| Budget Amount *help |
¥12,300,000 (Direct Cost: ¥12,300,000)
Fiscal Year 2003: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2002: ¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2001: ¥6,000,000 (Direct Cost: ¥6,000,000)
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| Research Abstract |
The reproductive biology and early life ecology of abalone, Haliotis discus discus, H. madaca, H. gigantea and H. diversicolor, which inhabit in southern area in Japan, were investigated by field observations and laboratory experiments in this study. The factors affecting recruitment of the northern species Haliotis discus hannai, which has more information on its reproduction and ecology in the early life stages than the southern abalone species, were analyzed and discussed.
Epidemic spawning of the small abalone Haliotis diversicolor appeared to be synchronously with typhoon events. The larval settlement and initial survival of post-larvae could be strongly influenced by sediment on the settlement substrata and wave disturbance. The dietary conditions and water temperature in their habitats could affect the survival and growth rates of juveniles. The radula development in H. diversicolor was different from that in H. discus hannai, suggesting the main diets and thus habitat of H. diversicolor are different from those of big abalone species.
Larvae and post-larvae of big southern abalone species, H. discus discus, H. madaca, H. gigantea, appeared from October to January. However, any associated spawning cues were not detected. Densities of the post-larvae of these big species were much lower than that of H diversicolor. Successful reproduction of the big abalone species may be inhibited due to the low density of their spawning populations.
As present major factors affecting recruitment of H. discus hannai, seawater temperature during winter, density of spawning adults, and dietary conditions for post-larvae were suggested.
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