282
Communities of Corals in Reef Ecosystems
damage corals not less severely than the direct physical impact of waves
(Johannes 1975). The same inhibition and even the death of corals could be
caused by a lack of light at lagoonal bottoms accompanying an increase in
turbidity during continuous storms (Dodge et al. 1974; Rogers 1979b).
Increased stress of siltation has a direct impact on the physiologial state of
corals. Their respiration increases through the decreasing photosynthesis
rate and the Pt/Mt-ratio (Abdel Salam and Porter 1988). The siltation and
the weak light inhibit also the recruitment of corals planulae (Johannes
1972a). The siltation stress stimulated the evolutional appearance of corals
with an increased ability to endure siltation, and actively sift out settling
suspended material (Yonge 1940; Lewis and Price 1976). These corals may
survive in very turbid waters (Roy and Smith 1971; Loya 1976c). Among
these are the Atlantic corals Siderastrea siderea (Kiihlmann 1974),
Montastrea cavernosa and Diploria strigosa (Lasker 1980). It is just these
corals that are usually pioneering in the colonization of turbid shallow
biotopes (Hubbard 1974). A high rate of sifting out sediments is peculiar to
fungiids, which successfully colonize biotopes of turbulent reef zones with
turbid waters.
Corals get rid of sediments by making them sticky with mucus and
expelling them with the aid of cilia and tentacles (Hubbard and Pocock
1972). Their ability to expel sediments depends also upon the geometry of
corallites (Hubbard 1973). Corals which actively expel sediments have many
well-developed septa and relatively large and tall corallites. Among such
corals are the above-mentioned Montastrea, Diploria, and also many of
other faviids: Meandrina, Symphillia, Lobophyllia, Fungia, and Galaxea.
These corals are good survivors, also living in turbid waters in biotopes with
very rapid sedimentation (Roy and Smith 1971; Loya 1975; Schuhmacher
1979). In contrast, such corals as Agaricia, which have rare and
underdeveloped septa cannot quickly expel sediment so that they can live
only in clean, deep waters at steep, deep zones of reef slopes.
Light as a physical factor influences the structure of coral communities
only in the upper shallow and in the deep zones of the reef. In the upper
zone corals might be inhibited by an excess of light (Siebeck 1981). But the
coenosarc of corals contains protective pigments and amino acid
mycosporine which absorb ultraviolet Radiation (Chalker et al. 1988). The
deficiency of light begins to influence species composition of coral
communities only in biotopes, where illumination drops down to 3-5% of
PARS, that is in caves and in other shadowed places of reef flats and of the
upper part of reef slopes, and also in the deep zone of the fore-reef and reef
base. In coral communities here many ahermatypic species and the
specialized hermatypic corals appear, which are adapted to a low
illumination. They may live without signs of bleaching at an illumination as
low as 1 % PARS. These are Leptoseris, Cycloseris, and Pashyseris. At an
illumination of 2-3% PARS communities of corals include species of
scyophilic hermatypic scleractinians like Leptastrea, Scolymia, Turbinaria,
Communities of Corals in Reef Ecosystems
damage corals not less severely than the direct physical impact of waves
(Johannes 1975). The same inhibition and even the death of corals could be
caused by a lack of light at lagoonal bottoms accompanying an increase in
turbidity during continuous storms (Dodge et al. 1974; Rogers 1979b).
Increased stress of siltation has a direct impact on the physiologial state of
corals. Their respiration increases through the decreasing photosynthesis
rate and the Pt/Mt-ratio (Abdel Salam and Porter 1988). The siltation and
the weak light inhibit also the recruitment of corals planulae (Johannes
1972a). The siltation stress stimulated the evolutional appearance of corals
with an increased ability to endure siltation, and actively sift out settling
suspended material (Yonge 1940; Lewis and Price 1976). These corals may
survive in very turbid waters (Roy and Smith 1971; Loya 1976c). Among
these are the Atlantic corals Siderastrea siderea (Kiihlmann 1974),
Montastrea cavernosa and Diploria strigosa (Lasker 1980). It is just these
corals that are usually pioneering in the colonization of turbid shallow
biotopes (Hubbard 1974). A high rate of sifting out sediments is peculiar to
fungiids, which successfully colonize biotopes of turbulent reef zones with
turbid waters.
Corals get rid of sediments by making them sticky with mucus and
expelling them with the aid of cilia and tentacles (Hubbard and Pocock
1972). Their ability to expel sediments depends also upon the geometry of
corallites (Hubbard 1973). Corals which actively expel sediments have many
well-developed septa and relatively large and tall corallites. Among such
corals are the above-mentioned Montastrea, Diploria, and also many of
other faviids: Meandrina, Symphillia, Lobophyllia, Fungia, and Galaxea.
These corals are good survivors, also living in turbid waters in biotopes with
very rapid sedimentation (Roy and Smith 1971; Loya 1975; Schuhmacher
1979). In contrast, such corals as Agaricia, which have rare and
underdeveloped septa cannot quickly expel sediment so that they can live
only in clean, deep waters at steep, deep zones of reef slopes.
Light as a physical factor influences the structure of coral communities
only in the upper shallow and in the deep zones of the reef. In the upper
zone corals might be inhibited by an excess of light (Siebeck 1981). But the
coenosarc of corals contains protective pigments and amino acid
mycosporine which absorb ultraviolet Radiation (Chalker et al. 1988). The
deficiency of light begins to influence species composition of coral
communities only in biotopes, where illumination drops down to 3-5% of
PARS, that is in caves and in other shadowed places of reef flats and of the
upper part of reef slopes, and also in the deep zone of the fore-reef and reef
base. In coral communities here many ahermatypic species and the
specialized hermatypic corals appear, which are adapted to a low
illumination. They may live without signs of bleaching at an illumination as
low as 1 % PARS. These are Leptoseris, Cycloseris, and Pashyseris. At an
illumination of 2-3% PARS communities of corals include species of
scyophilic hermatypic scleractinians like Leptastrea, Scolymia, Turbinaria,