The Acanthaster Problem
393
in the above manner 2-3 lots of the coral's surface, most often at various
colonies. But when the infestation proceeds and their papulations become
dense (5-lOsp.100m- 2 ), the stars feed throughout the day and each eats up
about 160 cm 2 day-l of the coral's surface. In this conditions one star eats
6-12 m -2 per year of dense coral cover. On their way within the "front"
moving through the reef, the stars kill up to 80-90% of all scleractinian
corals, leaving behind what is actually dead reef (Chesher 1969, Endean
1979).
In experiments, the stars displayed a definite preference lowards prey
corals. They preferred the species of Pocillopora, Acropora and Faviids and
avoided the poritids. But in very dense aggregations they attacked even the
latter. Under natural conditions their preference depends also upon
turbulence conditions. In the surf zones the stars prefer ramose colonies, on
which they hold themselves better. But in calm zones they attack also the
massive corals, on which they cannot stay in the surf zones (Campbell and
Ormond 1970; Cameron et al. 1989). Sometimes they avoid also the large
old colonies of Pocillopora, while in experiments this coral is among the
most "beloved" by stars. It appeared that they are defended by the
symbiotic crabs Trapezia and the shrimps Alpheus, which live in colonies of
Pocillopora (Glynn 1976, 1981, 1984). The hydrocoral Millepora is avoided
by stars being defensed by its powerful nematocysts (Lewis, 1989).
The stars A. planci are bisexual. Once a year they assemble in large
aggregations for the purpose of multiplication. They cast out eggs and
sperem into the water. One star produces about 60 million eggs per year.
Their pelagic larvae bipinnaria feed on phytoplankton (Fig. 11.1). After 3
weeks they settle and transform into the crawling larvae brachiolaria, which
feed on coralline algae (Yamaguchi 1973; Lucas 1973). Passing through their
metamorpothosis, the larvae develop up to the stage of young stars with five
rays, which start to feed on corals. Half a year after their hatching the young
stars attain the size of 1-1.5 cm. The rate of their growth is 1-3 cm per
month (Olson, 1987). In 2-3 years since their settling the star becomes
mature, having a size of 20-30 cm (Kenchington 1977). The percentage of
survival of Acanthaster larvae is very low, just as in any large predator.
Their populations are represented mainly by adults. Their pelagic larvae are
grazed out by zooplankton and fish. The spawn and the settled young stars
are eaten by omnivorous and predatory trochid, muricid and conid
gastropods (Endean 1973). The adult stars, although well defended, are
eaten anyway by some large predatory gastropods, like Charo,!ia tritonis,
and, probably, Cassis cornuta, and by fish like some balistids (Pseudobalistes
jlavimarginatus), tetradontids (Arothron hispidus), and groupers (Cheilinus
undulatus). The most specialized predator among them is Charonia triton is ,
which feeds exclusively on large stars and on holothurians. When attacking
the Acanthaster, this gastropod, with the aid of a peak at the edge of its
shell, turns the star over and grazes it out from its unprotected ventral side.
In experiments, one specimen of Charonia killed up to ten Acanthaster per
393
in the above manner 2-3 lots of the coral's surface, most often at various
colonies. But when the infestation proceeds and their papulations become
dense (5-lOsp.100m- 2 ), the stars feed throughout the day and each eats up
about 160 cm 2 day-l of the coral's surface. In this conditions one star eats
6-12 m -2 per year of dense coral cover. On their way within the "front"
moving through the reef, the stars kill up to 80-90% of all scleractinian
corals, leaving behind what is actually dead reef (Chesher 1969, Endean
1979).
In experiments, the stars displayed a definite preference lowards prey
corals. They preferred the species of Pocillopora, Acropora and Faviids and
avoided the poritids. But in very dense aggregations they attacked even the
latter. Under natural conditions their preference depends also upon
turbulence conditions. In the surf zones the stars prefer ramose colonies, on
which they hold themselves better. But in calm zones they attack also the
massive corals, on which they cannot stay in the surf zones (Campbell and
Ormond 1970; Cameron et al. 1989). Sometimes they avoid also the large
old colonies of Pocillopora, while in experiments this coral is among the
most "beloved" by stars. It appeared that they are defended by the
symbiotic crabs Trapezia and the shrimps Alpheus, which live in colonies of
Pocillopora (Glynn 1976, 1981, 1984). The hydrocoral Millepora is avoided
by stars being defensed by its powerful nematocysts (Lewis, 1989).
The stars A. planci are bisexual. Once a year they assemble in large
aggregations for the purpose of multiplication. They cast out eggs and
sperem into the water. One star produces about 60 million eggs per year.
Their pelagic larvae bipinnaria feed on phytoplankton (Fig. 11.1). After 3
weeks they settle and transform into the crawling larvae brachiolaria, which
feed on coralline algae (Yamaguchi 1973; Lucas 1973). Passing through their
metamorpothosis, the larvae develop up to the stage of young stars with five
rays, which start to feed on corals. Half a year after their hatching the young
stars attain the size of 1-1.5 cm. The rate of their growth is 1-3 cm per
month (Olson, 1987). In 2-3 years since their settling the star becomes
mature, having a size of 20-30 cm (Kenchington 1977). The percentage of
survival of Acanthaster larvae is very low, just as in any large predator.
Their populations are represented mainly by adults. Their pelagic larvae are
grazed out by zooplankton and fish. The spawn and the settled young stars
are eaten by omnivorous and predatory trochid, muricid and conid
gastropods (Endean 1973). The adult stars, although well defended, are
eaten anyway by some large predatory gastropods, like Charo,!ia tritonis,
and, probably, Cassis cornuta, and by fish like some balistids (Pseudobalistes
jlavimarginatus), tetradontids (Arothron hispidus), and groupers (Cheilinus
undulatus). The most specialized predator among them is Charonia triton is ,
which feeds exclusively on large stars and on holothurians. When attacking
the Acanthaster, this gastropod, with the aid of a peak at the edge of its
shell, turns the star over and grazes it out from its unprotected ventral side.
In experiments, one specimen of Charonia killed up to ten Acanthaster per