292
Communities of Corals in Reef Ecosystems
column or crawl on the bottom until they find a proper place and can settle.
The planulae of the viviparous species settle usually within 3-5 days, and
planulae of spawning corals within 2-3 weeks (Babcock 1984; Harrison et
al. 1984; Richmond and Jokiel 1984). But some of them may remain in the
water column even for several months, being drived by currents tens and
hundreds of kilometers away from the place of their hatching (Grigg 1981b;
Babcock 1988). Another mode of the spatial distribution of corals is the
settling of planulae on floating objects: on driftwood, coconuts, bottoms of
ships, on floating pumice, thus traveling thousands of kilometers (Roy and
Smith 1971; Jokiel 1984).
The rate of recruitment of corals was studied by placing in different reef
biotopes of some artificial substrate, like concrete plates or tubes, glass
plates or lime plates made by cutting, colonies of massive corals. On reefs of
the GBR the rates of recruitment was estimated to be within ten colonies
m- 2 year- 1 (Connell 1973; Bothwell 1983a). On the Atlantic reefs it was
less: three to four colonies (Rogers et al. 1984; Szamant-Froelich 1985). On
reefs of the Red Sea it was about five colonies m -2 year-I, the common
coral Stylophora pistillata dominating among the recruits (Loya 1976b). The
rate of recruitment was as a rule higher in communities where the conditions
of illumination and the content of nutrients were far from optimal: in poorly
illuminated, deep zones of reef slopes or zones situated in reefs surrounded
by waters impoverished in nutrients (Birkeland 1977). In reef zones with
optimal conditions the recruitment was inhibited by the macrophytes and
algal turfs flourishing there. The highest rates of recruitment showed the
most common ramose corals. On reef flats of Heren Island (GBR) these
were Acropora digitifera, A. millepora, A. cuneata, and Pocillopora
damicornis, which were thus contributing to the high density of their specific
population in the biotope (Connell 1973). The strategy of recruitment seems
to be different in viviparous and in spawning corals (Bothwell 1983a, 1984).
In the viviparous species Acropora cuneata and Pocillopora damicornis
recruitment proceeded mostly by the settling of their planulae, while in the
spawning species A. digitifera, A. millepora, and A. pulchra most of new
recruits descended from the rooted pieces of their branch, i.e., by vegetative
propagation. This strategy provides spawning species the possibility of
colonizing nearby areas of their native biotope, because their eggs and
larvae exist for a long time in the surface film and are driven far from the
area where they were produced (TunnicJiffe 1981; Highsmith 1982). It was
detected also that planulae of some species preferred to settle together in
one spot, which probably might increase the chances of their survival
(Goreau et al. 1981). Sometimes aggregations of recruited larvae were
formed by planulae of different species of the same genus of coral.
Corals spend for sexual breeding a significant portion of energy,
especially the viviparous ones, while the survival rate of their egg larvae and
spat is very low (Harrigan 1972; Goreau et al. 1981; Sammarco 1983). The
larvae and eggs are eaten by various planktonovores (Connell 1973).
Communities of Corals in Reef Ecosystems
column or crawl on the bottom until they find a proper place and can settle.
The planulae of the viviparous species settle usually within 3-5 days, and
planulae of spawning corals within 2-3 weeks (Babcock 1984; Harrison et
al. 1984; Richmond and Jokiel 1984). But some of them may remain in the
water column even for several months, being drived by currents tens and
hundreds of kilometers away from the place of their hatching (Grigg 1981b;
Babcock 1988). Another mode of the spatial distribution of corals is the
settling of planulae on floating objects: on driftwood, coconuts, bottoms of
ships, on floating pumice, thus traveling thousands of kilometers (Roy and
Smith 1971; Jokiel 1984).
The rate of recruitment of corals was studied by placing in different reef
biotopes of some artificial substrate, like concrete plates or tubes, glass
plates or lime plates made by cutting, colonies of massive corals. On reefs of
the GBR the rates of recruitment was estimated to be within ten colonies
m- 2 year- 1 (Connell 1973; Bothwell 1983a). On the Atlantic reefs it was
less: three to four colonies (Rogers et al. 1984; Szamant-Froelich 1985). On
reefs of the Red Sea it was about five colonies m -2 year-I, the common
coral Stylophora pistillata dominating among the recruits (Loya 1976b). The
rate of recruitment was as a rule higher in communities where the conditions
of illumination and the content of nutrients were far from optimal: in poorly
illuminated, deep zones of reef slopes or zones situated in reefs surrounded
by waters impoverished in nutrients (Birkeland 1977). In reef zones with
optimal conditions the recruitment was inhibited by the macrophytes and
algal turfs flourishing there. The highest rates of recruitment showed the
most common ramose corals. On reef flats of Heren Island (GBR) these
were Acropora digitifera, A. millepora, A. cuneata, and Pocillopora
damicornis, which were thus contributing to the high density of their specific
population in the biotope (Connell 1973). The strategy of recruitment seems
to be different in viviparous and in spawning corals (Bothwell 1983a, 1984).
In the viviparous species Acropora cuneata and Pocillopora damicornis
recruitment proceeded mostly by the settling of their planulae, while in the
spawning species A. digitifera, A. millepora, and A. pulchra most of new
recruits descended from the rooted pieces of their branch, i.e., by vegetative
propagation. This strategy provides spawning species the possibility of
colonizing nearby areas of their native biotope, because their eggs and
larvae exist for a long time in the surface film and are driven far from the
area where they were produced (TunnicJiffe 1981; Highsmith 1982). It was
detected also that planulae of some species preferred to settle together in
one spot, which probably might increase the chances of their survival
(Goreau et al. 1981). Sometimes aggregations of recruited larvae were
formed by planulae of different species of the same genus of coral.
Corals spend for sexual breeding a significant portion of energy,
especially the viviparous ones, while the survival rate of their egg larvae and
spat is very low (Harrigan 1972; Goreau et al. 1981; Sammarco 1983). The
larvae and eggs are eaten by various planktonovores (Connell 1973).