of
seagrasses or Halimeda the biomass could attain 1S-22kgm- 1 . In thickets
of Sargassum biomass is usually 1-4kgm-2. On seagrass beds it is on an
average within 2 to 8kgm- 2 (Tables 4.14,4.17).
155
and on leaves of seagrasses. They are represented by all the main taxa of
marine algae. Most common epiphytes among blue-greens are Oscillatoria,
Calotrix, Dichotrix, and Plectonema. The thallomic epiphytes have mostly
tiny filamentous thalloms l-l.S cm long. Among them the most numerous
are the green algae Cladophora, Enteromorpha, Ch lorodesm us , Ulvella,
Derbesia, the brown algae Ectocarpus, Sphacelaria, Myrionema, Giffordia,
and the red algae Ceramium, Polysiphonia, Hypnea, Chondria, Gelidiel/a,
Griffithsia, Jania, and Amphiroa. The red algae are usually dominating also
in the epiphytic plant communities (Fortes 1981; Norris and Bucher 1982).
These communities have a high degree of species variability. For example
on thalloms of only two species of Sargassum there were found over 70
species of epiphytic algae.
The reef seagrasses prefer shallow plain bottom areas of lagoons, covered
with fine coral sands or with silty sands, with a depth of water during the
ebb of 0.2-1 m. They form in such biotopes dense meadows or so called
"seagrass beds" (Zieman 1975; Tsuda 1979). The thickets of seagrass beds
are usually formed by one or two species of seagrass with of one of them
dominating in the last case (Zieman et al. 1979). On the bottom of deeper
parts of lagoons and on stripes of sandy bottom of reef flats they usually
form mixed communities together with the macrophytes. Amid the abovementioned seagrass beds are situated patches of bare sandy bottom - socalled "halos". The halos are situated usually around large corals, patch
reefs or near the edges of lagoonal reefs. They are formed as a result of
grazing activities of herbivorous fish and urchins, which have refuges in the
above-mentioned corals or in patch reefs. In daytime the grazers are hidden
in their refuges, and at night they go to their pasture areas, plucking off first
the plants near their hiding places (Ogden et al. 1973; Anzari et al. 1991).
4.3.3 Biomass, Metabolism, Features of Ecology
The projective cover of the reef bottom surface by plant communities varies
in its different zones from 10 to 100%. The largest coverage could be
observed usually in areas of lagoons and reef flats, and the smaller at outer
reef slopes (Tables 4.1S, 4.16). On an average, the projective cover of
bottom by plant associations varies within 20-30% in the lagoons, 40-80%
on reef flats, and S-20% on outer reef slopes. Their biomass varies
correspondingly within the same scale (Table 4.17). On the reef flat, while
20-40% of its surface is covered by coralline algae, their wet biomass varies
within 1-Skgm- 2 . But at flats covered more than SO% by the fleshy
macrophytes, the plant biomass is more: 3 to 8kgm- 2 . On the bottom of
lagoons and on submerged parts of reef flats covered with thickets of
seagrasses or Halimeda the biomass could attain 1S-22kgm- 1 . In thickets
of Sargassum biomass is usually 1-4kgm-2. On seagrass beds it is on an
average within 2 to 8kgm- 2 (Tables 4.14,4.17).