Anthropogenic Impacts
407
After several days their tissues fall out from colonies in stripes and they die.
Two other kinds of coral ills, the "white band" and the "black band"
disease (WBD and BBD) could be found also on otherwise quite healthy
reefs. Nevertheless, BBD might be stimulated by stress conditions
(Antonius 1981, 1984, 1989). Outbreakes of these diseases were recorded on
reefs where corals had been destroyed by cyclones, and then bored by
sponges and clams. On the destabilized reefs of Jamaica and Curacao, WBD
in-fected about 80% of corals (Rogers 1985; Peters 1988). Experiments
showed that young colonies of corals, regenerated from fragments of
branches, are most susceptive to diseases, and a significant part of them dies
(Bak and Criens 1981).
BBD is caused by the blue-green filamentous alga Phormidium corallicum
(Riitzler and Santavy 1983). This pathogenic alga induces a diseases similar
to BBD also in the gorgonian octocoral Pseudopterogorgia (Feingold 1988).
The transfer of pieces of diseased coral to healthy ones can infect them. The
infection agent of WBD is still unknown, but it is supposed to be a
bacterium (Peters et al. 1983). It is inhibited by antibiotics, though this
conclusion was put in doubt by Antonius (1984). Corals could become
diseased by WBD without any external stress influence. It damages mostly
the ramose corals acroporids and pocilloporids. The diseased corals mostly
die. The disease usually starts at the base of a colony and then in the form of
a white stripe extends upwards across the colony. Polyps in the damaged
zone die and the tissues are eaten by microfauna (Gladfelter 1982). On this
stripe often also BBD develops later on. This disease injures mostly massive
corals, as faviids and Platygyra. According to Chesher (1985), acroporid
corals at Tonga have been insured by the disease, induced by a blue-·green
filamentous algae resembling Oscillatoria.
Coral diseases are now under intensive investigation. It became evident
also that they strike mostly corals enfeebled by stress, in particular by the
activity of man of reefs (Segel and Ducklow 1982). Under the influence of
siltation and pollution in zones of such an activity the corals increase their
excretion of mucus, the excess of which stimulates the development of
bacteria, which then infect the corals themselves (Mitchell and Chet 1975;
Garrett and Ducklow 1975).
11.4 Anthropogenic Impacts
As mentioned above, reef ecosystems exist at their boundary of endurance
of physical stress. But its periodic character has allowed them not only to
survive, but also to flourish (Highsmith et al. 1980). Anthropogenic stress is
much more dangerous for them because in most cases it is not only
permanent but has also the tendency to increase with time (Kinsey 1988). In
407
After several days their tissues fall out from colonies in stripes and they die.
Two other kinds of coral ills, the "white band" and the "black band"
disease (WBD and BBD) could be found also on otherwise quite healthy
reefs. Nevertheless, BBD might be stimulated by stress conditions
(Antonius 1981, 1984, 1989). Outbreakes of these diseases were recorded on
reefs where corals had been destroyed by cyclones, and then bored by
sponges and clams. On the destabilized reefs of Jamaica and Curacao, WBD
in-fected about 80% of corals (Rogers 1985; Peters 1988). Experiments
showed that young colonies of corals, regenerated from fragments of
branches, are most susceptive to diseases, and a significant part of them dies
(Bak and Criens 1981).
BBD is caused by the blue-green filamentous alga Phormidium corallicum
(Riitzler and Santavy 1983). This pathogenic alga induces a diseases similar
to BBD also in the gorgonian octocoral Pseudopterogorgia (Feingold 1988).
The transfer of pieces of diseased coral to healthy ones can infect them. The
infection agent of WBD is still unknown, but it is supposed to be a
bacterium (Peters et al. 1983). It is inhibited by antibiotics, though this
conclusion was put in doubt by Antonius (1984). Corals could become
diseased by WBD without any external stress influence. It damages mostly
the ramose corals acroporids and pocilloporids. The diseased corals mostly
die. The disease usually starts at the base of a colony and then in the form of
a white stripe extends upwards across the colony. Polyps in the damaged
zone die and the tissues are eaten by microfauna (Gladfelter 1982). On this
stripe often also BBD develops later on. This disease injures mostly massive
corals, as faviids and Platygyra. According to Chesher (1985), acroporid
corals at Tonga have been insured by the disease, induced by a blue-·green
filamentous algae resembling Oscillatoria.
Coral diseases are now under intensive investigation. It became evident
also that they strike mostly corals enfeebled by stress, in particular by the
activity of man of reefs (Segel and Ducklow 1982). Under the influence of
siltation and pollution in zones of such an activity the corals increase their
excretion of mucus, the excess of which stimulates the development of
bacteria, which then infect the corals themselves (Mitchell and Chet 1975;
Garrett and Ducklow 1975).
11.4 Anthropogenic Impacts
As mentioned above, reef ecosystems exist at their boundary of endurance
of physical stress. But its periodic character has allowed them not only to
survive, but also to flourish (Highsmith et al. 1980). Anthropogenic stress is
much more dangerous for them because in most cases it is not only
permanent but has also the tendency to increase with time (Kinsey 1988). In