Nutrients
Fig. 2.8. Consumption of ammonia from
water by coral Pocillopora in the light (1) and
in the dark (2), as well as its release by
ahermatypic coral Tubastrea in the light (3); N
NH4 content in water; T exposure time. (After
Muscatine and D'Elia 1978)
1
51
2
T, /to{frs
excrete Nand P but cannot consume them (Muscatine et al. 1979; Muscatine
1980; ct. Fig. 2.8). The saturation curves of consumption of P04, N03 and
NH4 by corals are similar to the Michaelis-Menten kinetic curve (D'Elia
1978; Webb and Wiebe 1978; Muscatine and D'Elia 1978). This indicates
that the consumption proceeds mainly via the enzymatic active transport
mechanisms. The threshold concentrations at which the consumption starts
are within 0.1-0.2Ilmoll-r, and that of Vrnax 1-2Ilmoll-l, which is the
same range as in the oceanic phytoplankton. The rate of consumption of
ammonia by corals was twice as much as that of nitrates in their ambient
concentrations (D'Elia and Webb 1977). The ions of N0 3 , being consumed
by the epithelial cells of polyps, are then transferred into the cells of
zooxanthellae, where they are reduced to ammonium and involved in the
biosynthesis via glutamine as an intermediary. A large portion of the amino
acids thus produced is then translocated back to the polyp's cell (Muscatine
1980; Crossland and Barnes 1977a). The incubation of coral with N 15 0 3
resulted in the accumulation of N 15 in its tissues in organic form (Marian
1979).
The inorganic phosphate consumed by corals is accumulated in the cells
of zooxanthellae, where it is incorporated into ATP and nucleotides, which
are then largely translocated into the hosts's cells. In them this phosphorus
is mineralized to P04-P, which is again consumed by zooxanthellae, thus
closing the cycle. The above mechanism provides the semi-closed cycle of
nutrients in symbiotic animals, which drastically decreases their loss by such
animals to the surrounding waters. Nevertheless, even the symbiotic animals
(corals) excrete some amounts of P04-P and NH4-N. Therefore, the abovementioned estimations of their uptake by corals by measurements of the
decrease in their content present in water are conventional. The values thus
received have reflected not a real uptake, but an indefinite equilibrium value
Fig. 2.8. Consumption of ammonia from
water by coral Pocillopora in the light (1) and
in the dark (2), as well as its release by
ahermatypic coral Tubastrea in the light (3); N
NH4 content in water; T exposure time. (After
Muscatine and D'Elia 1978)
1
51
2
T, /to{frs
excrete Nand P but cannot consume them (Muscatine et al. 1979; Muscatine
1980; ct. Fig. 2.8). The saturation curves of consumption of P04, N03 and
NH4 by corals are similar to the Michaelis-Menten kinetic curve (D'Elia
1978; Webb and Wiebe 1978; Muscatine and D'Elia 1978). This indicates
that the consumption proceeds mainly via the enzymatic active transport
mechanisms. The threshold concentrations at which the consumption starts
are within 0.1-0.2Ilmoll-r, and that of Vrnax 1-2Ilmoll-l, which is the
same range as in the oceanic phytoplankton. The rate of consumption of
ammonia by corals was twice as much as that of nitrates in their ambient
concentrations (D'Elia and Webb 1977). The ions of N0 3 , being consumed
by the epithelial cells of polyps, are then transferred into the cells of
zooxanthellae, where they are reduced to ammonium and involved in the
biosynthesis via glutamine as an intermediary. A large portion of the amino
acids thus produced is then translocated back to the polyp's cell (Muscatine
1980; Crossland and Barnes 1977a). The incubation of coral with N 15 0 3
resulted in the accumulation of N 15 in its tissues in organic form (Marian
1979).
The inorganic phosphate consumed by corals is accumulated in the cells
of zooxanthellae, where it is incorporated into ATP and nucleotides, which
are then largely translocated into the hosts's cells. In them this phosphorus
is mineralized to P04-P, which is again consumed by zooxanthellae, thus
closing the cycle. The above mechanism provides the semi-closed cycle of
nutrients in symbiotic animals, which drastically decreases their loss by such
animals to the surrounding waters. Nevertheless, even the symbiotic animals
(corals) excrete some amounts of P04-P and NH4-N. Therefore, the abovementioned estimations of their uptake by corals by measurements of the
decrease in their content present in water are conventional. The values thus
received have reflected not a real uptake, but an indefinite equilibrium value