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Communities of Corals in Reef Ecosystems
All of the long-living massive or columnar conservative corals (kstrategists) have annual cycles of breeding. Most of them are spawning, and
only a few of their species are viviparous. They reach maturity late and are
very prolific. Their planulae live long in the water column before settling
(Harriott 1982; Jokiel 1984; Szamant 1986). The spawning procedure
provides them a better possibility for cross-fertilization and so for the
production of heterozygote offspring, which are more viable and versatile,
and better adaptive to strange biotopes when settling. The synchronous
spawning of tens of their species also provides conditions for intergeneric
fertilization, thus promoting the appearance of new morphs and new species
in this group of corals - k-strategists. An important biological reason for
mass synchronous spawning in coral communities (and also in the
populations of viviparous species) could also be seen in the decreasing
mortality of eggs and planulae from grazing by fish and other planktonic and
benthic predators (Harrison 1985; Westheat and Reising 1988). The
predators cannot physically graze them out significantly during the short
period of their massive accumulation in the water column.
In octocorals and in zoantharians sexual breeding appears to be just as
important as in scleractinians, while they reproduce successfully also
asexually (Yamazato et ai. 1981; Fadallah et ai. 1984). Among zoantharians,
such spawning species are most numerous, which have external fertilization
(Cooke 1976; Karlson 1981). In populations of the mass species Zoanthus
sociatus and Palythoa caribbaereum there are colonies present
simultaneously with only hermaphroditic polyps, colonies with polyps of
both sexes, and also colonies with only monosexual polyps. Most octocorals
are bisexual, either spawning or viviparous, though hermaphroditic and
even the parthenogenetic species could also be found among them
(Weinberg and Weinberg 1979; Yamazato et ai. 1981; Benayahu and Loya
1984). Their vIviparous species are represented by Xenia, and
Parerythropodium, by some species of Alcyonium, by Anthelia, Eunicella,
and Muricea (Theodor 1967; Grigg 1977; Benayahu 1989). The alcyonacean
Capnella, which has bisexual colonies, takes special "care" of its offspring.
The eggs excreted by polyps instantly attach to the surface of the colony.
Here they are fertilized by sperm produced by polyps of a neighboring male
colony. The hatched planulae drop down to the bottom and start new
colonies near the mother ones, forming so a large monospecific settlement
of this octocoral, which could be up to several tens of square meters large
(Farrant 1985).
The spawning octocorals produce eggs, which are fertilized externally.
Among them are the common alcyonaceans Lobophytum, Sarcophyton, and
Sinularia, and most species of the genus Alsyonium (Yamazato et ai. 1981;
Babcock et ai. 1986). They, have bisexual colonies. The ovogenesis takes in
Lobophytum crassum 2 years, and the spermatogenesis 2 years. Spawning
occurs once a year. The number of oocytes in one polyp is 70-100, with a
diameter of 0.5 mm.
Communities of Corals in Reef Ecosystems
All of the long-living massive or columnar conservative corals (kstrategists) have annual cycles of breeding. Most of them are spawning, and
only a few of their species are viviparous. They reach maturity late and are
very prolific. Their planulae live long in the water column before settling
(Harriott 1982; Jokiel 1984; Szamant 1986). The spawning procedure
provides them a better possibility for cross-fertilization and so for the
production of heterozygote offspring, which are more viable and versatile,
and better adaptive to strange biotopes when settling. The synchronous
spawning of tens of their species also provides conditions for intergeneric
fertilization, thus promoting the appearance of new morphs and new species
in this group of corals - k-strategists. An important biological reason for
mass synchronous spawning in coral communities (and also in the
populations of viviparous species) could also be seen in the decreasing
mortality of eggs and planulae from grazing by fish and other planktonic and
benthic predators (Harrison 1985; Westheat and Reising 1988). The
predators cannot physically graze them out significantly during the short
period of their massive accumulation in the water column.
In octocorals and in zoantharians sexual breeding appears to be just as
important as in scleractinians, while they reproduce successfully also
asexually (Yamazato et ai. 1981; Fadallah et ai. 1984). Among zoantharians,
such spawning species are most numerous, which have external fertilization
(Cooke 1976; Karlson 1981). In populations of the mass species Zoanthus
sociatus and Palythoa caribbaereum there are colonies present
simultaneously with only hermaphroditic polyps, colonies with polyps of
both sexes, and also colonies with only monosexual polyps. Most octocorals
are bisexual, either spawning or viviparous, though hermaphroditic and
even the parthenogenetic species could also be found among them
(Weinberg and Weinberg 1979; Yamazato et ai. 1981; Benayahu and Loya
1984). Their vIviparous species are represented by Xenia, and
Parerythropodium, by some species of Alcyonium, by Anthelia, Eunicella,
and Muricea (Theodor 1967; Grigg 1977; Benayahu 1989). The alcyonacean
Capnella, which has bisexual colonies, takes special "care" of its offspring.
The eggs excreted by polyps instantly attach to the surface of the colony.
Here they are fertilized by sperm produced by polyps of a neighboring male
colony. The hatched planulae drop down to the bottom and start new
colonies near the mother ones, forming so a large monospecific settlement
of this octocoral, which could be up to several tens of square meters large
(Farrant 1985).
The spawning octocorals produce eggs, which are fertilized externally.
Among them are the common alcyonaceans Lobophytum, Sarcophyton, and
Sinularia, and most species of the genus Alsyonium (Yamazato et ai. 1981;
Babcock et ai. 1986). They, have bisexual colonies. The ovogenesis takes in
Lobophytum crassum 2 years, and the spermatogenesis 2 years. Spawning
occurs once a year. The number of oocytes in one polyp is 70-100, with a
diameter of 0.5 mm.