322
Morphology and Ecological Physiology of Corals
best "chemists" among Anthozoa are the octocorals and the zoantharians.
Most of them do not possess a hard exoskeleton, which could protect them
from grazing. In the octocorals moreover the cnidocil is drastically reduced,
and so it cannot be used for defense or for interspecific aggression, as
scleractinians or hydrocorals use it.
The means of chemical defense and aggression used by octocorals are
numerous and varied. They embrace a wide spectrum of antibiotic, as well
as terpenoid and lipoid toxic and biologically active substances, including
extremely active metabolites, such as prostaglandins. The antibacterial
action of octocorals was discovered when pieces of their colonies had been
placed on agar plates, infected by the test bacteria (Burkholder 1973), thus
producing sterile zones. It was found that the colonies most active in this
respect, gorgonaceans Pseudoplexaura crassa and Eunicea mammosa,
contain the lactones crassin and mammosin, which resemble certain
components of penicillin (Cieresko 1962). These substances have an
antibacterial effect and seem to be toxic also for fish, thus accomplishing a
double function: preserving the gorgonaceans from fouling and repelling
their predators. The gorgonians excrete anti algal agents, which prevent their
fouling with microalgae (Targett et al. 1983). The numerous terpenoid
compounds produced by most octocorals have also definite antimicrobial
properties. The antibiotic defense of octocorals against their fouling by
bacteria is moreover for most of them important, because they do not
actually produce mucus, which accomplishes this function in scleractinians.
The colonies of corals are soaked with protective structural lipids, like
high-molecular-weight alcohols, sterols, glyceric esters, prostaglandins, waxlike substances and hydrocarbons (Bergmann 1962; Cieresko et al. 1968).
They comprise as mush as 10 to 30% of their total biomass. The steroid
lipids (including cholesterines) and the waxes of cethylpalmitate type are
present in the lipoid fractions of most corals, in octocorals, zoantharians and
scleractinians (King and Bergmann 1942; Cieresko and Karns 1973;
Kanazawa et al. 1976; Benson et al. 1978). These structural lipoids have a
revolting taste. Some of them are even poisonous. They are also indigestible
for most predators except Acanthaster and some fish (Benson et al. 1978).
So they perform the function of peserving corals from grazing. And, in fact,
corals and zoantharians are eaten only by a few highly specialized members
of reef fauna.
The prostaglandins have been discovered in the lipoid fraction of the
Atlantic gorgonian Plexaura homomalla (Weinheimer and Spraggins 1969;
Bayer and Weinheimer 1974). These biologically active compounds were
first isolated from sheep's testis. They exert strong polyvalent action upon
the blood pressure, the muscular and nervous system, and the growth of
warm-blooded animals, when injected into their blood-stream in negligible
amounts of a few Ilg kg -I of their weight. Prostaglandins are now widely
used in medicine and in agriculture (Pike 1974). The lipoid fraction of this
gorgonian contains an enormous amount of this valuable substance - up to
Morphology and Ecological Physiology of Corals
best "chemists" among Anthozoa are the octocorals and the zoantharians.
Most of them do not possess a hard exoskeleton, which could protect them
from grazing. In the octocorals moreover the cnidocil is drastically reduced,
and so it cannot be used for defense or for interspecific aggression, as
scleractinians or hydrocorals use it.
The means of chemical defense and aggression used by octocorals are
numerous and varied. They embrace a wide spectrum of antibiotic, as well
as terpenoid and lipoid toxic and biologically active substances, including
extremely active metabolites, such as prostaglandins. The antibacterial
action of octocorals was discovered when pieces of their colonies had been
placed on agar plates, infected by the test bacteria (Burkholder 1973), thus
producing sterile zones. It was found that the colonies most active in this
respect, gorgonaceans Pseudoplexaura crassa and Eunicea mammosa,
contain the lactones crassin and mammosin, which resemble certain
components of penicillin (Cieresko 1962). These substances have an
antibacterial effect and seem to be toxic also for fish, thus accomplishing a
double function: preserving the gorgonaceans from fouling and repelling
their predators. The gorgonians excrete anti algal agents, which prevent their
fouling with microalgae (Targett et al. 1983). The numerous terpenoid
compounds produced by most octocorals have also definite antimicrobial
properties. The antibiotic defense of octocorals against their fouling by
bacteria is moreover for most of them important, because they do not
actually produce mucus, which accomplishes this function in scleractinians.
The colonies of corals are soaked with protective structural lipids, like
high-molecular-weight alcohols, sterols, glyceric esters, prostaglandins, waxlike substances and hydrocarbons (Bergmann 1962; Cieresko et al. 1968).
They comprise as mush as 10 to 30% of their total biomass. The steroid
lipids (including cholesterines) and the waxes of cethylpalmitate type are
present in the lipoid fractions of most corals, in octocorals, zoantharians and
scleractinians (King and Bergmann 1942; Cieresko and Karns 1973;
Kanazawa et al. 1976; Benson et al. 1978). These structural lipoids have a
revolting taste. Some of them are even poisonous. They are also indigestible
for most predators except Acanthaster and some fish (Benson et al. 1978).
So they perform the function of peserving corals from grazing. And, in fact,
corals and zoantharians are eaten only by a few highly specialized members
of reef fauna.
The prostaglandins have been discovered in the lipoid fraction of the
Atlantic gorgonian Plexaura homomalla (Weinheimer and Spraggins 1969;
Bayer and Weinheimer 1974). These biologically active compounds were
first isolated from sheep's testis. They exert strong polyvalent action upon
the blood pressure, the muscular and nervous system, and the growth of
warm-blooded animals, when injected into their blood-stream in negligible
amounts of a few Ilg kg -I of their weight. Prostaglandins are now widely
used in medicine and in agriculture (Pike 1974). The lipoid fraction of this
gorgonian contains an enormous amount of this valuable substance - up to