|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1997 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1996 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1995 : ¥1,300,000 (Direct Cost : ¥1,300,000)
1.I set 20-40 plates at 10 study areas around Sesoko Island in May, 1997 as same as 1995 and 1996. These plates were collected in September (3 months after setting), and the number of species and the number of individuals were counted in each plate. The most abundant species belong to the genus Acropora occupied over 95% of the total, subordinally species of Pocilloporide, such as Stylophora and pocillopora, were abundant. Juveniles of Porites were rarely observed. This monitoring has been continued from 1989 for 9 years. The most dense settlement, 10,000-30,000/m^2 was observed in 1996 and this was caten times of the normal density. However, the density of settlement returned to the normal density.
2.The population structure of the two dominant species, Acropora hyacinthus and A.digitifera, were studied and analyzed in several areas. The size of main year class of the populations in recoveing areas were different each other. This fact seems to implicate that the years of dominant spats
set were different each other.
3.The relationship between the sea urchins, genus Echinometra, and the density of juvenile corals was studied for analyzing the grazing effect of the sea urchin. The convex relationship was seen between the density of juvenile corals and the density of sea urchin in 1996. However, opposite result, i.e.a concave relationship was observed in 1997, namely the density of juvenile corals was high both at low density and high density of the sea urchin.
4.The predation effect of Acanthaster planci on the population structure of A.hyacinthus was studied using the coral communities both in an enclosure (sea star free) and in the surrounding area (sea star area). Attack of the sea star was intensive around the enclosure (sea star area) in 1996, so that the density and the population structure were suddenly changed in the surrounding area. However, the continuous strucure was observed on the population in the enclosure.
The results of other experiments are analyzing now. Less