The reef morphology and the changes in coral community at West Bise

Reef morphology

The reef of West Bise is exposed to strong wave action from the outer ocean throughout a year. The upper reef slope has a developed spur-and-groove structure, but the lower reef slope deeper than 3-4m has relatively smooth undulation. A tidal current along the reef slope tends to be strong.

Changes in coral community

In 1972, it was reported that coral communities near West Bise had been suffering predation by a large aggregation of the Crown-of-Thorns Starfish. The communities almost completely disappeared by the early 1980s, as coral cover reported in 1984 was 1-3%. A large number of Acropora colonies (ca 20cm in diameter) were observed on the upper reef slope in 1988. Coral cover at shallow parts was as high as 40%, but it decreased with increasing depth down to 2%. Coral cover of these Acropora communities still remained relatively high (>50%) in 1990 when the Environment Agency conducted a nationwide coral reef survey. Coral cover data obtained in our survey using a 5m x 5m quadrat decreased to 5% in 1998 from 20% in 1994. This was due to the mass bleaching event. The recovery of coral community at West Bise was the fastest among all survey sites. In the period between 2006 and 2012, coral cover at the depth of 3m and 10m increased to 16.3% (3m) and 28.1% (10m) from 4.4% (3m) and 9.0% (10m), respectively. This rapid increase was mainly due to the growth of Pocilloporid and Faviid corals.