Features of Ecological Morphology
297
(Schlichter 1982; Marphenin 1984; Gladfelter 1988). The nervous systems of
polyps in a colony are interconnected and thus united within a complete
system (Horridge 1956). The electrical irritation of one polyp results in
contraction of other polyps in the colony. The pulse of irritation passes
through the colony with a speed of several cm s -1. Another fact proving the
correctness of the old sentence by M. Yonge is the actual independence of
the rate of respiration of corals from the size of their polyps (cf. Sect. 9.1).
In free-living aquatic animals it is the reverse function of their size.
How important this preference for modular structure is in coral colonies
could be seen in the possibility for them to significantly increase with the aid
of this structure the light-collecting and filtering surface at the expense of
increasing their size, and branching without an increase in losses of
respiration, which remains stable as per biomass of a single module (Hughes
1983; Sorokin 1984a). The coral colonies composed of module corallites and
armed with skeletal material also have a definite preference in their ability
to regenerate, compared with free-living animals. The loss of part of from
the modules, grazed or damaged, does not cause the death of the colony,
which may quickly regenetate by the budding of the remaning modules
(Jackson 1977). The modular construction of a colony offers the possibility
of constructing from the modules a great variety of phenotypic adaptive
morphs ("living forms"), which enable the same coral species to colonize
various bottom biotopes within a wide scale of environmental conditions
(Vaughan and Wells 1993; Goreau 1963; Veron et al. 1977; Foster 1979,
1980; Vosburgh 1982; Foster 1983).
The structure of corallites has also an adaptive character and serves the
strategy of survival of the coral, connected with preferences for sources of
fedding and an acquired mechanism for shedding the sediments (Hubbard
and Pocock 1972; Hubbard 1973; Lewis and Price 1975; Foster 1980). The
diameter of polyps in colonial scleractinian corals varies within a large scale:
from 1 mm in acroporids and poritids to 3-5 cm in some mussids, and the
wet weight from 1 mg to several grams. As regards the reason for this wide
scale of sizes in polyps, it had been supposed that the corals with larger
polyps should easier catch zooplankton, thus being largely heterotrophic,
while those with small polyps (especially ramose ones) more autotrophic
(Porter 1974b; Hughes 1983). But experiments failed to prove this (Sorokin
1981a, 1984a; Gli-Turnes and Corredor 1981; cf. Sect. 9.2.1). It was shown
that the ability for photosynthesis and for heterotrophic feeding in different
species of corals, as calculated per biomass of polyps, was not very much
dependent upon the size of their polyps or on the form of their colonies.
Without refusing the definite adaptive reasons for formation of the ramose
corals with respect to enlarging their light-collecting surfaces, the main
reason for their appearance in the course of evolution seems to be quite
another. Ramose, and also cribose, corals have high mechanical endurance
of hydraulic pressure, being constructed from less calcareous skeletal
material, compared with the massive corals. This enables them to have a
297
(Schlichter 1982; Marphenin 1984; Gladfelter 1988). The nervous systems of
polyps in a colony are interconnected and thus united within a complete
system (Horridge 1956). The electrical irritation of one polyp results in
contraction of other polyps in the colony. The pulse of irritation passes
through the colony with a speed of several cm s -1. Another fact proving the
correctness of the old sentence by M. Yonge is the actual independence of
the rate of respiration of corals from the size of their polyps (cf. Sect. 9.1).
In free-living aquatic animals it is the reverse function of their size.
How important this preference for modular structure is in coral colonies
could be seen in the possibility for them to significantly increase with the aid
of this structure the light-collecting and filtering surface at the expense of
increasing their size, and branching without an increase in losses of
respiration, which remains stable as per biomass of a single module (Hughes
1983; Sorokin 1984a). The coral colonies composed of module corallites and
armed with skeletal material also have a definite preference in their ability
to regenerate, compared with free-living animals. The loss of part of from
the modules, grazed or damaged, does not cause the death of the colony,
which may quickly regenetate by the budding of the remaning modules
(Jackson 1977). The modular construction of a colony offers the possibility
of constructing from the modules a great variety of phenotypic adaptive
morphs ("living forms"), which enable the same coral species to colonize
various bottom biotopes within a wide scale of environmental conditions
(Vaughan and Wells 1993; Goreau 1963; Veron et al. 1977; Foster 1979,
1980; Vosburgh 1982; Foster 1983).
The structure of corallites has also an adaptive character and serves the
strategy of survival of the coral, connected with preferences for sources of
fedding and an acquired mechanism for shedding the sediments (Hubbard
and Pocock 1972; Hubbard 1973; Lewis and Price 1975; Foster 1980). The
diameter of polyps in colonial scleractinian corals varies within a large scale:
from 1 mm in acroporids and poritids to 3-5 cm in some mussids, and the
wet weight from 1 mg to several grams. As regards the reason for this wide
scale of sizes in polyps, it had been supposed that the corals with larger
polyps should easier catch zooplankton, thus being largely heterotrophic,
while those with small polyps (especially ramose ones) more autotrophic
(Porter 1974b; Hughes 1983). But experiments failed to prove this (Sorokin
1981a, 1984a; Gli-Turnes and Corredor 1981; cf. Sect. 9.2.1). It was shown
that the ability for photosynthesis and for heterotrophic feeding in different
species of corals, as calculated per biomass of polyps, was not very much
dependent upon the size of their polyps or on the form of their colonies.
Without refusing the definite adaptive reasons for formation of the ramose
corals with respect to enlarging their light-collecting surfaces, the main
reason for their appearance in the course of evolution seems to be quite
another. Ramose, and also cribose, corals have high mechanical endurance
of hydraulic pressure, being constructed from less calcareous skeletal
material, compared with the massive corals. This enables them to have a