360
Nutrition of Corals
Heteroxenia was proved to digest the zooxanthellae extruded by polyps into
their gastral cavity (Schlichter 1982). This author demonstrated also the
ability of this alcyonacean to feed on DOM. Coffroth (1984) proved an
important role of the mucus excreted by invertebrates (largely by corals), as
food for some octocorals. In her experiments the gorgonian Plexaura porosa
could compensate energy expenditurs by feeding only on mucus of
scleractinian corals.
In his study on nutrition of a variety of octo corals Lewis (1982) offered
them various kinds of zooplankton, and also investigated the gut contents of
polyps in specimens taken at the reef and immediately inspected. He established that among the 24 species thus checked some did not catch any animal
preys under experimental conditions. Among them were the symbiotic
species Sinularia capillosa, Eunicea to urneforti , Paralemnalia digitiformis,
Plexaura flexuosa, and Gorgonia ventalina. The same was valid for the
xeniids. Nevertheless, when analyzing the guts in xeniid specimens caught in
nature he found in some of them planktonic crustaceans, small polychaetes,
veligers, and eggs of invertebrates. Probably, to catch food the polyps of
xeniids need to be kept permanently in motion by waves on the shallows
where they are living. Other octocorals studied, both their symbiotic species
and genera (Lobophytum, Sarcophyton, Sinularia densa, Capnella, Lemnalia,
Isis, Juncella, Pseudopterogorgia, Plexaura, Telesto, Tubipora) , and the
asymbiotic ones (Dendronephthea, Rumphella, Briareum, Muriceopsis,
Gorgonia) were observed catching and swallowing the planktonic crustaceams and veligers.
With a view to the variability of feeding strategy in different taxa of
octocorals, we have investigated the spectrum of feeding in a selection of
coral species, which inhabit reefs in the Indian Ocean and the GBR,
employing the radiocarbon method. To the specimens of corals acclimated
to experimental conditions various kinds of labeled food were offered
excluding so the influence of their physiological state on the results of the
experiments. The typical results are given in Fig. 9.7. In general, they
proved the basic conclusion on the ability of most octocorals for predatory
feeding. Second in importance among the sources of their feeding were the
bacterioplankton and DOM. The most active predators among the
octocorals tested were their asymbiotic species Dendronephthea, Spongotes,
Bebryce, Acabaria. The gorgonian Mopsella was found to be feeding also on
phytoplankton.
Being more ancient and primitive in their morphology, compared with
scleractinians, the octocorals use also more primitive and quite different
mechanisms of catching their preys or food particles. They employ mostly
direct mechanical seizure of the prey with their motile tentacles, armed by
pinnules at the edges. The pinnules enlarge the catching surface of the
whole bunch of tentacles. The reaction of the tentacles is very swift, being
triggered by tactile contact of the prey with the tentacle or pinnules. Thus
the polyps grab not only moving preys but also immobile passively floating
Nutrition of Corals
Heteroxenia was proved to digest the zooxanthellae extruded by polyps into
their gastral cavity (Schlichter 1982). This author demonstrated also the
ability of this alcyonacean to feed on DOM. Coffroth (1984) proved an
important role of the mucus excreted by invertebrates (largely by corals), as
food for some octocorals. In her experiments the gorgonian Plexaura porosa
could compensate energy expenditurs by feeding only on mucus of
scleractinian corals.
In his study on nutrition of a variety of octo corals Lewis (1982) offered
them various kinds of zooplankton, and also investigated the gut contents of
polyps in specimens taken at the reef and immediately inspected. He established that among the 24 species thus checked some did not catch any animal
preys under experimental conditions. Among them were the symbiotic
species Sinularia capillosa, Eunicea to urneforti , Paralemnalia digitiformis,
Plexaura flexuosa, and Gorgonia ventalina. The same was valid for the
xeniids. Nevertheless, when analyzing the guts in xeniid specimens caught in
nature he found in some of them planktonic crustaceans, small polychaetes,
veligers, and eggs of invertebrates. Probably, to catch food the polyps of
xeniids need to be kept permanently in motion by waves on the shallows
where they are living. Other octocorals studied, both their symbiotic species
and genera (Lobophytum, Sarcophyton, Sinularia densa, Capnella, Lemnalia,
Isis, Juncella, Pseudopterogorgia, Plexaura, Telesto, Tubipora) , and the
asymbiotic ones (Dendronephthea, Rumphella, Briareum, Muriceopsis,
Gorgonia) were observed catching and swallowing the planktonic crustaceams and veligers.
With a view to the variability of feeding strategy in different taxa of
octocorals, we have investigated the spectrum of feeding in a selection of
coral species, which inhabit reefs in the Indian Ocean and the GBR,
employing the radiocarbon method. To the specimens of corals acclimated
to experimental conditions various kinds of labeled food were offered
excluding so the influence of their physiological state on the results of the
experiments. The typical results are given in Fig. 9.7. In general, they
proved the basic conclusion on the ability of most octocorals for predatory
feeding. Second in importance among the sources of their feeding were the
bacterioplankton and DOM. The most active predators among the
octocorals tested were their asymbiotic species Dendronephthea, Spongotes,
Bebryce, Acabaria. The gorgonian Mopsella was found to be feeding also on
phytoplankton.
Being more ancient and primitive in their morphology, compared with
scleractinians, the octocorals use also more primitive and quite different
mechanisms of catching their preys or food particles. They employ mostly
direct mechanical seizure of the prey with their motile tentacles, armed by
pinnules at the edges. The pinnules enlarge the catching surface of the
whole bunch of tentacles. The reaction of the tentacles is very swift, being
triggered by tactile contact of the prey with the tentacle or pinnules. Thus
the polyps grab not only moving preys but also immobile passively floating