278
Communities of Corals in Reef Ecosystems
In the central GBR the octocorals are also one of the main components
of sessile benthos, quite comparable by percentage of bottom cover and by
number of species to the scleractinian hard corals (Verseveldt 1977; Dinesen
1983). By parameters of composition and by structure the communities of
octocorals are similar here those described on reefs of the Red Sea and of
New Guinea. The alcyoniids, nephtheids and xeniids were dominating there
too. Some difference was noted by the appearance of new leading
alcyonacean genera like Lemnalia and Paralemnalia (fam. Nephtheidae),
Efflatounaria (fam. Xeniidae) and Asterospicularia (same name as family).
In the lagoonal part of the GBR the octocoral communities were dominated
by the leading alcyonacean species Sarcophyton tracheliphorum,
Lobophytum crassum, L. pauciflorum, Sinularia variabilis, S. flexibilis, S.
polydactila, Nephthea millis, Xenia sp., Heteroxenia sp., Clavularia sp.,
Alcyonium sp., and Cespicularia sp.
Our observations on octocorals distribution and on their taxonomic composition in the GBR region showed that their share in the formation of coral
communities is most remarkable in biotopes of lagoonal patch reefs, where
they survived destructive attacks of Acanthaster (Lizard Island), and in the
biotopes of flats and slopes at the fringing reefs around high islands, where
they had been subjected to terrigenous siltation (Paradise Island). In such
biotopes, octocorals are largely dominating in coral communities, covering
50-90% of areas of bottom inhabited by sessile fauna. On Lizard Islands
some reefs previously destroyed by Acanthaster were totally occupied by the
common alcyonaceans Alcyonium, Sarcophyton, Lobophytum, Sinularia,
and Xenia. Slopes and the base of reefs were inhabited by dense populations
of the gorgonian funcella tragilis. The symbiotic gorgonaceans, Plexauroides
and Isis were common also on slopes of the fringing reefs off Paradise
Island. Reefs of the Capricornia group escaped the Acanthaster plaques and
thus preserved stable coral commuhities for a long time. The octocorals
were their significant components only in the calm shallow biotopes of
slopes, of leeward reefs and shallow biotopes of reef flat and patch reefs.
They occupied in such biotopes 5 to 20% of area covered with corals. In
shallow biotopes the associations "Lemnalia-Paralemnalia-Cladiella-Xenia"
were most comon. At the reef-flat crevices Capnella, Asterospicularia and
Tubipora were humerous. On windward slopes within the thickets of ramose
corals Acropora large settlements of Sinularia hirta were recorded. The
gorgonaceans Rumpella and Isis were numerous on reef slopes of the
leeward side. At the foot of reefs, at depths of 18-22m among rocks and
rubble, Alcyonium, Sarcophyton, Pashyclavularia and the gorgonian funcella
occurred.
We have observed unusually abundant and diverse communities of octocorals on the monsoon reefs off the coast of central Vietnam. On some of
these reefs they formed large monospecific settlements which covered big
coral knolls and lots of reef-flat areas like a carpet. Most often these were
the species of Lobophytum or Sinularia. The fauna of octocorals here
Communities of Corals in Reef Ecosystems
In the central GBR the octocorals are also one of the main components
of sessile benthos, quite comparable by percentage of bottom cover and by
number of species to the scleractinian hard corals (Verseveldt 1977; Dinesen
1983). By parameters of composition and by structure the communities of
octocorals are similar here those described on reefs of the Red Sea and of
New Guinea. The alcyoniids, nephtheids and xeniids were dominating there
too. Some difference was noted by the appearance of new leading
alcyonacean genera like Lemnalia and Paralemnalia (fam. Nephtheidae),
Efflatounaria (fam. Xeniidae) and Asterospicularia (same name as family).
In the lagoonal part of the GBR the octocoral communities were dominated
by the leading alcyonacean species Sarcophyton tracheliphorum,
Lobophytum crassum, L. pauciflorum, Sinularia variabilis, S. flexibilis, S.
polydactila, Nephthea millis, Xenia sp., Heteroxenia sp., Clavularia sp.,
Alcyonium sp., and Cespicularia sp.
Our observations on octocorals distribution and on their taxonomic composition in the GBR region showed that their share in the formation of coral
communities is most remarkable in biotopes of lagoonal patch reefs, where
they survived destructive attacks of Acanthaster (Lizard Island), and in the
biotopes of flats and slopes at the fringing reefs around high islands, where
they had been subjected to terrigenous siltation (Paradise Island). In such
biotopes, octocorals are largely dominating in coral communities, covering
50-90% of areas of bottom inhabited by sessile fauna. On Lizard Islands
some reefs previously destroyed by Acanthaster were totally occupied by the
common alcyonaceans Alcyonium, Sarcophyton, Lobophytum, Sinularia,
and Xenia. Slopes and the base of reefs were inhabited by dense populations
of the gorgonian funcella tragilis. The symbiotic gorgonaceans, Plexauroides
and Isis were common also on slopes of the fringing reefs off Paradise
Island. Reefs of the Capricornia group escaped the Acanthaster plaques and
thus preserved stable coral commuhities for a long time. The octocorals
were their significant components only in the calm shallow biotopes of
slopes, of leeward reefs and shallow biotopes of reef flat and patch reefs.
They occupied in such biotopes 5 to 20% of area covered with corals. In
shallow biotopes the associations "Lemnalia-Paralemnalia-Cladiella-Xenia"
were most comon. At the reef-flat crevices Capnella, Asterospicularia and
Tubipora were humerous. On windward slopes within the thickets of ramose
corals Acropora large settlements of Sinularia hirta were recorded. The
gorgonaceans Rumpella and Isis were numerous on reef slopes of the
leeward side. At the foot of reefs, at depths of 18-22m among rocks and
rubble, Alcyonium, Sarcophyton, Pashyclavularia and the gorgonian funcella
occurred.
We have observed unusually abundant and diverse communities of octocorals on the monsoon reefs off the coast of central Vietnam. On some of
these reefs they formed large monospecific settlements which covered big
coral knolls and lots of reef-flat areas like a carpet. Most often these were
the species of Lobophytum or Sinularia. The fauna of octocorals here