158
Benthic Microflora, Periphyton and Plant Associations
4-8 generations per year by an average lifetime of only about 2 months for
individual thalloms (Vadas et al. 1980).
The form of light-dependence curves of photosynthesis in macrophytes
varied even within one species, depending of the level of ambient
illumination (Titlyanov et al. 1983b). Light saturation level of illumination
was usually attained in them at 5 to 10% of the incident surface PARS, e.g.,
at 8-30wt m- 2 with penetrated PARS of 250-350wt m- 2 . The level of light
saturation may also change several times depending even on the place where
sprouts for the experiments are obtained: from the top illuminated part of
the thallom or from its basal permanently shadowed part (Fig. 4.7). The
data prove the ability of the photosynthesic apparatus of macrophytes for
quick light adaptation to ambient conditions of illumination, which could
change during the individual life of an alga. This is one of the most
important ecophysiological features of reef macrophytes which provides
their high primary productivity. One of the ways of this adaptation is a
drastic increase in the chlorophyll content in thalloms, which could be 1.5-3
times more in their permanently shadowed parts compared with those well
illuminated (Titlyanov et al. 1983b, 1985). Another mechanism of light
adaptation is displayed in the changes of the vital form of thalloms. For
example, the green alga Caulerpa, when living on outer reef slopes at depths
of more than 10 m has filamentous thalloms, while the specimens living in
reef shallows have massive thalloms with short, thick branches (Jaubert
1981).
The available data on photosynthesis production and metabolic rates of
the benthic plant associations of various reefs are summarized in Table 4.18.
In bottom biotopes harboring macrophytes together with the coralline algae
the gross primary production values were at their average level: 35gCm- 2 day-l (Pauri 1988). Thus taking an average biomass of algae of
200 to 800 g C m -2 in this type of plant associations, the coefficients of
specific production PIB are close to 0.02-0.04day-l. In associations
dominated by the green calcareous algae Halimeda and Penicillum primary
production varie within 1 to 4 g C m -2 day-I. In bushes of macrophytes with
large massive fleshy thalloms, like Sargassum, Viva, Caulerpa, Cystoseira, as
well as in the dense turfs of filamentous or mini-thallomic algae (excluding
corallines), primary production happened to be very high, attaining the
upper limit to its rate known in natural plant communities: 1012gCm- 2 day-l with PIM ratios 2-4 and net photosynthesis rates of 47gCm- 2 day-l.
Photosynthesis production of reef benthic plant communities in biotopes
dominated by corals being 5-8gCm- 2 day-l, it is twice as much as in those
dominated by coralline algae. But in plant associations dominated by fleshy
macrophytes or by seagrasses it is commensurable to or even more than in
communities dominated by corals. The average content of chlorophyll a in
benthic plant communities varie within 100 to 250 J.lmg m -2 with plants
biomasses 1.5-4 kg m- 2 (wet weight). Thus 1 mg chlorophyll is contained in
Benthic Microflora, Periphyton and Plant Associations
4-8 generations per year by an average lifetime of only about 2 months for
individual thalloms (Vadas et al. 1980).
The form of light-dependence curves of photosynthesis in macrophytes
varied even within one species, depending of the level of ambient
illumination (Titlyanov et al. 1983b). Light saturation level of illumination
was usually attained in them at 5 to 10% of the incident surface PARS, e.g.,
at 8-30wt m- 2 with penetrated PARS of 250-350wt m- 2 . The level of light
saturation may also change several times depending even on the place where
sprouts for the experiments are obtained: from the top illuminated part of
the thallom or from its basal permanently shadowed part (Fig. 4.7). The
data prove the ability of the photosynthesic apparatus of macrophytes for
quick light adaptation to ambient conditions of illumination, which could
change during the individual life of an alga. This is one of the most
important ecophysiological features of reef macrophytes which provides
their high primary productivity. One of the ways of this adaptation is a
drastic increase in the chlorophyll content in thalloms, which could be 1.5-3
times more in their permanently shadowed parts compared with those well
illuminated (Titlyanov et al. 1983b, 1985). Another mechanism of light
adaptation is displayed in the changes of the vital form of thalloms. For
example, the green alga Caulerpa, when living on outer reef slopes at depths
of more than 10 m has filamentous thalloms, while the specimens living in
reef shallows have massive thalloms with short, thick branches (Jaubert
1981).
The available data on photosynthesis production and metabolic rates of
the benthic plant associations of various reefs are summarized in Table 4.18.
In bottom biotopes harboring macrophytes together with the coralline algae
the gross primary production values were at their average level: 35gCm- 2 day-l (Pauri 1988). Thus taking an average biomass of algae of
200 to 800 g C m -2 in this type of plant associations, the coefficients of
specific production PIB are close to 0.02-0.04day-l. In associations
dominated by the green calcareous algae Halimeda and Penicillum primary
production varie within 1 to 4 g C m -2 day-I. In bushes of macrophytes with
large massive fleshy thalloms, like Sargassum, Viva, Caulerpa, Cystoseira, as
well as in the dense turfs of filamentous or mini-thallomic algae (excluding
corallines), primary production happened to be very high, attaining the
upper limit to its rate known in natural plant communities: 1012gCm- 2 day-l with PIM ratios 2-4 and net photosynthesis rates of 47gCm- 2 day-l.
Photosynthesis production of reef benthic plant communities in biotopes
dominated by corals being 5-8gCm- 2 day-l, it is twice as much as in those
dominated by coralline algae. But in plant associations dominated by fleshy
macrophytes or by seagrasses it is commensurable to or even more than in
communities dominated by corals. The average content of chlorophyll a in
benthic plant communities varie within 100 to 250 J.lmg m -2 with plants
biomasses 1.5-4 kg m- 2 (wet weight). Thus 1 mg chlorophyll is contained in