Energy Balance and Specific Growth Rate of Corals
365
heterotrophic feeding were much poorer compared with those in hermatypic
scleractinians. Under similar experimental conditions the latter much more
efficiently fed on either zooplankton, bacteria, of DOM. This corresponds
to a more developed morphology in scleractinian polyps, compared with
that in octocorals. The above data enable us to suppose that the high ability
of octocorals to compete with scleractinian corals in reef benthic
communities could be based mostly on their chemical defence capacity and
on their high growth rate, rather than on their trophic activity or on their
trophic opportunism in relation to sources of heterotrophic feeding.
9.3 Energy Balance and Specific Growth Rate of Corals
The shares of autotrophic and heterotrophic nutrition of corals in their
energy balance is one of the main questions of their ecophysiology
(Muscatine 1980). Many observations have proved the point that hermatypic
corals may completely satisfy their energy and growth needs by means of the
autotrophic production of their zooxanthellae. For example, kept in the
light they survived for months in water deprived of plankton by filtration
(Franziskett 1970). Corals may live inside large sponges in water completely
cleaned of any suspended matter by the filtering activity of their hosts
(Porter 1974b), Corals isolated from light by being covered in situ with black
plastic film died or bleached (Rogers 1979b). Their photosynthetic
production in diurnal balance exceeds respiration (Pt/Mt > 1). And
nevertheless, the above facts in the coral's life could not be accepted as a
proof of purely autotrophic nutrition of hermatypic corals. On the one hand,
their polyps cannot use all the autotrophic production of zooxanthellae, but
only its translocated part. On the other hand, respiration is only a part of
their energy credit, moreover the Pt/Mt ratio in corals drops down below 1
in shadowed or deep biotopes in spite of their light adaptation (Drew 1973).
Thus, in these biotopes the share of heterotrophic sources of nutrition in
their energy balance should be compellibly significant. Our calculations,
based upon the assumption that corals spend on their respiration -60% of
their total energy expenditure, and also on the average shares of various
food sources in the coral's nutrition (see above), resulted in the following
evaluation of the components in the energy debet in coral communities of
the shallow areas of the Heron Island reef: 70% photosynthesis of symbiotic
zooxanthellae, 20% predation, and 10% feeding on DOM and on
bacterioplankton. According to Lewis (1981), zooxanthellae provide around
65% of the energy debet in hermatypic corals.
Another approach to this problem could be the calculations of CZAR -
the share of translocated autotrophic production of zooxanthellae in the
respiration of the polyp's animal tissues: CZAR = [(Pnz · T)/Mal%
(Muscatine et al. 1985; see Sects. 8.3, 9.1). The index Pnz in the above
365
heterotrophic feeding were much poorer compared with those in hermatypic
scleractinians. Under similar experimental conditions the latter much more
efficiently fed on either zooplankton, bacteria, of DOM. This corresponds
to a more developed morphology in scleractinian polyps, compared with
that in octocorals. The above data enable us to suppose that the high ability
of octocorals to compete with scleractinian corals in reef benthic
communities could be based mostly on their chemical defence capacity and
on their high growth rate, rather than on their trophic activity or on their
trophic opportunism in relation to sources of heterotrophic feeding.
9.3 Energy Balance and Specific Growth Rate of Corals
The shares of autotrophic and heterotrophic nutrition of corals in their
energy balance is one of the main questions of their ecophysiology
(Muscatine 1980). Many observations have proved the point that hermatypic
corals may completely satisfy their energy and growth needs by means of the
autotrophic production of their zooxanthellae. For example, kept in the
light they survived for months in water deprived of plankton by filtration
(Franziskett 1970). Corals may live inside large sponges in water completely
cleaned of any suspended matter by the filtering activity of their hosts
(Porter 1974b), Corals isolated from light by being covered in situ with black
plastic film died or bleached (Rogers 1979b). Their photosynthetic
production in diurnal balance exceeds respiration (Pt/Mt > 1). And
nevertheless, the above facts in the coral's life could not be accepted as a
proof of purely autotrophic nutrition of hermatypic corals. On the one hand,
their polyps cannot use all the autotrophic production of zooxanthellae, but
only its translocated part. On the other hand, respiration is only a part of
their energy credit, moreover the Pt/Mt ratio in corals drops down below 1
in shadowed or deep biotopes in spite of their light adaptation (Drew 1973).
Thus, in these biotopes the share of heterotrophic sources of nutrition in
their energy balance should be compellibly significant. Our calculations,
based upon the assumption that corals spend on their respiration -60% of
their total energy expenditure, and also on the average shares of various
food sources in the coral's nutrition (see above), resulted in the following
evaluation of the components in the energy debet in coral communities of
the shallow areas of the Heron Island reef: 70% photosynthesis of symbiotic
zooxanthellae, 20% predation, and 10% feeding on DOM and on
bacterioplankton. According to Lewis (1981), zooxanthellae provide around
65% of the energy debet in hermatypic corals.
Another approach to this problem could be the calculations of CZAR -
the share of translocated autotrophic production of zooxanthellae in the
respiration of the polyp's animal tissues: CZAR = [(Pnz · T)/Mal%
(Muscatine et al. 1985; see Sects. 8.3, 9.1). The index Pnz in the above