Ecological and Physiological Aspects of Endosymbiosis
307
where they then settle (Kinzie et al. 1977; Fitt and Trench 1980). The stock
of zooxanthellae in reef waters is formed through the extrusion of their
excess by corals. Large amounts of zooxanthellae are released into the water
column from corals, and are damaged by corallovore reef animals like
parrot fish, urchins, etc. (Fitt and Trench 1980). The feces of corallovores
contain a lot of undigested living cysts of zooxanthellae, which then may
"infect" other hosts, the more so since the feces of fish are readily
swallowed by coral polyps (Parker 1984). Large quantities of zooxanthellaelike dinoflagellates were recorded to be present in waters of reef shallows
(Taylor 1980).
The composition of photosynthetic pigments in zooxanthellae is the same
as in the free-living planktonic dinoflagellates, like Peridinium or
Amphidium (Jeffrey and Haxo 1968; Titlyanov et al. 1980). They contain
chlorophylls a and c, plus a selection of additional carotenoid pigments
peridinine and dinoxanthines, specific for the dinoflagellates. The ratio of
chlorophylls c and a in zooxanthellae from different hosts is rather stable
(0.2-0.5). The content of chlorophyll in zooxanthellae varies between 512llg 10- 6 cells, between 15-50llg g-l of colony weight, or between 5251lg cm- 2 of its surface (d. Table 8.4). The total content of carotenoid
pigments is also high in them: ca. 2-51lg 10- 6 cells. In corals adapted to a
low illumination, the content of both groups of pigments in zooxanthellae
significantly increases (d. Table 8.6). Peridinine and other carotenoid
pigments are combined in the cells of zooxanthellae with chlorophylls, a
composition typical for the dinoflagellates' protein-pigment complexes
(PCP). They strongly enhance their efficiency in utilizing light energy in the
green range of 490 and 540 nm, thus increasing the ability of zooxanthellae
for photo adaptation (Zvalinski et al. 1978, 1980; Dustan 1979; Muscatine
1980). In fact, they have a lower threshold of light saturation compared with
diatoms (Scott and Jitts 1977), moreover, their large chloroplasts have a
specially structured labellar system, mentioned above.
The spectra of absorption of visible light in zooxanthellae have the main
maxima at 440 and 670 nm, and also additional but significant ones at
470-500 and 540 nm (Fig. 8.2). The latter are connected with the function of
PCP, mentioned above (Leletkin and Zvalinski 1981). The curves of action
spectra in their pigment system were estimated by measuring the rates of
14COr consumption at different wavelengths of light (Scott and Jitts 1977),
and those of the oxygen evolution (Halldall 1968; Zvalinski et al. 1980).
They differ from the curves of the absorption spectra, and this difference is
most significant just in the range of action of PSP - 470-600nm (Fig. 8.3). It
proves hour important their role is in light absorption by zooxanthellae in
deep reef habitats where blue-green light dominates. The absorption
maximum at 350-500 nm was especially well expressed in zooxanthellae of
symbiotic gorgonaceans, which are known to be enduring well light
deficiency (Fig. 8.4). The mechanism of light adaptation in zooxanthellae is
connected with their ability to enlarge the size of their photosynthesis units
307
where they then settle (Kinzie et al. 1977; Fitt and Trench 1980). The stock
of zooxanthellae in reef waters is formed through the extrusion of their
excess by corals. Large amounts of zooxanthellae are released into the water
column from corals, and are damaged by corallovore reef animals like
parrot fish, urchins, etc. (Fitt and Trench 1980). The feces of corallovores
contain a lot of undigested living cysts of zooxanthellae, which then may
"infect" other hosts, the more so since the feces of fish are readily
swallowed by coral polyps (Parker 1984). Large quantities of zooxanthellaelike dinoflagellates were recorded to be present in waters of reef shallows
(Taylor 1980).
The composition of photosynthetic pigments in zooxanthellae is the same
as in the free-living planktonic dinoflagellates, like Peridinium or
Amphidium (Jeffrey and Haxo 1968; Titlyanov et al. 1980). They contain
chlorophylls a and c, plus a selection of additional carotenoid pigments
peridinine and dinoxanthines, specific for the dinoflagellates. The ratio of
chlorophylls c and a in zooxanthellae from different hosts is rather stable
(0.2-0.5). The content of chlorophyll in zooxanthellae varies between 512llg 10- 6 cells, between 15-50llg g-l of colony weight, or between 5251lg cm- 2 of its surface (d. Table 8.4). The total content of carotenoid
pigments is also high in them: ca. 2-51lg 10- 6 cells. In corals adapted to a
low illumination, the content of both groups of pigments in zooxanthellae
significantly increases (d. Table 8.6). Peridinine and other carotenoid
pigments are combined in the cells of zooxanthellae with chlorophylls, a
composition typical for the dinoflagellates' protein-pigment complexes
(PCP). They strongly enhance their efficiency in utilizing light energy in the
green range of 490 and 540 nm, thus increasing the ability of zooxanthellae
for photo adaptation (Zvalinski et al. 1978, 1980; Dustan 1979; Muscatine
1980). In fact, they have a lower threshold of light saturation compared with
diatoms (Scott and Jitts 1977), moreover, their large chloroplasts have a
specially structured labellar system, mentioned above.
The spectra of absorption of visible light in zooxanthellae have the main
maxima at 440 and 670 nm, and also additional but significant ones at
470-500 and 540 nm (Fig. 8.2). The latter are connected with the function of
PCP, mentioned above (Leletkin and Zvalinski 1981). The curves of action
spectra in their pigment system were estimated by measuring the rates of
14COr consumption at different wavelengths of light (Scott and Jitts 1977),
and those of the oxygen evolution (Halldall 1968; Zvalinski et al. 1980).
They differ from the curves of the absorption spectra, and this difference is
most significant just in the range of action of PSP - 470-600nm (Fig. 8.3). It
proves hour important their role is in light absorption by zooxanthellae in
deep reef habitats where blue-green light dominates. The absorption
maximum at 350-500 nm was especially well expressed in zooxanthellae of
symbiotic gorgonaceans, which are known to be enduring well light
deficiency (Fig. 8.4). The mechanism of light adaptation in zooxanthellae is
connected with their ability to enlarge the size of their photosynthesis units