The Acanthaster Problem
397
on a reef are eaten, the stars may move to the neighboring one advancing on
the bottom between them at depths down to 60 m (Endean and Stablum
1973). At isolated reefs, after the extermination of corals the stars for a long
time still remain on the reefs. Then they gradually die out.
After an Acanthaster invasion only white skeletons of scleractinians
remain. Then they are overgrown by filamentous algae and covered with
black patches of slimy colonies of blue-green algae. The coral's infauna dies.
Fish abandon the destroyed reefs which present a pitiful picture to the
observer. The colonies of killed corals are later attacked by boring animals
and gradually collapse (Chesher 1969). Instead of a flourishing reef, 2-3
years after the stars' attack only heaps of rubble and the rare colonies of
dead massive corals covered by alcyonaceans remain. Later on, such killed
reefs are most often inhabited by alcyonaceans, which form on the reef flat a
continuous cover. The surface of massive corals is overgrown by incrusting
Sinularia, and amid the rubble colonies of Sarcophyton, Lemnalia and
Paralemnalia appear in mass. Thus in the place of exterminated reef usually
alcyonacean associations are forming, which continue to exist sometimes for
several years preventing the restarting of scleractinian growth (Endean and
Stablum 1973; Nishihira and Yamazato 1974; Cameron and Endean 1981).
This author has observed this scenario on the reefs of Lizard Island (GBR),
where formerly beautiful reefs were attacked by Acanthaster in the early
1970s But even in 1986 most of the reef-flat areas there were occupied by
thickets of ugly alcyonaceans without any sign of recovery of scleractinian
populations.
On the fields of rubble, which remain on the destroyed reef, the
filamentous algae are later gradually replaced by coralline algae, at which
point the recruitment of new scleractinian populations starts and their new
colonies begin to grow. Among them the most numerous are the
opportunistic fast-growing specises of Acropora, Pocillopora, Seriatopora,
Turbinaria and Montipora. The more reef has been damaged, the later starts
the recovery of scleractinian corals (Endean 1973; Endean and Stablum
1975). On one of the platform reefs of the GBR, destroyed by stars, even 7
years after the invasion the percentage of its cover by coral was only 3%,
while before the invasion if had been about 30%. Most corals in this
recovering community were represented by large colonies of Porites and
Diploastrea, which survived the invasion, and by the newly appearing young
colonies of Acropora, which numbered about 60m- 2 (Pearson 1974). About
10-15 years after invasion, in reef areas where scleractinians had managed
to replace alcyonaceans, their communities were composed of average-sized
ramose and foliose colonies and had a low species diversity. These
regenerating communities are poor in large massive corals and are not
resistant to the surf. So they were susceptible to destruction during strong
storms, and also endangered by the repetition of Acanthaster attacks. In
such permanently inhibited "ill" reef communities bioerosion could
overwhelm the calcification processes, as it was pointed out by first
397
on a reef are eaten, the stars may move to the neighboring one advancing on
the bottom between them at depths down to 60 m (Endean and Stablum
1973). At isolated reefs, after the extermination of corals the stars for a long
time still remain on the reefs. Then they gradually die out.
After an Acanthaster invasion only white skeletons of scleractinians
remain. Then they are overgrown by filamentous algae and covered with
black patches of slimy colonies of blue-green algae. The coral's infauna dies.
Fish abandon the destroyed reefs which present a pitiful picture to the
observer. The colonies of killed corals are later attacked by boring animals
and gradually collapse (Chesher 1969). Instead of a flourishing reef, 2-3
years after the stars' attack only heaps of rubble and the rare colonies of
dead massive corals covered by alcyonaceans remain. Later on, such killed
reefs are most often inhabited by alcyonaceans, which form on the reef flat a
continuous cover. The surface of massive corals is overgrown by incrusting
Sinularia, and amid the rubble colonies of Sarcophyton, Lemnalia and
Paralemnalia appear in mass. Thus in the place of exterminated reef usually
alcyonacean associations are forming, which continue to exist sometimes for
several years preventing the restarting of scleractinian growth (Endean and
Stablum 1973; Nishihira and Yamazato 1974; Cameron and Endean 1981).
This author has observed this scenario on the reefs of Lizard Island (GBR),
where formerly beautiful reefs were attacked by Acanthaster in the early
1970s But even in 1986 most of the reef-flat areas there were occupied by
thickets of ugly alcyonaceans without any sign of recovery of scleractinian
populations.
On the fields of rubble, which remain on the destroyed reef, the
filamentous algae are later gradually replaced by coralline algae, at which
point the recruitment of new scleractinian populations starts and their new
colonies begin to grow. Among them the most numerous are the
opportunistic fast-growing specises of Acropora, Pocillopora, Seriatopora,
Turbinaria and Montipora. The more reef has been damaged, the later starts
the recovery of scleractinian corals (Endean 1973; Endean and Stablum
1975). On one of the platform reefs of the GBR, destroyed by stars, even 7
years after the invasion the percentage of its cover by coral was only 3%,
while before the invasion if had been about 30%. Most corals in this
recovering community were represented by large colonies of Porites and
Diploastrea, which survived the invasion, and by the newly appearing young
colonies of Acropora, which numbered about 60m- 2 (Pearson 1974). About
10-15 years after invasion, in reef areas where scleractinians had managed
to replace alcyonaceans, their communities were composed of average-sized
ramose and foliose colonies and had a low species diversity. These
regenerating communities are poor in large massive corals and are not
resistant to the surf. So they were susceptible to destruction during strong
storms, and also endangered by the repetition of Acanthaster attacks. In
such permanently inhibited "ill" reef communities bioerosion could
overwhelm the calcification processes, as it was pointed out by first