20
Reef Lime Constructions
be coincide with the corresponding light curves of photosynthesis (Barnes
and Taylor 1973). The dependence of Rc upon the ambient light intensity
(J) derived from these curves looks as follows: Rc = Rcm . tgJ/Jk, where:
Rcm is the maximal rate of calcification, J the observed and Jk the optimal
illumination (Chalker 1983). Thus the values of Rc, and correspondingly the
coral's growth rates, should decrease with depth due to the decrease of light.
But, actually, because of light adaptation of the photosynthetic apparatus of
their zooxanthellae (cf. Sect. 8.3), it does not significantly decrease down to
a depth 20 m in transparent waters (Buddemeyer et al. 1974; Dustan 1975;
Barnes and Taylor 1973). However in deeper waters the Rc and the coral
growth rate usually slow down (Gareau 1963; Huston 1985).
Second in importance among animal symbiotic calcifiers in reef
ecosystems are the foraminifera. Some of their species, which live in coral
sands, are real giants in the protozoan's world, having a diameter of 5-8 mm
("sand dollars"). They grow up to a volume of 0.2-0.3 cm 3 during 2-3 years
(Ross 1977), while the small also symbiotic benthic forams, living in shallow
temperate environments, but having for symbionts cyanobacteria instead of
Zooxanthellae, attain their maximal size only after 5-6 years. The rate of
calcification in hermatypic forams is dependent upon light, as in corals
(Duguay and Taylor 1978). Forams produce around 15% of the total lime
material of coral sands (Maxwell 1968; cf. Sect. 5.5.8). Remarkable calcifiers
on reefs are also the large hermatypic bivalves tridacnids (cf. Sect. 5.1.3).
Their shells are an important element in lime rock of the Pleistocene as well
as of modern reefs (Chapell and Polach 1976). A definite role in the
production of lime on reefs is played also by numerous ahermatypic animals,
which have carbonate elements in their skeletons such as carapaces, needles,
spicules, radules, shells, globules. Among them there are urchins, asteroids,
crinoids, holothurians, various molluscs, crabs, sedentary polychaetes,
bryozoans, sponges, soft corals (Chave et al. 1972; Maxwell 1973; CUffey
1977).
The function of calcification is peculiar also to numerous representatives
of seaweeds inhabiting reefs. In total, they comprise about 100 genera of
calcareous algae (Borowitzka 1977). Most of the thallomic calcareous
macrophytes deposit CaC03 in the form of aragonite orthorhomboid crystals
in their cell walls or in the intercellular spaces. Among these are the red
algae from the family. Peyssonelliaceae, the green algae Dascillus, Caulerpa
and the brown alga Pagina. The coralline algae deposit in their cell walls
crystals of calcite. The blue-green algae from the family. Nostocales
accumulate in their mucus small globules of calcite. In some algae calcium
accumulates inside the cells in the form of Ca-oxalate (Acetabularia).
The most powerful calcifier among the reef macrophytes are the
Halimeda and the red Corallinacea (Goreau 1963; Littler and Doty 1975;
Borowitzka 1983). The contents of CaC03 in Halimeda is as high as 9090% of dry weight of its thalloms, while in other green calcareous algae
from the same family Udoteaceae, like Udotea, Penicillus, Riphoclavus
Reef Lime Constructions
be coincide with the corresponding light curves of photosynthesis (Barnes
and Taylor 1973). The dependence of Rc upon the ambient light intensity
(J) derived from these curves looks as follows: Rc = Rcm . tgJ/Jk, where:
Rcm is the maximal rate of calcification, J the observed and Jk the optimal
illumination (Chalker 1983). Thus the values of Rc, and correspondingly the
coral's growth rates, should decrease with depth due to the decrease of light.
But, actually, because of light adaptation of the photosynthetic apparatus of
their zooxanthellae (cf. Sect. 8.3), it does not significantly decrease down to
a depth 20 m in transparent waters (Buddemeyer et al. 1974; Dustan 1975;
Barnes and Taylor 1973). However in deeper waters the Rc and the coral
growth rate usually slow down (Gareau 1963; Huston 1985).
Second in importance among animal symbiotic calcifiers in reef
ecosystems are the foraminifera. Some of their species, which live in coral
sands, are real giants in the protozoan's world, having a diameter of 5-8 mm
("sand dollars"). They grow up to a volume of 0.2-0.3 cm 3 during 2-3 years
(Ross 1977), while the small also symbiotic benthic forams, living in shallow
temperate environments, but having for symbionts cyanobacteria instead of
Zooxanthellae, attain their maximal size only after 5-6 years. The rate of
calcification in hermatypic forams is dependent upon light, as in corals
(Duguay and Taylor 1978). Forams produce around 15% of the total lime
material of coral sands (Maxwell 1968; cf. Sect. 5.5.8). Remarkable calcifiers
on reefs are also the large hermatypic bivalves tridacnids (cf. Sect. 5.1.3).
Their shells are an important element in lime rock of the Pleistocene as well
as of modern reefs (Chapell and Polach 1976). A definite role in the
production of lime on reefs is played also by numerous ahermatypic animals,
which have carbonate elements in their skeletons such as carapaces, needles,
spicules, radules, shells, globules. Among them there are urchins, asteroids,
crinoids, holothurians, various molluscs, crabs, sedentary polychaetes,
bryozoans, sponges, soft corals (Chave et al. 1972; Maxwell 1973; CUffey
1977).
The function of calcification is peculiar also to numerous representatives
of seaweeds inhabiting reefs. In total, they comprise about 100 genera of
calcareous algae (Borowitzka 1977). Most of the thallomic calcareous
macrophytes deposit CaC03 in the form of aragonite orthorhomboid crystals
in their cell walls or in the intercellular spaces. Among these are the red
algae from the family. Peyssonelliaceae, the green algae Dascillus, Caulerpa
and the brown alga Pagina. The coralline algae deposit in their cell walls
crystals of calcite. The blue-green algae from the family. Nostocales
accumulate in their mucus small globules of calcite. In some algae calcium
accumulates inside the cells in the form of Ca-oxalate (Acetabularia).
The most powerful calcifier among the reef macrophytes are the
Halimeda and the red Corallinacea (Goreau 1963; Littler and Doty 1975;
Borowitzka 1983). The contents of CaC03 in Halimeda is as high as 9090% of dry weight of its thalloms, while in other green calcareous algae
from the same family Udoteaceae, like Udotea, Penicillus, Riphoclavus