Studies on the conservation and management of coral reefs and the control of Acanthaster planci juveniles.

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This primary study was made for conservation and management of coral reefs and control of Acanthaster Planci during the years 1985 to 1988 in the northwestern Iriomote Island, Ryukyu Islands. Coral reefs of the area has been badly damaged by the starfish by 1985. At present, coral recovery are in progress.Weight increment of four common Acroporid corals was faster in shallow or clear waters (around 0.7 %/day) than in deep or turbid waters (around 0.4 %/day). Acropora nobilis was calculated to increase 0.79 - 1.08 m^2 of surface area in a year.Breeding season of A. planci was from late May to the middle of June. Its embryos developed faster at temperatures of 28 - 32 ゜C than at 20 - 26 ゜C. Its hatching occurred 11 - 13 hours after the insemination at 28 - 32 ゜C and 33 hours at 20 ゜C. Planktonic larvae of starfishes occurred from June to August. The algae-feeding Acanthaster juveniles were collected mostly on the reef slopes from July. Its density was highest (0.82/ind./m^2) in 1986 and much lower in the following years. The cohorts of 1986 and 1987 switched their food to coral at ages of 9 - 11 months (15 - 25 mm in diameter). Their growth rates were 2 - 3 mm/month in algae-feeding phase and 8 - 15 mm/month in coral-feeding phase. A part of the 1986 cohort matured in two years.Drupella cornus was the commonest among 11 species of coral-feeding gastropods identified. Its maximum feeding rate for Acropora was 5.8 cm^2/ind./day.The present findings of Acanthaster juveniles would contribute to the forecast of the outbreaks and to the possibility of commencing the control program in earlier stage of the outbreaks. Though A. planci is the most harmful to the reef corals, other predators including the gastropod should be taken into account when coral reefs are recovering.