Ecological Biochemistry of Corals
323
15%. Its content represents in colonies of Plexaura up to 5-8% of their dry
weight, which is 10 7 times more than in tissues of other animals, and by an
order more than in sheep testis, from which it is usually extracted (Gerhardt
1984). After this discovery Plexaura has become a very valuable raw material
and a source of hard currency for developing countries (Venkataramanusjam
and Santhanam 1989). The reason for the accumulation of prostaglandins in
gorgonians became clear when it was found that the injection of negligible
amounts of this substance per os into fish caused the inevitable reaction
of vomiting. Fish avoided the food pellets which contained prostaglandin
(Gerhardt 1985), Thus, it serves as protection from predators. The same
function is accomplished in octocorals also by various terpenoids, which they
produce in significant amounts (Coli et al. 1977; Fenical and Harwell 1988).
Before terpenoids became known as metabolites of plants, on being discovered in octocorals they had been supposed to be products of their
symbiotic zooxanthellae. But recent studies have shown that they are
produced by the polyps themselves (Kokke et al. 1984; Coli et al. 1985).
The highest contents were found in colonies of the hermatypic gorgonians
Plexaura, Pseudoplexaura, Pseudopterogorgia, and Gorgonia. The
gorgonians Eunicea palmeri, E. succinea, Pseudoplexaura pororsa, and P.
flagellosa contain lactone-diterpenoids, such as crassine-acetate (Tursch et al.
1978). All the terpenoids are toxic and have a bad smell (Cieresko and
Karns-1973; Bakus 1981). Their content in both gorgonian octocorals and in
the aIcyonaceans appeared to be very high: 3-5% of the dry weight of the
colony (Coli et al. 1985). The presence of terpenoids made them toxic or
inedible. Extracts prepared from their colonies are toxic to fish and other
reef fauna. Experiments showed that over 50% of octocorals inhabiting the
GBR is toxic to reef fish. The most toxic of them were the common
aIcyonaceans Lemnalia and Sarcophyton (Coli et al. 1982). The terpenoids
of aIcyonaceans have antibacterial and antifungal properties (Bowden and
Coli 1983). In the experiments fish avoided the food pellets containing
extracts from their colonies or terpenoid preparations. Octocorals
permanently excrete terpenoid toxins into the water, thus inhibiting the
growth of their competitors - the scleractinian corals. Around them in calm
waters the concentration of terpenoids could attain 1-5 mg 1-1, which was
proved experimentally to be toxic for the corals Acropora and Porites. Their
inhibition by neighboring octocorals has been established (Bowden and Coli
1983; Sammarco et al. 1983; Coli et al. 1985).
The zoantharians contain their own toxins - palytoxins (Scheuer 1969;
Kimura et al. 1972). Therefore, they are practically left ungrazed by
predators, while some of their species do not have any exosceleton. They
also contain a significant amount of the biologically active substance
serotonine, a stimulator of propagation in animals (Cieresko and Karns
1973).
The above information shows that octocorals and zoantharians contain a
wide selection of biologically active compounds, and so they have become a
323
15%. Its content represents in colonies of Plexaura up to 5-8% of their dry
weight, which is 10 7 times more than in tissues of other animals, and by an
order more than in sheep testis, from which it is usually extracted (Gerhardt
1984). After this discovery Plexaura has become a very valuable raw material
and a source of hard currency for developing countries (Venkataramanusjam
and Santhanam 1989). The reason for the accumulation of prostaglandins in
gorgonians became clear when it was found that the injection of negligible
amounts of this substance per os into fish caused the inevitable reaction
of vomiting. Fish avoided the food pellets which contained prostaglandin
(Gerhardt 1985), Thus, it serves as protection from predators. The same
function is accomplished in octocorals also by various terpenoids, which they
produce in significant amounts (Coli et al. 1977; Fenical and Harwell 1988).
Before terpenoids became known as metabolites of plants, on being discovered in octocorals they had been supposed to be products of their
symbiotic zooxanthellae. But recent studies have shown that they are
produced by the polyps themselves (Kokke et al. 1984; Coli et al. 1985).
The highest contents were found in colonies of the hermatypic gorgonians
Plexaura, Pseudoplexaura, Pseudopterogorgia, and Gorgonia. The
gorgonians Eunicea palmeri, E. succinea, Pseudoplexaura pororsa, and P.
flagellosa contain lactone-diterpenoids, such as crassine-acetate (Tursch et al.
1978). All the terpenoids are toxic and have a bad smell (Cieresko and
Karns-1973; Bakus 1981). Their content in both gorgonian octocorals and in
the aIcyonaceans appeared to be very high: 3-5% of the dry weight of the
colony (Coli et al. 1985). The presence of terpenoids made them toxic or
inedible. Extracts prepared from their colonies are toxic to fish and other
reef fauna. Experiments showed that over 50% of octocorals inhabiting the
GBR is toxic to reef fish. The most toxic of them were the common
aIcyonaceans Lemnalia and Sarcophyton (Coli et al. 1982). The terpenoids
of aIcyonaceans have antibacterial and antifungal properties (Bowden and
Coli 1983). In the experiments fish avoided the food pellets containing
extracts from their colonies or terpenoid preparations. Octocorals
permanently excrete terpenoid toxins into the water, thus inhibiting the
growth of their competitors - the scleractinian corals. Around them in calm
waters the concentration of terpenoids could attain 1-5 mg 1-1, which was
proved experimentally to be toxic for the corals Acropora and Porites. Their
inhibition by neighboring octocorals has been established (Bowden and Coli
1983; Sammarco et al. 1983; Coli et al. 1985).
The zoantharians contain their own toxins - palytoxins (Scheuer 1969;
Kimura et al. 1972). Therefore, they are practically left ungrazed by
predators, while some of their species do not have any exosceleton. They
also contain a significant amount of the biologically active substance
serotonine, a stimulator of propagation in animals (Cieresko and Karns
1973).
The above information shows that octocorals and zoantharians contain a
wide selection of biologically active compounds, and so they have become a