274
Communities of Corals in Reef Ecosystems
With the aid of submersibles the hermatypic corals Agaricia grahamae
and Montastrea cavernosa were found at depths down to 113 m where the
illumination was 0.15% PARS. The coral Eusmilia was found at 140m. On
the slopes of the Pacific atolls hermatypic corals were found ever deeper:
Pashyseris fastigata at a depth of 200 m, Coscinarea monilis at 270 m,
Psammocora explanulata, Scolymia lacera, Leptoseris porosa and L. fragilis
- at 140-165m (Lang 1974; Fricke and Schuhmaher 1983; Kuhlmann 1983;
Reed 1985; Fricke and Meischner 1985). These depths were far below the
depth of the compensation point of photosynthesis - respiration, which even
in corals best adapted to light deficiency in transparent oceanic waters was
located at depths of less than 100 m (Fricke and Schuhmacher 1983). Among
the ahermatypic corals at depths over 100 m, Madracis interjecta, M.
myriaster, Dendrophyllia miniscula, and Oculina varicosa were recorded.
These deep-water coral associations, which inhabit the lower zone of reef
slopes at depths over 80 m, do not form three-dimensional reef constructions
because of low calcification rates in the dark. On lots of bottom area
colonized by corals they compose kinds of patchy bioherms. The rate of
calcification there does not exceed the bioerosion of bioherm and coral
colonies. The calcareous sediments and rubble flow down the slope,
excluding so the possibility of formation of reefal construction (Fricke and
Hottinger 1983; Schuhmacher and Zibrovius 1985). Similar calcareous
bioherms are constructed on the continental slope down to depths of 1000 m
by the deep-water ahermatypic scleractinian corals Lophelia, Solenosmylia,
Madrepora (oculata) , Goniocorella, Desmophyllum, and Oculina (Keller
1976; Zibrovius 1980; Cairns and Stanley 1981).
Specific coral communities inhabit also lagoonal bottom biotopes covered
with soft sediments: carbonaceous silts, silted and pure coral sands. High
rates of sedimentation and the lack of solid substrate inhibit recruitment and
growth of normal sessile corals here. Nevertheless, the soft bottom biotopes
often appeared to be colonized by specific coral communities in which single
free-living corals dominate, such as Fungia, Diaseris, Cycloseris (fam.
Fungiidae), Heteropsammia (fam. Dendrophylliidae) and Heterocyathus
(fam. Caryophillidae). Ramose corals are also present in these communities,
e.g. Acropora, Pocillopora, Stylophora. Their planulae settle on the tridacna
shells or on large sections of the coral colonies. The corals Pocillopora,
Stylophora, Goniopora, Goniastrea, Euphillia, Pavona, Agaricella, and
Psammocora may live on soft bottom forming medium-sized round colonies
lying free on the surface. The main factors inhibiting coral growth in these
biotopes are siltation and the gradual submersion of their colonies into
the sediments. A number of corals escape this using various mechanisms.
Ramose corals, being rooted inside sediments with the aid of pieces of solid
substrates on which they settle, have a high growth rate, and thus may
overcome siltation. The round coral colonies, which lie free on the bottom,
are moved periodically by fish, which seek food under them, and so escape
the fate of being buried in the sediments (Glynn 1974). Fungiid free-living
Communities of Corals in Reef Ecosystems
With the aid of submersibles the hermatypic corals Agaricia grahamae
and Montastrea cavernosa were found at depths down to 113 m where the
illumination was 0.15% PARS. The coral Eusmilia was found at 140m. On
the slopes of the Pacific atolls hermatypic corals were found ever deeper:
Pashyseris fastigata at a depth of 200 m, Coscinarea monilis at 270 m,
Psammocora explanulata, Scolymia lacera, Leptoseris porosa and L. fragilis
- at 140-165m (Lang 1974; Fricke and Schuhmaher 1983; Kuhlmann 1983;
Reed 1985; Fricke and Meischner 1985). These depths were far below the
depth of the compensation point of photosynthesis - respiration, which even
in corals best adapted to light deficiency in transparent oceanic waters was
located at depths of less than 100 m (Fricke and Schuhmacher 1983). Among
the ahermatypic corals at depths over 100 m, Madracis interjecta, M.
myriaster, Dendrophyllia miniscula, and Oculina varicosa were recorded.
These deep-water coral associations, which inhabit the lower zone of reef
slopes at depths over 80 m, do not form three-dimensional reef constructions
because of low calcification rates in the dark. On lots of bottom area
colonized by corals they compose kinds of patchy bioherms. The rate of
calcification there does not exceed the bioerosion of bioherm and coral
colonies. The calcareous sediments and rubble flow down the slope,
excluding so the possibility of formation of reefal construction (Fricke and
Hottinger 1983; Schuhmacher and Zibrovius 1985). Similar calcareous
bioherms are constructed on the continental slope down to depths of 1000 m
by the deep-water ahermatypic scleractinian corals Lophelia, Solenosmylia,
Madrepora (oculata) , Goniocorella, Desmophyllum, and Oculina (Keller
1976; Zibrovius 1980; Cairns and Stanley 1981).
Specific coral communities inhabit also lagoonal bottom biotopes covered
with soft sediments: carbonaceous silts, silted and pure coral sands. High
rates of sedimentation and the lack of solid substrate inhibit recruitment and
growth of normal sessile corals here. Nevertheless, the soft bottom biotopes
often appeared to be colonized by specific coral communities in which single
free-living corals dominate, such as Fungia, Diaseris, Cycloseris (fam.
Fungiidae), Heteropsammia (fam. Dendrophylliidae) and Heterocyathus
(fam. Caryophillidae). Ramose corals are also present in these communities,
e.g. Acropora, Pocillopora, Stylophora. Their planulae settle on the tridacna
shells or on large sections of the coral colonies. The corals Pocillopora,
Stylophora, Goniopora, Goniastrea, Euphillia, Pavona, Agaricella, and
Psammocora may live on soft bottom forming medium-sized round colonies
lying free on the surface. The main factors inhibiting coral growth in these
biotopes are siltation and the gradual submersion of their colonies into
the sediments. A number of corals escape this using various mechanisms.
Ramose corals, being rooted inside sediments with the aid of pieces of solid
substrates on which they settle, have a high growth rate, and thus may
overcome siltation. The round coral colonies, which lie free on the bottom,
are moved periodically by fish, which seek food under them, and so escape
the fate of being buried in the sediments (Glynn 1974). Fungiid free-living