396
Destruction and Recovery of Reef Systems, Reef and Man
out of their total number of 152 (Endean and Stablum, 1973 Ormond and
Cambell, 1974; Moran et al. 1985). At 18 of them mass mortality of corals
killed by stars was recorded. At 36 reefs large aggregations of them were
observed and signs of their attacks on corals were visible. But at 26 reefs
situated near the infested ones the stars were absent. Another review
revealed that in a section of the GBR between 14° and 20° out of 240 reefs
over 150 were infested. At the beginning of the 1970s large hordes of stars
appeared on reefs to the north of 14° S up to 12° S, and on many of the
Swane reefs in the southern-section of the GBR (Endean and Stablum
1975). Among the worst destroyed during this period were the reefs of
Green Island. The number of stars on them in 1966 was estimated to be ca.
2 million. Over 2.5 years the stars practically exterminated scleractinian
corals on them (Endean 1973, 1976). After they had destroyed the coral
communities at most of the reefs in the central GBR region, by the middle
1970s their density started to decrease. Till 1977 it remained high only in the
south at some of the Swane reefs. But in 1979-1981 reefs of the central
GBR, previously also damaged by Acanthaster, were subjected to a
repetition of its invasion, as it had been predicted by R. Endean (1977). The
young corals which started to grow on them were attacked by stars again in
1977-1982 (Kenchington and Pearson 1981; Endean and Cameron 1985;
Fisk et al. 1988; Reichelt et al. 1990). So a dangerous tendency of
permanent infestations seems to be developing, which could result in a
gradual irreversible degradation or a drastic transformation of the
ecosystems in vast reef regions.
Populations of Acanthaster, which have a density over 150-200 sp. ha- 1
destroy scleractinian coral communities in the space of 1 to 6 years. For
example, at the fringing reef off Guam Island on a stretch 38 km long over
90% of the corals were killed by stars during the time of only 2.5 years
(Chesher 1969). The extermination of corals was most severe at leeward
fiats, in patch-reef zones and at outer reef slopes. Corals living in the
windward surf zones, where the waves impeded the stars holding on to coral
heads suffered less (Endean 1973). The stars avoid the hydrocoral
Millepora, which has powerfu cnidicil. They practically do not eat the
octocoral Heliopora and rarely attack large, round, massive corals, which
are difficult for them to hold onto. On reefs, where the ramose corals
Pocillopora and Stylophora are defended by their infaunal symbionts, the
stars avoid these too. Rarely are the poritids attacked by stars, which are
loaded full with various structural lipids and contain toxic substances. Only
5 cm 2 of surface area on a massive coral colony damaged by the star causes,
in most cases, its death (Bak and van Eys 1980). An exact account of the
percentage of coral mortality at some reefs of the GBR attacked by
Acanthaster gave its level with 60-90% (Endean and Cameron 1985). On
the Brewer reef in the same region out of the young corals that had
appeared after the 1970-1972 attack, after the repeated attack by stars in
the middle of 1983, 90-95% were killed (Moran et al. 1985). Once all corals
Destruction and Recovery of Reef Systems, Reef and Man
out of their total number of 152 (Endean and Stablum, 1973 Ormond and
Cambell, 1974; Moran et al. 1985). At 18 of them mass mortality of corals
killed by stars was recorded. At 36 reefs large aggregations of them were
observed and signs of their attacks on corals were visible. But at 26 reefs
situated near the infested ones the stars were absent. Another review
revealed that in a section of the GBR between 14° and 20° out of 240 reefs
over 150 were infested. At the beginning of the 1970s large hordes of stars
appeared on reefs to the north of 14° S up to 12° S, and on many of the
Swane reefs in the southern-section of the GBR (Endean and Stablum
1975). Among the worst destroyed during this period were the reefs of
Green Island. The number of stars on them in 1966 was estimated to be ca.
2 million. Over 2.5 years the stars practically exterminated scleractinian
corals on them (Endean 1973, 1976). After they had destroyed the coral
communities at most of the reefs in the central GBR region, by the middle
1970s their density started to decrease. Till 1977 it remained high only in the
south at some of the Swane reefs. But in 1979-1981 reefs of the central
GBR, previously also damaged by Acanthaster, were subjected to a
repetition of its invasion, as it had been predicted by R. Endean (1977). The
young corals which started to grow on them were attacked by stars again in
1977-1982 (Kenchington and Pearson 1981; Endean and Cameron 1985;
Fisk et al. 1988; Reichelt et al. 1990). So a dangerous tendency of
permanent infestations seems to be developing, which could result in a
gradual irreversible degradation or a drastic transformation of the
ecosystems in vast reef regions.
Populations of Acanthaster, which have a density over 150-200 sp. ha- 1
destroy scleractinian coral communities in the space of 1 to 6 years. For
example, at the fringing reef off Guam Island on a stretch 38 km long over
90% of the corals were killed by stars during the time of only 2.5 years
(Chesher 1969). The extermination of corals was most severe at leeward
fiats, in patch-reef zones and at outer reef slopes. Corals living in the
windward surf zones, where the waves impeded the stars holding on to coral
heads suffered less (Endean 1973). The stars avoid the hydrocoral
Millepora, which has powerfu cnidicil. They practically do not eat the
octocoral Heliopora and rarely attack large, round, massive corals, which
are difficult for them to hold onto. On reefs, where the ramose corals
Pocillopora and Stylophora are defended by their infaunal symbionts, the
stars avoid these too. Rarely are the poritids attacked by stars, which are
loaded full with various structural lipids and contain toxic substances. Only
5 cm 2 of surface area on a massive coral colony damaged by the star causes,
in most cases, its death (Bak and van Eys 1980). An exact account of the
percentage of coral mortality at some reefs of the GBR attacked by
Acanthaster gave its level with 60-90% (Endean and Cameron 1985). On
the Brewer reef in the same region out of the young corals that had
appeared after the 1970-1972 attack, after the repeated attack by stars in
the middle of 1983, 90-95% were killed (Moran et al. 1985). Once all corals