Communities Structure of Reef Corals
265
N,%
.7"0
7.7"
700
mo~----------~----------~
7tl L -________________________ ~
Fig. 7.6. Dependence of total number of coral species (N) upon light intensity (PARS)
on slopes of reef off Tohthu I., Vietnam. (Data by Titlyanov et a\. 1988c)
/I'
A
!J
Fig. 7.7. Model of successional changes in the index of species diversity in a coral
community: A with undisturbed gradual development, and B with development
periodically interrupted by moderate (I) and destructive (d) stress impacts
stochastic physical and biological impacts, such as hurricanes, extremely low
ebbs, long exposures, floods of cold or fresh waters accompanied by massive
siltations, Acanthaster plaques, epidemic diseases of corals, etc. (Dayton
and Hessler 1972; Goreau et al. 1972; Loya 1976c; Connell 1983; Bothwell
1984). These disturbances result in unselective deaths of corals and thus
make space for resruitments of new species (Colgan 1981). This hypothesis
is illustrated by the scheme of Fig. 7.7. The curve A predicts the changes of
species diversity in the coral community when the above-mentioned
disturbances are absent. In accordance with this theoretical prediction, at
the late phase of normal succession the species diversity as well as the total
number of species decrease. The curve B hypothetically describes the
possible changes of species diversity during the succession of a community