288
Communities of Corals in Reef Ecosystems
surface film. Then during several tens of minutes the sperm matures and the
fertilization proceeds. However, this is mostly cross-fertilization. Because of
the synchronized spawning of all coral populations at the sea surface, a mass
of eggs and sperm accumulates in the surface film itself (Harrison et al.
1984; Babcock et al. 1986). The accumulation of sexual products of corals
during their synchronous spawning results even in the formation of rosy
slicks on the sea surface. The spawning proceeds synchronously in all polyps
of the colony. Polyps of the corals Acropora or Platygyra slowly let out the
lumps of gametes within 10-50 min. Other species throw out clouds of
sperm and lumps of oocytes by instant contraction of all polyps of the colony
(Goniastrea, Fungia).
The process of gametogenesis and spawning are synchronized in the
polyps of corals not only within one colony, but also in all colonies of the
population on a given reef. In viviparous corals the synchronization of
the monthly periods of hatching of their larvae is clearly connected with and
triggered by the phases of the moon. In spawning corals with annual cycles,
the connection between the time of synchronous breeding and both the
phases of the moon and the temperature of the water has been established
(Rinkevich and Loya 1979a; Harriott 1983; Fadallah 1983; Jokiel 1984,
1985; Jokie! 1985). Moreover, on the Pacific reefs the times of breeding in
spawning corals are synchronized also in most members of the coral
community, be it scleractinians or octocorals. On reefs of the GBR the time
of mass spawning of corals within a week of the breeding period was
established to be simultaneous for over 130 species - representatives of 12
families of corals out of 15 inhabiting the central part of the GBR (Willis et
al. 1985; Babcock et al. 1986). The mass spawning is triggered in most
species when the water temperature reaches 26°C on the first day after full
moon, which happens in this region in late October. The process of
maturation of gametes is controlled by the water temperature, while the
moon phase (actually the level of illumination at night) controls the exact
time of spawning. The latter was proved in experiments by imitating
moonlight (Richmond and Jokiel 1984). On reefs of different regions the
times of mass breeding of corals appear to be different, being triggered at
various levels of water temperature and by different phases of the moon for
the same coral species (Loya 1972). Some corals of the GBR with a cycle of
spawning of two times annually - at the end of October and at the end of
November - spawn exactly at the same moon phases (Acropora latisetella,
Hydnophora exaesa). Maximum rates of spawning during synchronous
breeding were observed during the first half of the night, from sunset till
midnight.
The synchronous spawning of tens of different species of corals is in itself
an outstanding biological phenomenon (Harrison et al. 1984). But it seem to
be happening only in very diverse and abundant coral communities of the
GBR. This phenomenon has also been observed in the region of Fiji Island.
But on Caribbean and Red Sea reefs this kind of synchronous breeding
Communities of Corals in Reef Ecosystems
surface film. Then during several tens of minutes the sperm matures and the
fertilization proceeds. However, this is mostly cross-fertilization. Because of
the synchronized spawning of all coral populations at the sea surface, a mass
of eggs and sperm accumulates in the surface film itself (Harrison et al.
1984; Babcock et al. 1986). The accumulation of sexual products of corals
during their synchronous spawning results even in the formation of rosy
slicks on the sea surface. The spawning proceeds synchronously in all polyps
of the colony. Polyps of the corals Acropora or Platygyra slowly let out the
lumps of gametes within 10-50 min. Other species throw out clouds of
sperm and lumps of oocytes by instant contraction of all polyps of the colony
(Goniastrea, Fungia).
The process of gametogenesis and spawning are synchronized in the
polyps of corals not only within one colony, but also in all colonies of the
population on a given reef. In viviparous corals the synchronization of
the monthly periods of hatching of their larvae is clearly connected with and
triggered by the phases of the moon. In spawning corals with annual cycles,
the connection between the time of synchronous breeding and both the
phases of the moon and the temperature of the water has been established
(Rinkevich and Loya 1979a; Harriott 1983; Fadallah 1983; Jokiel 1984,
1985; Jokie! 1985). Moreover, on the Pacific reefs the times of breeding in
spawning corals are synchronized also in most members of the coral
community, be it scleractinians or octocorals. On reefs of the GBR the time
of mass spawning of corals within a week of the breeding period was
established to be simultaneous for over 130 species - representatives of 12
families of corals out of 15 inhabiting the central part of the GBR (Willis et
al. 1985; Babcock et al. 1986). The mass spawning is triggered in most
species when the water temperature reaches 26°C on the first day after full
moon, which happens in this region in late October. The process of
maturation of gametes is controlled by the water temperature, while the
moon phase (actually the level of illumination at night) controls the exact
time of spawning. The latter was proved in experiments by imitating
moonlight (Richmond and Jokiel 1984). On reefs of different regions the
times of mass breeding of corals appear to be different, being triggered at
various levels of water temperature and by different phases of the moon for
the same coral species (Loya 1972). Some corals of the GBR with a cycle of
spawning of two times annually - at the end of October and at the end of
November - spawn exactly at the same moon phases (Acropora latisetella,
Hydnophora exaesa). Maximum rates of spawning during synchronous
breeding were observed during the first half of the night, from sunset till
midnight.
The synchronous spawning of tens of different species of corals is in itself
an outstanding biological phenomenon (Harrison et al. 1984). But it seem to
be happening only in very diverse and abundant coral communities of the
GBR. This phenomenon has also been observed in the region of Fiji Island.
But on Caribbean and Red Sea reefs this kind of synchronous breeding