Reproduction of Corals
287
In most viviparous and in spawning corals, in their polyps and in their
whole population on separate reefs, gametogenesis cycles are synchronized
(Richmond and Jokiel 1984; Stoddart and Black 1985; Kojis 1986). The
number of these cycles in corals with monthly periods of multiplication
(coming forth of planulae) is two to three per year, and in corals with annual
cycles of multiplication one (Stimson 1978; Kojis 1986). In the last case, the
oocytes appear in the tissues of polyps in the spring and become mature in
autumn. The mature oocytes are reddish. In some species they contain the
algal symbionts, zooxanthellae (Babcock et al. 1986). Their number in
gonads of one small-to-average polyp varies between 10 and 120 (Stimson
1978). In polyps of large corals, like the solitary coral Fungia, the number of
oocytes in gonads might reach up to several millions. Their size varies
between 20-600~.
In polyps of the viviparous hermaphroditic corals Pocillopora damicornis
and Acropora formosa the ovaries and the spermaries are formed in tissues
of the mesentery within the same polyp (Stoddart and Black 1985). The
number of oocytes in one polyp of Pocillopora was 18-24, and in one polyp
of Acropora close to 100. The oocytes are self-fertilized inside the polyp. In
Pocillopora some oocytes are parthenogenetic. The ova develop to the
phase of planulae, which then remain to mature inside the mesentery,
attached to its walls by special stalks (Kojis 1986). In bisexual viviparous
corals, like Fungia, Dendrophyllia, and Tubastrea, the oocytes are fertilized
inside the mesentery by spermatozoids which swim into the mesentarial
cavity of the polyp through its mouth.
The spawning hermaphrodite corals, which dominate in reef coral
communities, employ two types of fertilization: the obligate crossfertilization or mixed fertilization, when a part of the oocytes are fertilized
by spermatozoids from the same polyp or from other polyps of the same
colony genetically equivalent to the former. An example of obligate crossfertilization is given by the coral Montipora digitate. The oocytes of this
coral "recognize" their own spermatozoids and reject them (Heyward and
Babcock 1986). Inbreeding (external fertilization by spermatozoids from the
same colony) is largely widespread among the spawning species, but it is not
clearcut, because a part of their oocytes is fertilized by sperm from
synchronously spawning colonies. Moreover, most spawning hermaphrodite
corals have mechanisms restricting the possibility of inbreeding. In some of
them the final fissions occur in the oocytes 15-20 min after they have been
spawned into the water. Thus, they cannot be self-fertilized inside the polyp.
In the coral Goniastrea aspera, the oocytes thrown out by polyps settle down
to the bottom and become glued onto the substrate. Here they are fertilized
by sperm excreted by neighboring colonies (Heyward and Babcock 1986).
But in most hermaphrodite spawning corals special lumps of ca. 1 mm size
are formed in the mesenteries of their polyps, which hold together the
oocytes and the unmatured sperm. The oocytes in these lumps contain much
fat. On being thrown out, these lumps float up and soon desintegrate in the
287
In most viviparous and in spawning corals, in their polyps and in their
whole population on separate reefs, gametogenesis cycles are synchronized
(Richmond and Jokiel 1984; Stoddart and Black 1985; Kojis 1986). The
number of these cycles in corals with monthly periods of multiplication
(coming forth of planulae) is two to three per year, and in corals with annual
cycles of multiplication one (Stimson 1978; Kojis 1986). In the last case, the
oocytes appear in the tissues of polyps in the spring and become mature in
autumn. The mature oocytes are reddish. In some species they contain the
algal symbionts, zooxanthellae (Babcock et al. 1986). Their number in
gonads of one small-to-average polyp varies between 10 and 120 (Stimson
1978). In polyps of large corals, like the solitary coral Fungia, the number of
oocytes in gonads might reach up to several millions. Their size varies
between 20-600~.
In polyps of the viviparous hermaphroditic corals Pocillopora damicornis
and Acropora formosa the ovaries and the spermaries are formed in tissues
of the mesentery within the same polyp (Stoddart and Black 1985). The
number of oocytes in one polyp of Pocillopora was 18-24, and in one polyp
of Acropora close to 100. The oocytes are self-fertilized inside the polyp. In
Pocillopora some oocytes are parthenogenetic. The ova develop to the
phase of planulae, which then remain to mature inside the mesentery,
attached to its walls by special stalks (Kojis 1986). In bisexual viviparous
corals, like Fungia, Dendrophyllia, and Tubastrea, the oocytes are fertilized
inside the mesentery by spermatozoids which swim into the mesentarial
cavity of the polyp through its mouth.
The spawning hermaphrodite corals, which dominate in reef coral
communities, employ two types of fertilization: the obligate crossfertilization or mixed fertilization, when a part of the oocytes are fertilized
by spermatozoids from the same polyp or from other polyps of the same
colony genetically equivalent to the former. An example of obligate crossfertilization is given by the coral Montipora digitate. The oocytes of this
coral "recognize" their own spermatozoids and reject them (Heyward and
Babcock 1986). Inbreeding (external fertilization by spermatozoids from the
same colony) is largely widespread among the spawning species, but it is not
clearcut, because a part of their oocytes is fertilized by sperm from
synchronously spawning colonies. Moreover, most spawning hermaphrodite
corals have mechanisms restricting the possibility of inbreeding. In some of
them the final fissions occur in the oocytes 15-20 min after they have been
spawned into the water. Thus, they cannot be self-fertilized inside the polyp.
In the coral Goniastrea aspera, the oocytes thrown out by polyps settle down
to the bottom and become glued onto the substrate. Here they are fertilized
by sperm excreted by neighboring colonies (Heyward and Babcock 1986).
But in most hermaphrodite spawning corals special lumps of ca. 1 mm size
are formed in the mesenteries of their polyps, which hold together the
oocytes and the unmatured sperm. The oocytes in these lumps contain much
fat. On being thrown out, these lumps float up and soon desintegrate in the