MEPS 239:93-103 (2002)  -  doi:10.3354/meps239093

Recovery of coral populations after the 1998 bleaching on Shiraho Reef, in the southern Ryukyus, NW Pacific

Hajime Kayanne1,*, Saki Harii2, Yoichi Ide3,**, Fujio Akimoto4

1Department of Earth and Planetary Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan
2Department of Mechanical and Environmental Informatics, Tokyo Institute of Technology, Ookayama, Tokyo 152-8552, Japan
3Marine Ecological Institute Co. Ltd., Haradamotomachi, Osaka 561-0808, Japan
4Fuyo Ocean Development & Engineering Co. Ltd., Kuramae, Tokyo 111-0051, Japan
*E-mail: **Present address: Oceanic Planning Corporation, Kasuya, Fukuoka 811-2304, Japan

ABSTRACT: The most extensive and severe bleaching of coral ever recorded occurred in 1997 and 1998 as a result of anomalously high sea-surface temperatures. In the Ryukyu Islands, extensive bleaching occurred from late July to early October in 1998. A time-series transect study on a reef flat revealed the different responses of coral populations among species to this event. Coral cover was monitored just before, during, and 6 times after the bleaching occurred, along 5 fixed transects, 710 to 800 m long, across the reef flat of Shiraho Reef, Ishigaki Island, in the Ryukyu Islands of Japan. The dominant corals were Heliopora coerulea, massive Porites, and branching Porites, Montipora, Acropora, and Pavona (these latter 4 genera could not always be distinguished to species level, and are thus grouped by genus and ecoform). H. coerulea was the least susceptible to bleaching and maintained almost constant coverage before and after the bleaching. Massive Porites were susceptible to bleaching, but regained their algae after the bleaching and sustained their coverage. On the other hand, the branching Porites, Montipora, and Acropora were susceptible to bleaching and mortality was high. Coverage by branching Montipora was initially reduced by 66%, but by 2 yr after the bleaching it had recovered to pre-bleaching coverage. However, only large patches of more than 70 m along a transect, with coverage of 10 to 40%, recovered. Small patches of less than 30 m along a transect, with coverage of less than 10%, died and did not recover. The response of corals to bleaching differs according to the strategy the coral uses against bleaching; moderately frequent and severe bleaching might permit the coexistence of both types of corals on the same reef flat, as in the case of Shiraho Reef.

KEY WORDS: Coral reef · Bleaching · Recovery · Population · Ryukyu Islands

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