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[D-4.1.2 Effects of Environmental Stresses on Corals]

[Contact Person]

Michio Hidaka
Department of Chemistry, Biology, and Marine Sciences University of the Ryukyus,
Nishihara-cho, Okinawa, 903-01 Japan
Tel:+81-98-895-8547, Fax:+81-98-895-5376
E-mail:hidaka@sci.u-ryukyu.ac.jp

[Total Budget for FY1994-1996]

8,727,000 Yen (FY1996 2,757,000 Yen)

[Abstract]

　The purpose of the present research is to find out suitable indices of coral health, to study effects of nutrient enrichment on coral growth rate, and to study the mechanism of bleaching of corals. The rates of calcification and photosynthesis, density of zooxanthellae as well as sugar and lipid contents appeared to be good indices of coral health. High concentrations of ammonium affected coral growth rates even when zooxanthellae density was not changed. The morphology of zooxanthellae in the coral Galaxea fascicularis exposed to various stresses was compared with that of zooxanthellae expelled from the host. Isolated zooxanthellae exposed to the same stresses were also studied, The degradation process of zooxanthellae varied depending on the type of stresses. Degraded zooxanthellae were selectively expelled by the host when the coral was treated with high temperature or strong light.

[Key Words]

Bleaching, Coral, Zooxanthella, Environmental stress