Heterotrophic Feeding of Corals
345
edible material, the "food reaction" starts and it is swallowed, if not it is
rejected and drops off the polyp. And other way of sedimentary feeding in
these corals is the digestion of food particles settled on or stuck to the
surface of the expanded polyp body by proteases secreted by the cells of
their epithelium. The polypeptides thus formed are phagocytosed by the
wandering cells (Tiffon and Bouillon 1975). The epithelial cells of the polyp
are apparently able to absorb the cells of bacterioplankton settled on its
surface via pinocytosis. Indeed, their surface is covered by numerous
invaginations of the cell wall, which were proved to be functionally capable
of pinocyctosis (Goreau and Philpott 1956; Goreau et al. 1971).
The ability of corals to take up dissolved organic matter (DOM) was first
recorded by T. and N. Goreau (Gore au and Goreau 1960a) and by Stephens
(1962). It was supposed that an extremely vigorous consumption of DOM by
corals could be accomplished only by the active enzyme transport with
participation of the permease mechanisms (Goreau et al. 1971). Later, we
have proved it by direct experiments (Sorokin 1977b, 1986a). The
nutritional behavior in most corals is characterized by the alternation of the
periods of relaxation, when the polyps are closed and hidden in corallites,
and the periods of activity, when they are opened and expanded over the
corallites (Yonge 1930b; Glynn 1973b; Porter 1974b; Lewis and Price 1975;
Sebens and de Riemer 1977). The adaptive reason behind this type of
behavior could be seen in the corals' economy with living resources during
the daytime period, when the zooplankton in reef waters is very scarce,
being hidden in bottom biotopes (d. Sect. 3.3.2). In fact, their respiration at
this stage of relaxation is slower than during the period of activity
(Roffmann 1968; Sebens and de Riemer 1977). At the same time, the
photosynthesis of polyps during the inactive phase of the diurnal cycle does
not decrease, and their activity as the filter feeders is preserved as well
(Lewis and Price 1975). There are also, proofs of corals being most active in
their predatory feeding at dusk, at dawn (~75% of total preys ingested) and
during the night time (Glynn 1973b; Porter 1976). The diurnal rhythm of
activity varies in different taxa of corals. Groups of species which are active
only at night are the most numerous. They include corals with large-toaverage sizes of polyps, which readily feed on zooplankton, using for
hunting both the tentacles and the mucus nets. Their nocturnal activity
seems to be directly connected with their success in predatory feeding.
Among the corals which are active diurnally the ramose corals Pocillopora,
Stylophora and some species of Porites and Acropora could be mentioned
(Table 9.10). The diurnal rhythm in corals seems to be controlled by the
level of illumination (Swenney 1976).
We have tried to obtain a quantitative expression of the diurnal activity in
various corals by measuring in experiments the ratios of their predatory
feeding at midday and midnight. The food was labeled with 14C nauplii of
Artemia (Table 9.11). The results showed that even corals with small polyps,
which were active also in the daytime (Pocillopora, Stylophora, Acropora
345
edible material, the "food reaction" starts and it is swallowed, if not it is
rejected and drops off the polyp. And other way of sedimentary feeding in
these corals is the digestion of food particles settled on or stuck to the
surface of the expanded polyp body by proteases secreted by the cells of
their epithelium. The polypeptides thus formed are phagocytosed by the
wandering cells (Tiffon and Bouillon 1975). The epithelial cells of the polyp
are apparently able to absorb the cells of bacterioplankton settled on its
surface via pinocytosis. Indeed, their surface is covered by numerous
invaginations of the cell wall, which were proved to be functionally capable
of pinocyctosis (Goreau and Philpott 1956; Goreau et al. 1971).
The ability of corals to take up dissolved organic matter (DOM) was first
recorded by T. and N. Goreau (Gore au and Goreau 1960a) and by Stephens
(1962). It was supposed that an extremely vigorous consumption of DOM by
corals could be accomplished only by the active enzyme transport with
participation of the permease mechanisms (Goreau et al. 1971). Later, we
have proved it by direct experiments (Sorokin 1977b, 1986a). The
nutritional behavior in most corals is characterized by the alternation of the
periods of relaxation, when the polyps are closed and hidden in corallites,
and the periods of activity, when they are opened and expanded over the
corallites (Yonge 1930b; Glynn 1973b; Porter 1974b; Lewis and Price 1975;
Sebens and de Riemer 1977). The adaptive reason behind this type of
behavior could be seen in the corals' economy with living resources during
the daytime period, when the zooplankton in reef waters is very scarce,
being hidden in bottom biotopes (d. Sect. 3.3.2). In fact, their respiration at
this stage of relaxation is slower than during the period of activity
(Roffmann 1968; Sebens and de Riemer 1977). At the same time, the
photosynthesis of polyps during the inactive phase of the diurnal cycle does
not decrease, and their activity as the filter feeders is preserved as well
(Lewis and Price 1975). There are also, proofs of corals being most active in
their predatory feeding at dusk, at dawn (~75% of total preys ingested) and
during the night time (Glynn 1973b; Porter 1976). The diurnal rhythm of
activity varies in different taxa of corals. Groups of species which are active
only at night are the most numerous. They include corals with large-toaverage sizes of polyps, which readily feed on zooplankton, using for
hunting both the tentacles and the mucus nets. Their nocturnal activity
seems to be directly connected with their success in predatory feeding.
Among the corals which are active diurnally the ramose corals Pocillopora,
Stylophora and some species of Porites and Acropora could be mentioned
(Table 9.10). The diurnal rhythm in corals seems to be controlled by the
level of illumination (Swenney 1976).
We have tried to obtain a quantitative expression of the diurnal activity in
various corals by measuring in experiments the ratios of their predatory
feeding at midday and midnight. The food was labeled with 14C nauplii of
Artemia (Table 9.11). The results showed that even corals with small polyps,
which were active also in the daytime (Pocillopora, Stylophora, Acropora