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8,630,000 Yen (FY1996 2,998,000 Yen)
Field investigation on the distribution and community structure of hermatypic corals has been conducted at ten study sites within the vicinity of the Urasoko Bay, using the line transect and the quadrat methods. Hermatypic corals of 16 families 56 genera 229 species were identified within the Urasoko Bay. The number of species, the number of colonies, and the coral coverage increase from the coastal side to the offshore reef flat. The distribution pattern of the corals exhibited uniform or random one on the offshore reef flat and aggregated near the coastal side. The species and generic composition also differed each other in relation to their environmental conditions; the genus Acropora became dominant on the offshore reef flat, while the genus Montipora and Porites near the shore of the bay. It is considered that such diversity was caused by the complicated coral reef topography and by the wide ranges of environmental gradients.
Concentric environmental gradients of turbidity, transparency, salinity and the quality and quantity of sediments were observed from the coastal side to the offshore reef flat. They changed both vertically and horizontally according to ebb and flow. Bleaching caused by the high water temperature was hardly observed in 1995-1996, unlike in 1993-1994, in relation to slightly low water temperature during the summer.
Good inhabiting conditions for the survival of hermatypic corals are maintained on the offshore reef flat. In contrast coral, communities could not recover from damage by crown-of-thoms starfish because of much sedimentation in the coastal side of the bay.
Coral, Coral Reef, Sediment, Bleaching, Community