340
Nutrition of Corals
illuminated with a flash light a part of the coral colony. To study the
spectrum of feeding, this author extracted in situ the contents of the gastral
cavity of polyps, inserting the needle of a syringe through their mouths. The
function of cilia and mucus filaments in the capturing of particulated food
was studied by using the suspension of heavy particles of corund (Y onge
1930b). The rate of sedimentary filter feeding of corals was studied by
recording the decrease in concentration of food particles or neutral particles
in the presence of corals (Roushdy and Hansen 1961; Lewis 1976). But this
method cannot yield really reliable information about the rate of feeding of
corals, because in this case the amount of the suspended matter actually
swallowed by polyps, remains unknown.
Really quantitative data on the feeding of corals could be most reliably
obtained with the aid of radioisotopic labels. For the labeling of the
potential food of corals the isotopes of sulfur 35S and of tritium 3H were
used (Di Salvo 1971a; Coffroth 1984). But the most convenient and reliable
label could be made using the radiocarbon 14c. This radioisotope has been
employed for the establishing of location of assimilated labeled food
material within the polyp's body with the aid of radioautography (Goreau
and Goreau 1960b). The radiocarbon method of quantitative study of
feeding of aquatic animals (Sorokin, 1968) have been used by us also for the
study of different aspects of the heterotrophic feeding of corals of the GBR,
of reefs of the Indian Ocean and of the South China Sea (Sorokin 1978b,
1981c). As labeled food were used: dissolved organic matter (DOM) protein
hydrolizate from labeled planktonic algae, bacterioplankton, labeled with
the aid of this hydrolizate, and various labeled forms of zooplankton. The
zooplankters: ciliates, veligers, rotifers, of nauplii of artemia were marked
through feeding them with labeled food - bacteria or microalgae (Sorokin
1984a). The veligers were obtained by hatching eggs of the nudibranch
mollusc Aplysia. To induce their spawning, we injected them with KCI, or
serotonin solutions. Corals, selected for the feeding experiments, were first
adapted to the experimental conditions. The labeled food was added at
night only if their polyps were opened.
9.2.1 Feeding of Scleractinian Corals
In their hunting for animal prey scleractinian corals use the ways known in
other sessile coelenterata. They may capture prey with their tentacles armed
with the powerful cnidocil. The preys are immobilized by being hit by
poisonous cnidae. Then they are captured by the tentacles and transferred
to the mouth. The preys could be captured and immobilized also with the
aid of mucus nets, formed by the polyps. Both these mechanisms interact
during hunting (Yonge 1930b, 1940; Goreau et al. 1971). The activity of
polyps is stimulated by amino acids which the zooplankters excrete. The
polyp "feels" the presence of the prey and, stimulated, starts in pursuit with
Nutrition of Corals
illuminated with a flash light a part of the coral colony. To study the
spectrum of feeding, this author extracted in situ the contents of the gastral
cavity of polyps, inserting the needle of a syringe through their mouths. The
function of cilia and mucus filaments in the capturing of particulated food
was studied by using the suspension of heavy particles of corund (Y onge
1930b). The rate of sedimentary filter feeding of corals was studied by
recording the decrease in concentration of food particles or neutral particles
in the presence of corals (Roushdy and Hansen 1961; Lewis 1976). But this
method cannot yield really reliable information about the rate of feeding of
corals, because in this case the amount of the suspended matter actually
swallowed by polyps, remains unknown.
Really quantitative data on the feeding of corals could be most reliably
obtained with the aid of radioisotopic labels. For the labeling of the
potential food of corals the isotopes of sulfur 35S and of tritium 3H were
used (Di Salvo 1971a; Coffroth 1984). But the most convenient and reliable
label could be made using the radiocarbon 14c. This radioisotope has been
employed for the establishing of location of assimilated labeled food
material within the polyp's body with the aid of radioautography (Goreau
and Goreau 1960b). The radiocarbon method of quantitative study of
feeding of aquatic animals (Sorokin, 1968) have been used by us also for the
study of different aspects of the heterotrophic feeding of corals of the GBR,
of reefs of the Indian Ocean and of the South China Sea (Sorokin 1978b,
1981c). As labeled food were used: dissolved organic matter (DOM) protein
hydrolizate from labeled planktonic algae, bacterioplankton, labeled with
the aid of this hydrolizate, and various labeled forms of zooplankton. The
zooplankters: ciliates, veligers, rotifers, of nauplii of artemia were marked
through feeding them with labeled food - bacteria or microalgae (Sorokin
1984a). The veligers were obtained by hatching eggs of the nudibranch
mollusc Aplysia. To induce their spawning, we injected them with KCI, or
serotonin solutions. Corals, selected for the feeding experiments, were first
adapted to the experimental conditions. The labeled food was added at
night only if their polyps were opened.
9.2.1 Feeding of Scleractinian Corals
In their hunting for animal prey scleractinian corals use the ways known in
other sessile coelenterata. They may capture prey with their tentacles armed
with the powerful cnidocil. The preys are immobilized by being hit by
poisonous cnidae. Then they are captured by the tentacles and transferred
to the mouth. The preys could be captured and immobilized also with the
aid of mucus nets, formed by the polyps. Both these mechanisms interact
during hunting (Yonge 1930b, 1940; Goreau et al. 1971). The activity of
polyps is stimulated by amino acids which the zooplankters excrete. The
polyp "feels" the presence of the prey and, stimulated, starts in pursuit with