370
Biogeochemical Metabolism and Energy Flows in Reef Ecosystems
showed that they could be heterotrophic as well: Pt/Mt < 1 (Gordon and
Kelley 1962; Goreau et al. 1971; Kinsey 1985b). But on an average, in most
reef systems the autotrophic and heterotrophic processes are well balanced
within the whole reef (Pt/Mt ~ 1), notwithstanding the fact that within a
separate one of their biotopes (lagoons) it could be <1, or (reef fiat, reef
slope) >1 (Kinsey 1983; Sorokin 1986b; Zharikov 1987). In a well-balanced
system, where the gross photosynthesis is in balance with the total
heterotrophic respiration, the net autotrophic production (P n = Pt - Mt )
should be around zero. But the exploitation of reef resources by man
without ruining the ecosystem could proceed only at the expense of the net
autotrophic production (more correctly, the net external energy input).
Therefore, the estimation of the exact size of the total net production P n in
reef ecosystems becomes extremely important from the viewpoint of their
monitoring and preservation (Kinsey 1985b).
But the problem of correct evaluation of P n does not appear to be as
simple as it seems to be. As in any open system in coral-reef ecosystems the
gross autotrophic production (Pt) is not actually equivalent to the total input
of energy (P g), nor is its total energy expenditure (Mg) equivalent to the
respiratory losses measured (Mt). The P g' besides Pt, includes also the
energy of the external organic matter entering the reef system from the land
with drainage and river waters, from mangrove thickets, from the ocean as
drifting blue-green algae, or as oceanic plankton consumed by reef filterers
and planktonovores (cf. Sects. 3.1.2, 6.3.2). As regards the values of Mg,
besides respiration losses reef ecosystems lose a significant protion of energy
as organic metter into the surrounding ocean and into bottom sediments.
The level of gross autotrophic production in most kinds of reef bottom
biotopes is usually very high and will often reach top level, as known in the
most productive communities of our planet, like the tropical rain forests, in
the thickets of macrophytes at the temperate-zone shelf in summer, or the
areas of intensive upwelling in the oceans: 8-15 g C m- 2 day- I. This level of
Pt becomes possible because of the multilayer or tree-dimentional structure
of photosynthetic elements of the community within the illuminated zone
and because the level of light saturation in them is less than the maximum
day time illumination (Odum et al. 1958; Dahl 1976; Jokiel and Morrissey
1986; Table 10.1, Fig. 10.2). The basic producing agents of the reef: corals,
macrophytes, seagrasses, compose the ramose multilayer structures whose
functional surface of illuminated areas several times exceed the proajective
area of the bottom. Among the main elements contributing to reef primary
production are the zooxanthellae of symbiotic animals (corals, zoantharians,
forams, clams), the benthic algae (macrophytes, filamentous algae of turfs
and periphyton, micro algae of microphytobenthos, coralline and endolythic
algae), the seagrasses (Lewis 1977b) and, occasionally, the phytoplankton
(cf. Sects. 4.2,4.3).
The methodology problems in measurements of reef biogeochemical
metabolism and the main results were reviewed by Lewis (1977b, 1981),
Biogeochemical Metabolism and Energy Flows in Reef Ecosystems
showed that they could be heterotrophic as well: Pt/Mt < 1 (Gordon and
Kelley 1962; Goreau et al. 1971; Kinsey 1985b). But on an average, in most
reef systems the autotrophic and heterotrophic processes are well balanced
within the whole reef (Pt/Mt ~ 1), notwithstanding the fact that within a
separate one of their biotopes (lagoons) it could be <1, or (reef fiat, reef
slope) >1 (Kinsey 1983; Sorokin 1986b; Zharikov 1987). In a well-balanced
system, where the gross photosynthesis is in balance with the total
heterotrophic respiration, the net autotrophic production (P n = Pt - Mt )
should be around zero. But the exploitation of reef resources by man
without ruining the ecosystem could proceed only at the expense of the net
autotrophic production (more correctly, the net external energy input).
Therefore, the estimation of the exact size of the total net production P n in
reef ecosystems becomes extremely important from the viewpoint of their
monitoring and preservation (Kinsey 1985b).
But the problem of correct evaluation of P n does not appear to be as
simple as it seems to be. As in any open system in coral-reef ecosystems the
gross autotrophic production (Pt) is not actually equivalent to the total input
of energy (P g), nor is its total energy expenditure (Mg) equivalent to the
respiratory losses measured (Mt). The P g' besides Pt, includes also the
energy of the external organic matter entering the reef system from the land
with drainage and river waters, from mangrove thickets, from the ocean as
drifting blue-green algae, or as oceanic plankton consumed by reef filterers
and planktonovores (cf. Sects. 3.1.2, 6.3.2). As regards the values of Mg,
besides respiration losses reef ecosystems lose a significant protion of energy
as organic metter into the surrounding ocean and into bottom sediments.
The level of gross autotrophic production in most kinds of reef bottom
biotopes is usually very high and will often reach top level, as known in the
most productive communities of our planet, like the tropical rain forests, in
the thickets of macrophytes at the temperate-zone shelf in summer, or the
areas of intensive upwelling in the oceans: 8-15 g C m- 2 day- I. This level of
Pt becomes possible because of the multilayer or tree-dimentional structure
of photosynthetic elements of the community within the illuminated zone
and because the level of light saturation in them is less than the maximum
day time illumination (Odum et al. 1958; Dahl 1976; Jokiel and Morrissey
1986; Table 10.1, Fig. 10.2). The basic producing agents of the reef: corals,
macrophytes, seagrasses, compose the ramose multilayer structures whose
functional surface of illuminated areas several times exceed the proajective
area of the bottom. Among the main elements contributing to reef primary
production are the zooxanthellae of symbiotic animals (corals, zoantharians,
forams, clams), the benthic algae (macrophytes, filamentous algae of turfs
and periphyton, micro algae of microphytobenthos, coralline and endolythic
algae), the seagrasses (Lewis 1977b) and, occasionally, the phytoplankton
(cf. Sects. 4.2,4.3).
The methodology problems in measurements of reef biogeochemical
metabolism and the main results were reviewed by Lewis (1977b, 1981),