Nutrients
59
compounds of bottom biotopes have in their microstructures the autotrophic
micro- and macro algae , which consume P04-P, and the heterotrophies,
which release it (cf. Sect. 4.1). These compounds function within these
structures in a narrow coincidence, providing a semi-closed cycling of
nutrients, the same as between zooxanthellae and polyp tissues in coral.
Moreover, not only the absolute rates of Ac and Ae flows of P04-P, but
even their· ratios and the 24-h balances of P04-P coincided well in
periphyton and in the living corals, being calculated per 1 g of dry weight of
hard substrate (Table 2.5). The best coincidence was found in experiments
with the living and the dead parts of the same ramose colony, if the latter is
overgrown with the periphyton. This coincidence looks more logical if we
take into the account that the rates of photosynthesis and respiration in
living corals and in dead corals overgrown with periphyton also coincide (cf.
Sect. 4.2).
An analysis of the table shows that the flow rates of P04-P between
periphyton and water and the ratios between its consumption and release
depend upon its concentration in water. The same was shown by Atkinson
(1987). At low P04-P content, similar to the ambient ones in waters over
reefs of the Heron I. (0.1-0.3 Jlmoll- 1 ), the rate of consumption of P04-P
(Ap) by the periphyton over the piece of flat rocks and over the coral rubble
was within 1O-60JlgPkg- 1 of dry matter h- 1 . That is commensurable with
the same values in living corals (Tables 2.3, 2.5), as measured at the same
low ambient concentrations. At these low concentrations of P04-P in water
the rate of the reciprocal excretion flow (Ac) was equal to the rates of the
consumption (At) and sometimes it was even higher. In these cases, which
are usual at a low P04-P content, the net release of P04-P proceeded, and
thus the balance value At was positive (Table 2.5, Fig. 2.11). In the enriched
water, where the P04-P was 0.5-3.5Jlmol, the consumption flow in
periphytic microcosms increased up to 80-120 Jlg P kg- I h -I, while the
excretion flow was not so dependent upon the external P04-P content and
increased much less. Thus, in the enriched water consumption was 1.5-3
times more than excretion, and the net uptake of P04-P readily took place.
Thus at high P04-P concentrations the balance values At were always
negative - the periphytonic communities did not release any P04-P into the
water, but only consumed it. One could deduce that this feature of its
dynamics in the enriched experimental environement has nothing to do with
the functioning of ambient phytobenthic communities, because such high
P04-P concentrations are exclusive in waters over the reef. But actually it is
not so. The reef benthos icludes rich populations of big slowly moving or
sedentary invertebrates as well as a lot of territorial fish, which live
permanently in a definite place of their bottom biotope. All these stay-athome animals excrete locally significant portions of nutrients - and of P04-P
as well. Thus its concentration in some local, especially in semi-closed zones
in which these animals like to hide, could be rather high. Therefore, the
ability of the phytobenthic communities and also of corals to consume
59
compounds of bottom biotopes have in their microstructures the autotrophic
micro- and macro algae , which consume P04-P, and the heterotrophies,
which release it (cf. Sect. 4.1). These compounds function within these
structures in a narrow coincidence, providing a semi-closed cycling of
nutrients, the same as between zooxanthellae and polyp tissues in coral.
Moreover, not only the absolute rates of Ac and Ae flows of P04-P, but
even their· ratios and the 24-h balances of P04-P coincided well in
periphyton and in the living corals, being calculated per 1 g of dry weight of
hard substrate (Table 2.5). The best coincidence was found in experiments
with the living and the dead parts of the same ramose colony, if the latter is
overgrown with the periphyton. This coincidence looks more logical if we
take into the account that the rates of photosynthesis and respiration in
living corals and in dead corals overgrown with periphyton also coincide (cf.
Sect. 4.2).
An analysis of the table shows that the flow rates of P04-P between
periphyton and water and the ratios between its consumption and release
depend upon its concentration in water. The same was shown by Atkinson
(1987). At low P04-P content, similar to the ambient ones in waters over
reefs of the Heron I. (0.1-0.3 Jlmoll- 1 ), the rate of consumption of P04-P
(Ap) by the periphyton over the piece of flat rocks and over the coral rubble
was within 1O-60JlgPkg- 1 of dry matter h- 1 . That is commensurable with
the same values in living corals (Tables 2.3, 2.5), as measured at the same
low ambient concentrations. At these low concentrations of P04-P in water
the rate of the reciprocal excretion flow (Ac) was equal to the rates of the
consumption (At) and sometimes it was even higher. In these cases, which
are usual at a low P04-P content, the net release of P04-P proceeded, and
thus the balance value At was positive (Table 2.5, Fig. 2.11). In the enriched
water, where the P04-P was 0.5-3.5Jlmol, the consumption flow in
periphytic microcosms increased up to 80-120 Jlg P kg- I h -I, while the
excretion flow was not so dependent upon the external P04-P content and
increased much less. Thus, in the enriched water consumption was 1.5-3
times more than excretion, and the net uptake of P04-P readily took place.
Thus at high P04-P concentrations the balance values At were always
negative - the periphytonic communities did not release any P04-P into the
water, but only consumed it. One could deduce that this feature of its
dynamics in the enriched experimental environement has nothing to do with
the functioning of ambient phytobenthic communities, because such high
P04-P concentrations are exclusive in waters over the reef. But actually it is
not so. The reef benthos icludes rich populations of big slowly moving or
sedentary invertebrates as well as a lot of territorial fish, which live
permanently in a definite place of their bottom biotope. All these stay-athome animals excrete locally significant portions of nutrients - and of P04-P
as well. Thus its concentration in some local, especially in semi-closed zones
in which these animals like to hide, could be rather high. Therefore, the
ability of the phytobenthic communities and also of corals to consume