Status of Coral Reefs of the World 2000

Status of Coral Reefs of the World: 2000
CASE STUDY 4: BLEACHING ON THE REEFS OF SOUTHERN JAPAN
There was unprecedented mass coral mortality in Okinawa, Japan, with the local
extinction of at least 4 coral species and a loss of hard and soft coral cover from 70%
to 10%. A strong La Niña coincided with mid summer, no typhoons and low cloud cover
and this raised water temperatures around Okinawa to 2.8 o C above the 10 year
average. Bleaching started in mid-July and ended with the first typhoon of the season
in September. Locals reported seeing nothing like this during the 35 years of coral reef
research, and elderly Okinawans said they “have never seen such beautiful white corals”.
Coral cover virtually did not change between 1995 and 1997 at Sesoko Island
(26 o 38’N, 127 o 52’E), but after the bleaching, mean coral cover decreased by 73%,
the number of species decreased by 61% and number of colonies per m 2 dropped to
less than half. Furthermore the living cover of soft corals decreased by 99%. Branching
Acropora species which were once the most prolific corals on Okinawan reefs, were
most severely affected; 3 species of branching corals species (Seriatopora hystrix, S.
caliendrum, Stylophora pistillata and Pocillopora damicornis) and the branched fire
coral Millepora intricata are now locally extinct and no new recruits were found around
Okinawa in 1999. Curiously, many juvenile Acropora colonies (< 5cm in diameter)
survived on the reef flats, where they are likely to be killed when exposed to air and high
irradiance during midday low tides. Bleaching also affected other common corals, whereas
many of the less common species survived and are now the most abundant e.g. massive
and encrusting colonies of Porites, Goniastrea, Leptastrea, Platygyra, Favia and Favites.
The chances for recovery of the missing species depends on coral populations on distant
offshore reefs (15-30km from Okinawa) which may provide larvae for re-settlement,
provided currents are favourable.
Report from Yossi Loya Department of Zoology, Tel-Aviv University, Israel 69978, e-mail:
yosiloya@post.tau.ac.il
impacts were often minor on inshore areas which experience natural variations in
temperature and water clarity. On the northern Ngeruangel atolls, bleaching deaths varied
between 10% and 70% at all depths, with a mean of 53.4% of corals at 3–5m, 68.9% at
10–12m, and 70% at 30m (Peleliu, the Blue Corner, the Big Drop-off, Iwayama Bay - Rock
Islands). Severe bleaching occurred in Arakabasan and Cemetary island. The major damage
was to corals in oceanic waters, with much less bleaching and mortality in shallow areas
and close to the more turbid and stressed habitats near the shore. The least effect was to
corals around the sewage outfall near Koror (John Bruno, e-mail: John_Bruno@Brown.edu).
All adult jellyfish in the famous marine lake (Ongeim’l Tketau) were killed, but live polyps
were found in 1999.
About 20% of corals, including a wide variety of hard and soft coral species, bleached to
20m depth on the north of Yap, Federated States of Micronesia in September 1998,.
Other parts of Micronesia reported only minor bleaching.
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