Biological Factors of Formation and Erosion
21
it is within 40 to 60%. On most of the reefs Halimeda produces 10 to
50% of total carbonate material of soft sediments (coral sands). In the
Caribbean this genus is represented mainly by H. opunta, H. discoidea,
H. incrassata. In the GBR area of the Pacific the genera H. tuna, H. copiosa,
H. minima, and also the same H. opunta are most common (Drew and Abel
1983).
The red coralline algae (fam. Corallinaceae) are represented on reefs by
several common genera (d. Sect. 4.3.1). They form either weakly branching
articulose, knob-like or crustose solid lime colonies which well resist the
hydrodynamic stress. Coralline algae playa key role in processes of reef
growth and consolidation, especially at windward reef edges, where the
crustose or knob-like forms dominate, such as Porolithon, Sporolithon,
Lithophillum, Lithothamnium, Hydrolithon, and Neogoniolithon. Here they
find optimal conditions for their intensive growth: strong light and the
intensive surf which repells their grazers: parrot and sturgeon fish. They
deposit in their cell walls a mixture of calcite plus 25% of MgC03
(Borowitzka 1983). The rate of their linear growth at the margins of colonies
approximates 0.7 - 2 cm year, while their thickness growth ranges between
1-5mmyear- 1 (Adey and Vassar 1975). After the death of their cells the
crystallization of both these carbonates continues in them. This process
results in lithification of their colonies and thus in the building up of the flat
rocks (Littler 1972). The branching corallines Jania and Amphiroa, which
grow on the pieces of coral rubble, also finally cement them forming so the
solid rock. The main function of branching coralline algae is the production
of carbonaceous material of soft sediments, which was evaluated as being
within 20-40% of its total production by reef biota. This same share
belongs in coral sands to calcite, which is produced in reef environments
almost exclusively by corallines. The calcification in Corallinacea is lightdependent (Borowitzka 1979) but is less pronounced in them as compared
with corals: the ratio of Rc in the light and in the dark in these is -1.5 (d.
Table 1.2). Calcification in them is inhibited by DCMU, as in corals. It was
supposed that via photosynthesis some excess of ATP is produced in them,
which takes part in the energy supply of Ca 2 + -ions transport from seawater
to the zones of calcification in algal tissues (Barnes and Taylor 1973).
The results of Rc estimates in various reef calcifiers, animals and plants
are summarized in Table 1.3. In some branched coralline algae the rate of
calcification could be even higher than in corals, attaining 2 mg CaC03
g-lh- 1 . In crustose corallines, such as Porolithon, it is about the same as in
corals: 0.1-0.3mgCaC03 g- 1 h- 1 . A high rate of calcification have also the
thallomic calcareous algae Halimeda, Penicillus, Udotea - up to 2.9 mg
g-l h- 1 . Thus the thickets of these algae should produce 3-5 kg lime
m- 2 year- 1 . In corals realistic Rc values are equal to 0.2-0.6mgCaC03
g-l h- 1 . Their values given in Table 1.3, which Goreau (1963) obtained with
the use of 4sCa-label, were probably exaggerated due to taking no account
of possible isotopic exchange (Borowitzka 1979). The above rates of cal-
21
it is within 40 to 60%. On most of the reefs Halimeda produces 10 to
50% of total carbonate material of soft sediments (coral sands). In the
Caribbean this genus is represented mainly by H. opunta, H. discoidea,
H. incrassata. In the GBR area of the Pacific the genera H. tuna, H. copiosa,
H. minima, and also the same H. opunta are most common (Drew and Abel
1983).
The red coralline algae (fam. Corallinaceae) are represented on reefs by
several common genera (d. Sect. 4.3.1). They form either weakly branching
articulose, knob-like or crustose solid lime colonies which well resist the
hydrodynamic stress. Coralline algae playa key role in processes of reef
growth and consolidation, especially at windward reef edges, where the
crustose or knob-like forms dominate, such as Porolithon, Sporolithon,
Lithophillum, Lithothamnium, Hydrolithon, and Neogoniolithon. Here they
find optimal conditions for their intensive growth: strong light and the
intensive surf which repells their grazers: parrot and sturgeon fish. They
deposit in their cell walls a mixture of calcite plus 25% of MgC03
(Borowitzka 1983). The rate of their linear growth at the margins of colonies
approximates 0.7 - 2 cm year, while their thickness growth ranges between
1-5mmyear- 1 (Adey and Vassar 1975). After the death of their cells the
crystallization of both these carbonates continues in them. This process
results in lithification of their colonies and thus in the building up of the flat
rocks (Littler 1972). The branching corallines Jania and Amphiroa, which
grow on the pieces of coral rubble, also finally cement them forming so the
solid rock. The main function of branching coralline algae is the production
of carbonaceous material of soft sediments, which was evaluated as being
within 20-40% of its total production by reef biota. This same share
belongs in coral sands to calcite, which is produced in reef environments
almost exclusively by corallines. The calcification in Corallinacea is lightdependent (Borowitzka 1979) but is less pronounced in them as compared
with corals: the ratio of Rc in the light and in the dark in these is -1.5 (d.
Table 1.2). Calcification in them is inhibited by DCMU, as in corals. It was
supposed that via photosynthesis some excess of ATP is produced in them,
which takes part in the energy supply of Ca 2 + -ions transport from seawater
to the zones of calcification in algal tissues (Barnes and Taylor 1973).
The results of Rc estimates in various reef calcifiers, animals and plants
are summarized in Table 1.3. In some branched coralline algae the rate of
calcification could be even higher than in corals, attaining 2 mg CaC03
g-lh- 1 . In crustose corallines, such as Porolithon, it is about the same as in
corals: 0.1-0.3mgCaC03 g- 1 h- 1 . A high rate of calcification have also the
thallomic calcareous algae Halimeda, Penicillus, Udotea - up to 2.9 mg
g-l h- 1 . Thus the thickets of these algae should produce 3-5 kg lime
m- 2 year- 1 . In corals realistic Rc values are equal to 0.2-0.6mgCaC03
g-l h- 1 . Their values given in Table 1.3, which Goreau (1963) obtained with
the use of 4sCa-label, were probably exaggerated due to taking no account
of possible isotopic exchange (Borowitzka 1979). The above rates of cal-