362
Nutrition of Corals
reaction of the other polyps increases the probability of the neighbouring
polyps catching also food accidentally.
The participation of mucus in the processes of feeding in octocorals
remains disputable (Lewis 1982). But actually Xenia and some other
symbiotic alcyonaceans are definitely able to excrete mucus. We have
observed the following way of hunting the preys, early nauplii of artemia, by
polyps of Sarcophyton. The prey, which is swimming in the vicinity of
colony, when caught in the mucus net stretched out by the polyp, starts to
move chaotically winding so around its body the mucus stripe, and thus
inevitably approaching the place where this stripe originates, i.e., the mouth
of the polyp. The process of digestion of food in octocorals is similar to that
in other Anthozoa, but lasts two to three times longer, probably because of
reduced mesenterial filaments in them. The artemia nauplii swallowed were
digested by polyps of Sarcophyton only in 10-12 h (Lewis 1982).
Quantitative evaluations of feeding rats in octocorals have been recently
missing. Semiquantitative estimations of the gut contents in polyps of some
octocoral species were made by Lewis (1982). The amounts of artemia cysts
or sephadex particles soaked in broth swallowed by them were also
estimated (Lasker 1981; Lasker et al. 1983), and the decrease in the number
of artemia nauplii in aquaria in the presence of gorgonian colonies was
observed as well (Leversee 1976). These data have the slackness of their
activity as predators. So they hardly could acquire enough energy this way.
But at least the asymbiotic octocorals have to get all the necessary nutrition
by heterotrophy only. This situation suggested the proposition that just
sedimentary filtration of microplankton and other suspended matter, but not
predation might be the main mechanism of nutrition in octocorals (Mariscal
and Bigger 1977; Lasker 1981). Therefore, when we have started our study
of the quantitative aspects of octocoral nutrition we also supposed the latter
assumption as being the most probable. In our study we have used as
labeled animal food the nauplii of artemia, the veligers of Aplysia, the
rotifers Brachionus and the ciliates Strombidium. As particulated food,
suspensions of labeled algae Isochrysis and marine Chlorella were used, as
well as labeled bacterioplankton. The experiments were performed with the
most common octocorals of the Indo-Pacific. For comparison of feeding in
octocorals and scleractinians in the same experiments, the hermatypic
scleractinian coral Stylophora pistillata and the ahermatypic species
Tubastrea were also used. As DOM, labeled protein hydrolizate was
employed.
The results showed that different species of symbiotic octocorals may
ingest practically all kinds of food offered them but to different degrees
(Table 9.19; Fig. 9.7). When feeding on zooplankton, the symbiotic
octocorals might acquire up to 30% of their total energy demand (A/MG).
The assumption on their ability to feed on the microzooplankton was not
proved (Table 9.20). The rates of their feeding on veligers, rotifers and
ciliates were rather low: A/MG ratios were in this case only 1-5%. Among
Nutrition of Corals
reaction of the other polyps increases the probability of the neighbouring
polyps catching also food accidentally.
The participation of mucus in the processes of feeding in octocorals
remains disputable (Lewis 1982). But actually Xenia and some other
symbiotic alcyonaceans are definitely able to excrete mucus. We have
observed the following way of hunting the preys, early nauplii of artemia, by
polyps of Sarcophyton. The prey, which is swimming in the vicinity of
colony, when caught in the mucus net stretched out by the polyp, starts to
move chaotically winding so around its body the mucus stripe, and thus
inevitably approaching the place where this stripe originates, i.e., the mouth
of the polyp. The process of digestion of food in octocorals is similar to that
in other Anthozoa, but lasts two to three times longer, probably because of
reduced mesenterial filaments in them. The artemia nauplii swallowed were
digested by polyps of Sarcophyton only in 10-12 h (Lewis 1982).
Quantitative evaluations of feeding rats in octocorals have been recently
missing. Semiquantitative estimations of the gut contents in polyps of some
octocoral species were made by Lewis (1982). The amounts of artemia cysts
or sephadex particles soaked in broth swallowed by them were also
estimated (Lasker 1981; Lasker et al. 1983), and the decrease in the number
of artemia nauplii in aquaria in the presence of gorgonian colonies was
observed as well (Leversee 1976). These data have the slackness of their
activity as predators. So they hardly could acquire enough energy this way.
But at least the asymbiotic octocorals have to get all the necessary nutrition
by heterotrophy only. This situation suggested the proposition that just
sedimentary filtration of microplankton and other suspended matter, but not
predation might be the main mechanism of nutrition in octocorals (Mariscal
and Bigger 1977; Lasker 1981). Therefore, when we have started our study
of the quantitative aspects of octocoral nutrition we also supposed the latter
assumption as being the most probable. In our study we have used as
labeled animal food the nauplii of artemia, the veligers of Aplysia, the
rotifers Brachionus and the ciliates Strombidium. As particulated food,
suspensions of labeled algae Isochrysis and marine Chlorella were used, as
well as labeled bacterioplankton. The experiments were performed with the
most common octocorals of the Indo-Pacific. For comparison of feeding in
octocorals and scleractinians in the same experiments, the hermatypic
scleractinian coral Stylophora pistillata and the ahermatypic species
Tubastrea were also used. As DOM, labeled protein hydrolizate was
employed.
The results showed that different species of symbiotic octocorals may
ingest practically all kinds of food offered them but to different degrees
(Table 9.19; Fig. 9.7). When feeding on zooplankton, the symbiotic
octocorals might acquire up to 30% of their total energy demand (A/MG).
The assumption on their ability to feed on the microzooplankton was not
proved (Table 9.20). The rates of their feeding on veligers, rotifers and
ciliates were rather low: A/MG ratios were in this case only 1-5%. Among