276
Communities of Corals in Reef Ecosystems
colonize the destabilized or polluted reefs. We have observed this
phenomenon in Kaneohe Bay, Hawaii, where large areas of dead corals
killed by pollution were covered by carpets of the zoantharians Zoanthus
pacificus and Palythoa vestitus. They often inhabit also the patch reefs,
where there are plenty of dead coral heads. The most zone, which is usually
filled with dead corals and rubble, is colonized on many reefs by Zoanthus
sociatus.
All zoantharians possess zooxanthellae and also catch zooplankton (ct.
Sect. 9.22). The rate of their lateral growth is rather high - up to 1l.5 cm month- 1 (Karlson 1983). Thus, they could easily overgrow and force
out other competing sessile organisms. They multiply mostly vegatatively,
being also capable of sexual reproduction. Their mortality is high, caused by
surf action and grazing pressure. They are consumed by some urchins and
fish insensitive to their toxins (Cooke 1976). But the fast-growing
zoantharians may quickly repair the damage (Karlson, 1983). Some
zoantharians contain biologically active toxic substances of interest to
pharmacology (Moore and Scheuer 1971; Kimura et al. 1972). Fish, when
feeding on zoantharians, might also become toxic (Hashimoto et al. 1969).
The octocorals are a common component of coral-reef fauna, especially
on destabilized, damaged or monsoon reefs subjected to terrigenous
siltation, where the growth of scleractinian corals is inhibited. They grow
faster with standing well siltation and changes in salinity. Among such
habitats are many Caribbean reefs, reefs off Florida, off the Vietnamese
coast, and reefs around high islands in lagoons of the GBR. The octocorals
are often leading components of coral communities that are recovering after
attacks by Acanthaster or after hurricanes (Nishihira and Yamazato 1974;
Nishihira 1981; Yoshioka and Yoshioka 1989). They occupy mostly biotopes
with low or moderate turbulence, while the ahermatypic species prefer
shadowed niches or dark deep zones (Tursch and Tursch 1982). In these
sites they cover 20-50% of bottom areas occupied by coral communities.
On regenerating reefs it could be even more - over 90%. An important role
of octocorals in reef benthic communities then seems to be obvious.
Nevertheless, in descriptions of the structure of coral communities they have
been often ignored. In part, this was a consequence of their indefinite
situation in the taxonomic system and of the difficult procedure of their
identification. Therefore, most researchers include them in the taxonomic
lists of coral communities at the level of genera (Dinesen 1983).
In the Red Sea, among octocorals, the alcyonaceans largely dominate.
Although not very diverse in this basin, they still playa significant role in
the formation of reef bottom fauna (Finshelson 1973; Schuhmacher 1973;
Verseweldt 1974; Mergner and Svoboda 1977; Benayahu and Loya 1977).
On reefs of Eilat, where these studies have been mostly made, the most
abundant growth of alcyonacean octocorals was recorded in shallows of
submerged flats and on reef slopes. Their communities in shallows of reef
flats are formed mostly by the common alcyonaceans, Lithophyton,
Communities of Corals in Reef Ecosystems
colonize the destabilized or polluted reefs. We have observed this
phenomenon in Kaneohe Bay, Hawaii, where large areas of dead corals
killed by pollution were covered by carpets of the zoantharians Zoanthus
pacificus and Palythoa vestitus. They often inhabit also the patch reefs,
where there are plenty of dead coral heads. The most zone, which is usually
filled with dead corals and rubble, is colonized on many reefs by Zoanthus
sociatus.
All zoantharians possess zooxanthellae and also catch zooplankton (ct.
Sect. 9.22). The rate of their lateral growth is rather high - up to 1l.5 cm month- 1 (Karlson 1983). Thus, they could easily overgrow and force
out other competing sessile organisms. They multiply mostly vegatatively,
being also capable of sexual reproduction. Their mortality is high, caused by
surf action and grazing pressure. They are consumed by some urchins and
fish insensitive to their toxins (Cooke 1976). But the fast-growing
zoantharians may quickly repair the damage (Karlson, 1983). Some
zoantharians contain biologically active toxic substances of interest to
pharmacology (Moore and Scheuer 1971; Kimura et al. 1972). Fish, when
feeding on zoantharians, might also become toxic (Hashimoto et al. 1969).
The octocorals are a common component of coral-reef fauna, especially
on destabilized, damaged or monsoon reefs subjected to terrigenous
siltation, where the growth of scleractinian corals is inhibited. They grow
faster with standing well siltation and changes in salinity. Among such
habitats are many Caribbean reefs, reefs off Florida, off the Vietnamese
coast, and reefs around high islands in lagoons of the GBR. The octocorals
are often leading components of coral communities that are recovering after
attacks by Acanthaster or after hurricanes (Nishihira and Yamazato 1974;
Nishihira 1981; Yoshioka and Yoshioka 1989). They occupy mostly biotopes
with low or moderate turbulence, while the ahermatypic species prefer
shadowed niches or dark deep zones (Tursch and Tursch 1982). In these
sites they cover 20-50% of bottom areas occupied by coral communities.
On regenerating reefs it could be even more - over 90%. An important role
of octocorals in reef benthic communities then seems to be obvious.
Nevertheless, in descriptions of the structure of coral communities they have
been often ignored. In part, this was a consequence of their indefinite
situation in the taxonomic system and of the difficult procedure of their
identification. Therefore, most researchers include them in the taxonomic
lists of coral communities at the level of genera (Dinesen 1983).
In the Red Sea, among octocorals, the alcyonaceans largely dominate.
Although not very diverse in this basin, they still playa significant role in
the formation of reef bottom fauna (Finshelson 1973; Schuhmacher 1973;
Verseweldt 1974; Mergner and Svoboda 1977; Benayahu and Loya 1977).
On reefs of Eilat, where these studies have been mostly made, the most
abundant growth of alcyonacean octocorals was recorded in shallows of
submerged flats and on reef slopes. Their communities in shallows of reef
flats are formed mostly by the common alcyonaceans, Lithophyton,