344
Nutrition of Corals
polyps of the coral Montastrea digest the artemia nauplii in 1.5-2 h. But the
time of digestion of large preys or pieces of meat swallowed by the polyp
could be much longer - up to 1O-12h. We have estimated the time of
digestion of labeled artemia nauplii. Corals were fed during 10 min with
these preys. Then they were transferred into the beakers with unlabeled
food, and the time of appearance of labeled particles of undigested remains
of food was recorded. The results of the experiments showed that corals
with large polyps digest the preys in 2-2.5 h, and corals with a small polyps
in 2.5-3 h. The assimilability of the animal preys ingested by polyps, as
estimated by the radiocarbon method in experiments with different corals,
appears to be high: 70-80% (Table 9.12).
Scleractinian corals were shown to be capable of sedimentary filter
feeding. They may filter out from the water column planktonic bacteria (Di
Salvo 1971a, 1973; Sorokin 1971b, 1973c, 1978b), pseudoplankton and
detritus (Lewis and Price 1975, 1976) and even the neutral particles, like
suspended graphite (Lewis 1977a). Filtration proceeds by the interaction of
ciliar currents over the polyp with the mucus nets, as described above. The
particles contained in water passing through the mucus net or over the
mucus strips stick to the latter's surface. In this process a definite role is
played by electrostatic forces. The mucus substance contains amino groups,
charged positively, while the mice lis of colloids, the bacterial cells or the
detritus particles, are charged most often negatively, having on their surface
the radicals of carbonic acids. The filtering mechanism in corals works
permanently around the clock independently of the state of the coral,
whether active and expanded or passive, hidden inside the corallite and
closed. Even when closed, the polyps emit the strips of mucus from their
mouths, and the automatically working ciliar apparatus makes at their ends
the mucus nets (Coles and Strathmann 1973). The particulated matter thus
caught is gradually accumulated on them. If it does not contain enough
nutritive substance, the mucus nets overloaded by it are driven out from the
polyp by ciliar currents thus cleaning its surface. But if the mucus net has
caught something edible, the "feeding reaction" of the polyp is triggered, as
described above, the polyp ingests food caught together with mucus. The
polyps can manifest the "food reaction" also in closed inactive state.
Corals using this mechanism most actively include Montastrea, Mussa,
Diploria, Colpophyllia, Lobophyllia, Hydnophora, Pavona, and Acropora.
But some corals, like Pocillopora or Porites, which were proved to be
capable of filter feeding on the bacterioplankton, did not form mucus nets at
all. The flakes of mucus they excrete is used to immobilize the preys caught
and to relieve the process of swallowing (Abe 1938). These corals use a
different mechanism of sedimentary feeding on suspended food. Their ciliar
currents are directed from the coenosarc to the tentacles and to the mouth,
but not backward as in other corals using the mucus nets. These currents
bring the particulated matter from outside to their oral disc where it is
caught stuck to the mucus flakes, which form lumps. If they have enough
Nutrition of Corals
polyps of the coral Montastrea digest the artemia nauplii in 1.5-2 h. But the
time of digestion of large preys or pieces of meat swallowed by the polyp
could be much longer - up to 1O-12h. We have estimated the time of
digestion of labeled artemia nauplii. Corals were fed during 10 min with
these preys. Then they were transferred into the beakers with unlabeled
food, and the time of appearance of labeled particles of undigested remains
of food was recorded. The results of the experiments showed that corals
with large polyps digest the preys in 2-2.5 h, and corals with a small polyps
in 2.5-3 h. The assimilability of the animal preys ingested by polyps, as
estimated by the radiocarbon method in experiments with different corals,
appears to be high: 70-80% (Table 9.12).
Scleractinian corals were shown to be capable of sedimentary filter
feeding. They may filter out from the water column planktonic bacteria (Di
Salvo 1971a, 1973; Sorokin 1971b, 1973c, 1978b), pseudoplankton and
detritus (Lewis and Price 1975, 1976) and even the neutral particles, like
suspended graphite (Lewis 1977a). Filtration proceeds by the interaction of
ciliar currents over the polyp with the mucus nets, as described above. The
particles contained in water passing through the mucus net or over the
mucus strips stick to the latter's surface. In this process a definite role is
played by electrostatic forces. The mucus substance contains amino groups,
charged positively, while the mice lis of colloids, the bacterial cells or the
detritus particles, are charged most often negatively, having on their surface
the radicals of carbonic acids. The filtering mechanism in corals works
permanently around the clock independently of the state of the coral,
whether active and expanded or passive, hidden inside the corallite and
closed. Even when closed, the polyps emit the strips of mucus from their
mouths, and the automatically working ciliar apparatus makes at their ends
the mucus nets (Coles and Strathmann 1973). The particulated matter thus
caught is gradually accumulated on them. If it does not contain enough
nutritive substance, the mucus nets overloaded by it are driven out from the
polyp by ciliar currents thus cleaning its surface. But if the mucus net has
caught something edible, the "feeding reaction" of the polyp is triggered, as
described above, the polyp ingests food caught together with mucus. The
polyps can manifest the "food reaction" also in closed inactive state.
Corals using this mechanism most actively include Montastrea, Mussa,
Diploria, Colpophyllia, Lobophyllia, Hydnophora, Pavona, and Acropora.
But some corals, like Pocillopora or Porites, which were proved to be
capable of filter feeding on the bacterioplankton, did not form mucus nets at
all. The flakes of mucus they excrete is used to immobilize the preys caught
and to relieve the process of swallowing (Abe 1938). These corals use a
different mechanism of sedimentary feeding on suspended food. Their ciliar
currents are directed from the coenosarc to the tentacles and to the mouth,
but not backward as in other corals using the mucus nets. These currents
bring the particulated matter from outside to their oral disc where it is
caught stuck to the mucus flakes, which form lumps. If they have enough