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

Reef morphology

The reef of North Bise is characterized by well-developed spur-and-groove system. Narrow spurs and deep grooves form comb-like structure on the upper reef slope (2-7m depth). There is a basin-like topography that is parallel to the reef crest at the depth of 8m. Then the lower reef slope becomes gradual.

Changes in coral community

A broad-scale survey of Okinawa Island conducted in 1972 did not cover North Bise site, but the situation was probably similar to that in West Bise where coral community partially suffered predation of the Crown-of-Thorns Starfish. In 1984, coral community around Cape Bise had been devastated. Coral cover at that time was reported to be 3% at most. The coverage of coral community mainly comprised of Acropora and Pocillopora gradually increased in the late 1980s and it reached 20-30% in 1992. These coral communities suffered extreme bleaching and mortality in 1998 and they had never recovered by 2004. In the period between 2006 and 2012, coral cover at the depth of 3m and 10m increased to 9.7% (3m) and 13.2% (10m) from 2.8% (3m) and 4.7% (10m), respectively. This increase seemed to indicate the coral recovery, but a large proportion of the coral communities was comprised of non-Acroporid corals.