144
Benthic Microflora, Periphyton and Plant Associations
ecosystems. But this was soon changed (Doty 1974), as it was proved that
even on reefs with a rich coral growth such as the Enivetok atoll or the One
Tree reef, the primary production of bottom plant associations comprised
40-80% of the total primary production (Odum and Odum 1955;
Borowitzka et al. 1983). Their roles in primary production and in
calcification are moreover dominant in the so-called "algal" reefs, where
corals themselves are rare (Stoddart 1969; Womersly and Bailey 1969).
Peculiar features of reef plant associations are the high percentage of
calcareous red and green algae in them (e.g., of corallines and Halimeda), a
high taxonomic variability of their mini-thalloms or filamentous brown and
red algae, which often form kinds of periphytonic turfs, and a significant
abundance of epiphytic forms in them. These features of them are directly
connected with a high ratio between the actual areas occupied by reef plant
associations and the protective ones, which on reefs could be as high as 3 to
5 (Odum and Odum 1955; Dahl 1974). Additional areas are provided by the
dead ramose corals, by walls of caverns and trenches, rubble, the surface of
thalloms of large fleshy macrophytes, and by leaves of seagrasses. For
example, on a Caribbean reef the surface area of leaves of seagrass was
evaluated to be within 3.7-4.7m- z 1 m- z of bottom area, and about half of
the latter was occupied by epiphytic algae. The actual areas of solid
substrates per 1 m- z of bottom surface partly covered with rubble was
evaluated to be within 2-3m- z , in reef crest zones 1.4-1.6m- z , and in
thickets of ramose corals over 5. These excess surfaces are usually inhabited
by periphytonic turfs, mini-thalloms of brown and red algae, and coralline
algae. Inside numerous caverns and trenches poor light conditions limit
growth of other algae, exept the red ones. Thus they attain at the reef great
diversity and abundance.
The main factor controlling growth and composition of reef plant
associations is intensive grazing of them by herbivorous fish and
invertebrates (Earle 1972; Ogden 1976; Choat 1989). The grazing keep them
permanently in a juvenile stage of growth and development and induces in
them the domination of mini-thallomic fast-growing species, thus keeping
their specific production high. This makes for a high level of their primary
production in bottom reef biotopes, which, superficially viewed, does not
seem to be so abundant (Gribb 1973; Wanders 1976a). Plant associations of
coral reefs are a main source of organic detritus and dissolved organic
matter, as well as an important source of various biochemical metabolites,
like vitamins or antibiotics (Burkholder 1973). The plant detritus on many
reefs is produced also by mangroves (Colley et al. 1962).
4.3.1 Composition of Reef Plant Associations
The reef plant associations include five basic taxa of algae: diatoms, bluegreen algae, green, red and brown algae, and also the marine angiosperms -
Benthic Microflora, Periphyton and Plant Associations
ecosystems. But this was soon changed (Doty 1974), as it was proved that
even on reefs with a rich coral growth such as the Enivetok atoll or the One
Tree reef, the primary production of bottom plant associations comprised
40-80% of the total primary production (Odum and Odum 1955;
Borowitzka et al. 1983). Their roles in primary production and in
calcification are moreover dominant in the so-called "algal" reefs, where
corals themselves are rare (Stoddart 1969; Womersly and Bailey 1969).
Peculiar features of reef plant associations are the high percentage of
calcareous red and green algae in them (e.g., of corallines and Halimeda), a
high taxonomic variability of their mini-thalloms or filamentous brown and
red algae, which often form kinds of periphytonic turfs, and a significant
abundance of epiphytic forms in them. These features of them are directly
connected with a high ratio between the actual areas occupied by reef plant
associations and the protective ones, which on reefs could be as high as 3 to
5 (Odum and Odum 1955; Dahl 1974). Additional areas are provided by the
dead ramose corals, by walls of caverns and trenches, rubble, the surface of
thalloms of large fleshy macrophytes, and by leaves of seagrasses. For
example, on a Caribbean reef the surface area of leaves of seagrass was
evaluated to be within 3.7-4.7m- z 1 m- z of bottom area, and about half of
the latter was occupied by epiphytic algae. The actual areas of solid
substrates per 1 m- z of bottom surface partly covered with rubble was
evaluated to be within 2-3m- z , in reef crest zones 1.4-1.6m- z , and in
thickets of ramose corals over 5. These excess surfaces are usually inhabited
by periphytonic turfs, mini-thalloms of brown and red algae, and coralline
algae. Inside numerous caverns and trenches poor light conditions limit
growth of other algae, exept the red ones. Thus they attain at the reef great
diversity and abundance.
The main factor controlling growth and composition of reef plant
associations is intensive grazing of them by herbivorous fish and
invertebrates (Earle 1972; Ogden 1976; Choat 1989). The grazing keep them
permanently in a juvenile stage of growth and development and induces in
them the domination of mini-thallomic fast-growing species, thus keeping
their specific production high. This makes for a high level of their primary
production in bottom reef biotopes, which, superficially viewed, does not
seem to be so abundant (Gribb 1973; Wanders 1976a). Plant associations of
coral reefs are a main source of organic detritus and dissolved organic
matter, as well as an important source of various biochemical metabolites,
like vitamins or antibiotics (Burkholder 1973). The plant detritus on many
reefs is produced also by mangroves (Colley et al. 1962).
4.3.1 Composition of Reef Plant Associations
The reef plant associations include five basic taxa of algae: diatoms, bluegreen algae, green, red and brown algae, and also the marine angiosperms -