The evolution of a Holocene fringing reef and island: reefal environmental sequence and sea level change in Tonaki Island, the Central Ryukyus

Coral Reef Evolution at the Leeward Side of Ishigaki Island, Southwest Japan

“…Thus, the framework facies of the leeward reefs are also similar to those of windward reefs. However, branching Acropora thickets shown in Kan et al (1997a) did not occur in Tonoshiro Reef, as Tonoshiro Reef had no windward reef formation prior to its development.…”

“…Dredging during a fishery port repair in 1985 exposed a submarine trench wall about 300 m in length and 4-7 m in height stretching from the reef edge to the moat of this modern fringing reef (Figure 1c). The trench sites are found elsewhere in the Ryukyu Islands and the Great Barrier Reef of Australia, providing the good opportunity to observe the continuous reef section Hori 1991, 1993;Kan et al 1995Kan et al , 1997a). …”

“…Lateral expansion rates of Tonoshiro Reef (33 and 75 m/ka) are similar to Kabira Reef (58 and 149 m/ka) and another windward reef (37 and 45 m/ka, Kan and Hori 1993). The framework of Tonoshiro Reef (Figure 2) is constructed by in-situ tabular Acropora, which is also shown in the leeward side of Tonaki Reef (Kan et al 1997a). Thus, the framework facies of the leeward reefs are also similar to those of windward reefs.…”

“…Hopley and Barnes (1985) examined the development of a continuous reef (Orpheus Island, the Great Barrier Reef of Australia) stretching from the windward side to the leeward side by an analysis of cores taken from both sides of the reef, and indicated that the leeward reef had formed after the establishment of the windward reef. Kan et al (1997a) examined the leeward side of a continuous reef (Tonaki Reef, Ryukyu Islands) and also suggested the delayed evolution of the reef framework at the leeward side in comparison with the windward side. They revealed that, at the leeward side, abundant branching Acropora thickets formed prior to the establishment of the reef framework.…”

“…Then, upward growth of the reef was terminated due to the stable sea level, and the lateral expansion of the reef occurred. Finally, the backreef structure of the reef flat such as moats, motus, cays, and tombolos have formed by bioclasts derived from the reef framework (McLean and Woodroffe 1994;Kan et al 1997a;Yamano et al 2001). …”