406
Destruction and Recovery of Reef Systems, Reef and Man
water warming during the El Nino period many reef systems were also
inhibited by anthropogenic influence and by the Acanthaster plagues, which
could also weaken their endurance to temperature stress (Glynn 1984).
In the same El Nino period of 1982-1983 mass mortality of some fish, of
the urchins Diadema, and of the reef sea stars was also recorded on reefs of
the Caribbean basin and Florida (Dungan et al. 1982; Lessios et al. 1983).
The authors who described these phenomena supposed that they had been
caused by the joint impact of a number of factors and, above all ,by
anthropogenic stress and overheating. An enhanced excretion of mucus by
stressed and dying corals stimulates the development of bacteria, including
the pathogenic ones, which cause the death of animals, also enfeebled by
the stress caused by diseases. Corallovore fish and asteroids did not die
during the periods of mass mortality of corals, but grazed the remaining
ones, especially the young coral colonies (Glynn 1983). On the other hand,
the mass mortality of the urchins Diadema, which graze on macrophytes,
inhibits the recruitment of corals after their period of mortality (Lessios et
al. 1984). Therefore, the regeneration of coral communities, destryed by the
catastrophic events of bleaching and mass mortality, could be delayed and
on some reefs it could even be stopped, resulting then in their final
destruction (Glynn et al. 1988). The repetitions of these events on an even
larger scale, which happened again in the western Atlantic in 1987, proves
the contention, that we are witnessing the process of global destabilization
of coral-reef ecosystems, which endangers their very existence (Glynn 1984).
It happens because these mature and complex ecosystems, extremely
sensitive to any kinds of external influence, are functioning even in natural
conditions at their upper limits of endurance of physical stress. The corals,
which compose the core their group, in the summer period exist at
temperatares of only 2-3 °C below the lethal level. In zones of tropical
cyclones they are subjected to periodical cathastrophic damage within a
time-scale hardly permitting their complete recovery (i.e., 5-7 years). In
this situation, the addition of anthropogenic stress causes their chronic
global destabilization, which we are now witnessing (Bunkley-Williams and
Williams 1990).
11.3 Coral Diseases
The exposure of corals to diseases had been first discovered by Antnnius in
1973. Later he described four kinds of these (Antonius 1981, 1984, 1989).
Two of the diseases, "white bacteriosis" and the "pull-in of polyps" injure
corals only under stress conditions, such as overheating or pollution (Lewin
and Peters 1983; Antonius 1988; Chesher 1985; Kuhlmann 1988b; Edmunds
1991). Diseased corals pull in their polyps completely, abandoning activity.
Destruction and Recovery of Reef Systems, Reef and Man
water warming during the El Nino period many reef systems were also
inhibited by anthropogenic influence and by the Acanthaster plagues, which
could also weaken their endurance to temperature stress (Glynn 1984).
In the same El Nino period of 1982-1983 mass mortality of some fish, of
the urchins Diadema, and of the reef sea stars was also recorded on reefs of
the Caribbean basin and Florida (Dungan et al. 1982; Lessios et al. 1983).
The authors who described these phenomena supposed that they had been
caused by the joint impact of a number of factors and, above all ,by
anthropogenic stress and overheating. An enhanced excretion of mucus by
stressed and dying corals stimulates the development of bacteria, including
the pathogenic ones, which cause the death of animals, also enfeebled by
the stress caused by diseases. Corallovore fish and asteroids did not die
during the periods of mass mortality of corals, but grazed the remaining
ones, especially the young coral colonies (Glynn 1983). On the other hand,
the mass mortality of the urchins Diadema, which graze on macrophytes,
inhibits the recruitment of corals after their period of mortality (Lessios et
al. 1984). Therefore, the regeneration of coral communities, destryed by the
catastrophic events of bleaching and mass mortality, could be delayed and
on some reefs it could even be stopped, resulting then in their final
destruction (Glynn et al. 1988). The repetitions of these events on an even
larger scale, which happened again in the western Atlantic in 1987, proves
the contention, that we are witnessing the process of global destabilization
of coral-reef ecosystems, which endangers their very existence (Glynn 1984).
It happens because these mature and complex ecosystems, extremely
sensitive to any kinds of external influence, are functioning even in natural
conditions at their upper limits of endurance of physical stress. The corals,
which compose the core their group, in the summer period exist at
temperatares of only 2-3 °C below the lethal level. In zones of tropical
cyclones they are subjected to periodical cathastrophic damage within a
time-scale hardly permitting their complete recovery (i.e., 5-7 years). In
this situation, the addition of anthropogenic stress causes their chronic
global destabilization, which we are now witnessing (Bunkley-Williams and
Williams 1990).
11.3 Coral Diseases
The exposure of corals to diseases had been first discovered by Antnnius in
1973. Later he described four kinds of these (Antonius 1981, 1984, 1989).
Two of the diseases, "white bacteriosis" and the "pull-in of polyps" injure
corals only under stress conditions, such as overheating or pollution (Lewin
and Peters 1983; Antonius 1988; Chesher 1985; Kuhlmann 1988b; Edmunds
1991). Diseased corals pull in their polyps completely, abandoning activity.