The 1997-1998 Mass Bleaching Event Around the World

Pacific Ocean (west)

Throughout the bulk of the Pacific, water temperatures were close to normal during 1997 and 1998, however up against the Australian mainland, warmer temperatures were recorded in January and February, 1998. The majority of the bleaching over the Great Barrier Reef peaked during the last two weeks of February. This did not coincide directly with El Nino, which normally means warmer temperatures in the east Pacific, not the west. The similarity of 1988 and 1998 bleaching, especially in the eastern hemisphere, makes a case for a possible indirect relationship to El Nino. Later in the year in the northern summer, warm water appeared in the far northwest Pacific around Japan and Philippines in July, around Taiwan in August and Palau in September. Typhoons late in the season (September to October) resulted in reductions in temperatures as the high winds and waves mixed warm surface waters with cooler waters from the deep.

Australia

Sea surface temperatures warmed considerably off eastern Australia during early 1998. Aerial surveys of 654 reefs show that extensive bleaching occurred along the entire length of the Great Barrier Reef (GBR) from Elford Reef (17^oS), to Heron Island (23^oS). The intensity of bleaching was much greater on inshore reefs than mid-shelf or outer-shelf reefs. Overall 87% of inshore reefs showed at least some bleaching, compared to 28% of offshore reefs. Heavy bleaching was seen on 55% of inshore reefs (with greater that 30% coral cover), compared to 5% of offshore reefs. However, ground truth surveys suggest that these figures are conservative.

Over 100 coral species bleached, including bleaching and partial death of large Porites colonies that were centuries old. This bleaching appeared to be a combined effect of raised temperatures, exacerbated in the central GBR by massive flows of rainwater in January. Soft corals were extensively bleached on these inner reefs with almost all species bleached. In the upper 5 m, soft corals are 100% bleached and about 20% bleached at 8-12 m depth. Mortality was high, even in the normally resistant Sinularia. On Orpheus Island, between 84% and 87% of corals bleached, but 5 weeks later, mortality was between 2.5 and 17%, with the Acropora species being most affected. Pocillopora species were hardly affected. However, 10 km away on Pandora reef, there was virtually 100% mortality of corals down to 6 m depth, where bleaching followed both a temperature rise and extensive fresh water flows over the reef.

In March, bleaching also extended to southern Queensland (Gneering Shoals; 26^oS) and northern New South Wales (28°30'S) on rocky reefs with populations of corals up to 50% coral cover. Water temperatures were around 28°C (maybe as high as 30°C), whereas they are normally in the mid 20^oCs. Pocillopora damicornis and Stylophora pistillata were most affected with 60-70% of these species bleached to 15m depth. In the central GBR, inshore average daily sea temperatures near Townsville exceeded 31.5°C on the reef slope (the likely local bleaching threshold) at 6 m on 12 days and reached a maximum of 32.7°C. No bleaching was observed on the Flinders Reefs (27^oS), between these two sites.

(Andrew Baird, Simon Banks, Ray Berkelmans, Daniel Bucher, Lyndon Devantier, Katharina Fabricius,)

Fiji

No bleaching was seen during the past year over about 180 km on the South side of the Great and North Astrolabe Refs (18^oS), which have extensive coral cover.

(Joan Koven)

Federated States of Micronesia

About 20% of corals bleached down to 20 m on the northwest and northeast side of Yap, in the beginning of September 1998. Many Genera were observed to bleach including: Acropora, Goniastrea, Platygyra, Diploastrea, Mycedium, Goniopora, Porites (massive), Physogyra, Psammocora, Montipora, Pocillopora, Turbinaria, Hydnophora, Astreopora, Echinopora, Stylophora, Favia, Leptoria, Seriatopora, Pavona, and Fungia. Soft corals (Sarcophyton, Lobophyton), anemones (Heteractis), and Heliopora also bleached. Water temperatures were 30-3 ^oC. No bleaching was seen in the lagoon in Chuuk.

(Sandra Romano)

French Polynesia

During a bleaching event on Moorea in 1991, 20 % of corals died on the outer slopes, and during another in 1994 bleaching was less severe and more dispersed. Monitoring on another 14 islands has been added to Moorea as a contribution to the GCRMN. Bleaching in early 1998 was variable among atolls and in locations on atolls. Strong bleaching was seen in some areas like Takapoto, where 20% coral cover in 1994 was reduced to 12% after 1998 bleaching. There was also severe bleaching on Rangiroa and Manihi with significant mortality. On Moorea and Bora Bora, coral cover remains at 30 to 50% (normal for French Polynesian outer slopes at 15 m) with minimal bleaching, if any. Non-bleaching mortality was seen on Tikehau Atoll, with a drop in coral cover from 40% in 1994 to 4% in 1998 because of strong cyclonic waves.

(Yannick Chancerelle, Bernard Salvat)

Hawaii

No bleaching was seen in Hawaii and this has been the coldest summer measured (average close to 26 ^oC).

(Cindy Hunter)

Johnston Atoll

No bleaching was seen, but there was evidence of recovery from a bleaching event a few years earlier. These reefs have nearly 100% live coral cover in suitable areas. No elevated water temperatures were observed by satellite.

(Les Kaufman)

Palau

Major coral bleaching occurred in Palau in September, 1998 with water temperatures from 30-32^oC. About 75% of corals shallower than 15 m bleached, and in Arakabasan and one of the rock islands (‘Cemetary’) there was 20-70% bleaching and high mortality. The eventual impact is not known, but the area looks awful. About 70-80% of the corals were bleached down to 30 m off of Peleliu, the Blue Corner, the Big Drop-off (all in the south), as well as Iwayama Bay in the Rock Islands near Koror. Everything that could bleach was bleaching. The hard corals were not yet dead for the most part, but many of the soft corals were dead. This was in mid-September, and there was minimal bleaching at the ‘Blue Hole’.

(Pat Colin, Eric Guinther, Sandra Romano)

Papua New Guinea

Water temperatures below 10 m around Kimbe Bay (New Britain) in August 1998 were 31-31.5°C, and on the surface they were 32-33 °C. High mortality of corals was observed with 75% of Acropora affected, and bleaching in many other genera including Porites, Platygyra and Montipora. Some others were partially bleached, and effects were observed down to 50 m. On the southwest side of Kimbe Bay, water was 29.5 to 30°C, and there was only 10% bleaching of Acropora and only isolated cases of bleaching on other species.

In March 1998, large areas of reefs south of Normanby Island through to Cape Vogel, and Tufi (far southeast PNG) showed coral bleaching from mid-February. Bleaching extended down to 20 m, but was most extensive in shallow water (almost 100% in some areas, including soft corals and anemones). Water temperatures were 29-30^oC from December to February, which is not exceptional for Milne Bay. Reefs to the north Normanby and Fergusson Ids were apparently not affected by any bleaching.

(James Cervino, John Rewald)

Samoa (Western)

Between 60 to 70% of all Acropora on the reef top bleached within 5-6 days just before the end of February 1998, at Palolo Deep, National Marine Park near Apia. Corals in deeper water appeared healthy. Some bleaching in Samoa was linked to extreme low tides and exposure to air.

(Mike King)

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Last updated - 7 December 98

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