400
Destruction and Recovery of Reef Systems, Reef and Man
might also come about by a transfer of a mass of star's larvae from places of
invasion to healthy reefs by currents.
This ecological hypothesis offered by Kuhlmann (1971) seems to this
author to fit best the observed facts. The assumption of possible repetitions
of invasions within a short time, especially in regions permanently stressed
by man, which had been made on the basis of this hypothesis, was later
proved. The subsequent invasions which occurred in the GBR zone in
1979-1983 prove the point that the Acanthaster outbreaks are a unique
ecocatastrophe caused by an external cause (i.e., by man), rather than the
consequence of natural periodic fluctuations in the star's numbers, which
also occurred in the past. The opinions of the proponents of this latter
aspect are divergent in their explanations of the cause of outbreaks. One of
them sees it in their ability to migrate long distances and to form breeding
aggregations. They suppose that the stars, thus accumulated in one place,
graze out corals, which in turn also graze the star's larvae and eggs. As a
result, the number of surviving star's larvae should increase, thus furthering
their successful breeding. Repetitions of such cycles could gradually lead to
an increase in the total density of their populations (Ormond and Campbell
1973, 1974). Other authors see as starting place for the outbreaks the reefs,
damaged by cyclones (Dana et al. 1972). The cyclones, smashing all corals
onto the shallows, force the stars to migrate down to the deeper zones of the
slope for feeding, where corals remain safe. In this way they might form
aggregations, which could form the start of the "army of invasion".
Birkeland (1982) thinks that good nutrients conditions for phytoplankton,
created by periodic rains near high islands, might improve the possibility of
survival of the star's larvae. This could lead to an increase in the star's
numbers. Vine (1970) also see the cause of outbreaks as a natural periodic
phenomenon in the fluctuation of conditions for survival of the star's larvae.
We may agree that all the above phenomena could cause the periodic
fluctuations in the predator's population density, but only on condition that
the pressure of grazers is lacking. But the main objection is that if these
fluctuations are natural they ought to have been recorded before at some
reefs, which actually is not the case. Many facts cannot be explained either
by Kuhlmann's hypothesis. For example, why did some reefs situated amid
areas of the most severe star outbreaks remain safe? Moreover, in such
uninfested zones some reefs heavily exploited by man also remained.
Therefore, the problem of Acanthaster plagues is still one of the most
intriguing and urgent in reef ecology.
As for the measures in the fight against the infestations, stars were
collected by scuba divers. Off eastern Samoa and Okinawa divers collected
hundred thousands of them. There were attempts to stop the moving front
of stars by electrified wire - an electric barrier. A method was also
developed for killing them by injection of copper-sulfate solution by divers
(Chesher 1969; Sale et al. 1976). But all these measures appeared to be only
palliative and extremely expensive. To kill one star on the reef cos ted 35
Destruction and Recovery of Reef Systems, Reef and Man
might also come about by a transfer of a mass of star's larvae from places of
invasion to healthy reefs by currents.
This ecological hypothesis offered by Kuhlmann (1971) seems to this
author to fit best the observed facts. The assumption of possible repetitions
of invasions within a short time, especially in regions permanently stressed
by man, which had been made on the basis of this hypothesis, was later
proved. The subsequent invasions which occurred in the GBR zone in
1979-1983 prove the point that the Acanthaster outbreaks are a unique
ecocatastrophe caused by an external cause (i.e., by man), rather than the
consequence of natural periodic fluctuations in the star's numbers, which
also occurred in the past. The opinions of the proponents of this latter
aspect are divergent in their explanations of the cause of outbreaks. One of
them sees it in their ability to migrate long distances and to form breeding
aggregations. They suppose that the stars, thus accumulated in one place,
graze out corals, which in turn also graze the star's larvae and eggs. As a
result, the number of surviving star's larvae should increase, thus furthering
their successful breeding. Repetitions of such cycles could gradually lead to
an increase in the total density of their populations (Ormond and Campbell
1973, 1974). Other authors see as starting place for the outbreaks the reefs,
damaged by cyclones (Dana et al. 1972). The cyclones, smashing all corals
onto the shallows, force the stars to migrate down to the deeper zones of the
slope for feeding, where corals remain safe. In this way they might form
aggregations, which could form the start of the "army of invasion".
Birkeland (1982) thinks that good nutrients conditions for phytoplankton,
created by periodic rains near high islands, might improve the possibility of
survival of the star's larvae. This could lead to an increase in the star's
numbers. Vine (1970) also see the cause of outbreaks as a natural periodic
phenomenon in the fluctuation of conditions for survival of the star's larvae.
We may agree that all the above phenomena could cause the periodic
fluctuations in the predator's population density, but only on condition that
the pressure of grazers is lacking. But the main objection is that if these
fluctuations are natural they ought to have been recorded before at some
reefs, which actually is not the case. Many facts cannot be explained either
by Kuhlmann's hypothesis. For example, why did some reefs situated amid
areas of the most severe star outbreaks remain safe? Moreover, in such
uninfested zones some reefs heavily exploited by man also remained.
Therefore, the problem of Acanthaster plagues is still one of the most
intriguing and urgent in reef ecology.
As for the measures in the fight against the infestations, stars were
collected by scuba divers. Off eastern Samoa and Okinawa divers collected
hundred thousands of them. There were attempts to stop the moving front
of stars by electrified wire - an electric barrier. A method was also
developed for killing them by injection of copper-sulfate solution by divers
(Chesher 1969; Sale et al. 1976). But all these measures appeared to be only
palliative and extremely expensive. To kill one star on the reef cos ted 35