The 1997-1998 Mass Bleaching Event Around the World

Indian Ocean

The extent of bleaching in the Indian Ocean during 1998 is unprecedented in both the extent and severity. Warm surface waters have migrated from south to north during the first 6 months, with considerable coral reef bleaching occurring in each locality. The warm pool of water was observed in satellite images from the National Oceanic and Atmospheric Administration of USA in January 1998, with the first bleaching being seen in April. This bleaching is similar, but more severe than the1987 El Nino in the Indian Ocean, which caused some mortality, but the reefs recovered quite quickly in the Maldives.

Chagos

The atolls apparently escaped bleaching as none has been reported in the past 2 years. No details known.

(Charles Sheppard)

Comores

In late May, bleaching was observed on the 2 islands: Grande Comore (near the airport); and Galawa (near beach hotels). Bleaching was seen from the air, possibly linked to freshwater runoff.

(Jean-Pascal Quod)

India

The outer-atoll seaward slopes of Kadmat in the Lakshadweep Islands, India had live coral cover around 80-90% in places. A Reef Check survey showed heavy mortality with only 3% live coral cover and 87% dead branching and table forms at 3m. At 10m, live coral cover was 7%, with 43% dead coral cover, and 38% rocky substrate. Bleaching at Kavaratti Island, Lakshadweep islands in May appears similar to what was seen in the Maldives, perhaps less severe. Not all reefs in Lakshadweep have been so severely affected. Some bleaching, between 10% to 30%, was seen in the Gulf of Kutch on the northerly Gujarat coast in early to mid-May. Reports are coming of bleaching in the Andaman islands.

(Arjan Rajasuriya, Jason Rubens)

Kenya

Bleaching started north of Lamu (2^oS), on 18 March 1998 when temperatures reached 32^oC and continued during April. Bleaching around Mombasa started around the same time and was as low as 50%, but mostly near 100% on almost all reefs seen, where there had been 20-50% coral cover. Bleaching was most extreme in shallow water, but was also 50% or more at 20 m. Coral mortality ranges between 50 to 90%, with reefs now having 1-10% coral cover, with 10 - 50% of the remaining live corals still bleached in mid-October.

(David Obura)

Madagascar

There was bleaching of 30% of corals at Belo sur Mer (mid-west coast), with water temperatures of 32-33°C in February and March, 1998 and similar bleaching at Antananbe, Toliara, Nosy Bé, Mitsio archipelago, and Mananara-Nord, Masoala peninsula (northeast coast, 15^oS). There was no distinction in species affected at most sites, but at Mananara, Acropora corals in shallow water were 40-80% bleached with high mortality, and 10-40% of mixed species corals bleached in deeper water. Another report from Toliara/Tulear for September was of no bleaching nor crown-of-thorns damage with the reefs in a good state of health.

(Jean Maharavo, David Obura, Charlie Veron)

Maldives

There has been heavy damage to coral reefs in the central tourism region of the Maldives. Relatively severe, rapid bleaching occurred between late April to May, 1998, and now there are signs of partial recovery. Around 80% of corals wholly or partially bleached on the back reef, with around 45% at 10m on the reef slope, and 30-40% at 20 -30m. Bleaching was also seen at 50m. These observations on North Male Atoll have been effectively confirmed by sea-plane operators who observed similar levels throughout the Maldives. Other reports from North Male and the Ari Atoll were of 95% of mostly Acropora communities dead, including soft corals and anemones. Many massive corals are still under stress and partially bleached. Prior to this, coral cover was around 30-50% in shallow water (mostly Acropora), decreasing with depth. Bleaching appears to have killed almost all shallow corals, but effects are less at greater depths, although still severe.

By late May, recovery began for Porites species on South Male and Vaavu Atolls, and colour was near normal by September, but Acropora species suffered major mortality, some times up to 100%. On South Male Atoll, temperatures were high, being over 30°C at 30 m from April to June 1998. Here 100% of some Sinularia soft corals bleached (but not Sarcophyton); corals (Acropora, Fungia and Porites were 60-80% bleached; and even giant clams (Tridacna) were partially bleached. Many anemones have since regained their colour. An apparently similar result was seen in the 1970s, with large areas of reefs dead from unknown causes, but recovery was rapid.

(Jason Rubens, William Allison, Norbert Schmidt, Reto Wyss, Zdenka Vapenik)

Mauritius

There was minor bleaching in Mauritius this year, with some small localised areas of moderate bleaching. Surveys showed from 1-15% bleaching in many locations, and up to 50% corals with minor loss of colour. Temperatures were about 3^oC above the normal of 27^oC. On Iles aux Benities, there was moderate bleaching (about 50% in the lagoon).

(Loic Charpy, Ruby Moothien Pillay)

Mayotte

Corals began to bleach at Mayotte (Comoro Archipelago) in mid-April on the southern end exposed to the tradewinds, and also in the lagoon, which receives cooler water from the north. Very high mortality seen

(maybe 80% of Acropora) on the outer slope, with other main genera affected being Galaxea, Lobophyllia, and Goniopora. Soft corals were also bleached, but Porites were not affected. ‘Many bright corals’ were seen on nearby small coral islands of Europa and Juan de Nova.

(Jean-Pascal Quod, Bernard Thomassin)

Reunion

During the last 2 weeks of March, there was significant bleaching (approx. 30% to 50%) on the reef flats and reef slopes of Reunion, with Acropora, Galaxea and Pocillopora the genera most affected. Water temperatures were high (but not recorded) and there was very heavy rainfall for most of February. No recovery was seen several months later, with corals now covered with turf algae.

(Michel Pichon, Jean-Pascal Quod)

Seychelles

There was extensive bleaching down to 23 m in the south on Aldabra and Providence Group (9^oS; 46 to 51^oE), and Alphonse Group (7^oS; 53^oE) during March-May 1998. Temperatures ranged from 29^oC to 32^oC, and 34^oC in lagoons. Bleaching and mortality affected Acropora, Pocillopora and Millepora, with 40-50% bleached and an additional 20-55% recently dead with significant algal growth. Soft corals (85-95% mortality), anemones and giant clams also bleached. Corals at 14 sites in the Seychelles Marine Park system that were filmed showed that an average of about 75% were recently dead (ranging from 50% to 95%). The dead corals were covered with filamentous algae, which were expanding to cover areas of dying corals. Other reports were of moderate bleaching, which was not exceptional.

(Clare Bradshaw, Loic Charpy, Tom Goreau, Kristian Teleki, Mark Spalding, Tom Spencer)

Sri Lanka

Bleaching started about 10 April 1998 in the southwest at the Hikkaduwa Marine Sanctuary with over 75% bleaching in the beginning, and 90-95% at Buona-vista. Almost all coral species between 1 m and 8 m, except Montipora species were affected when water temperatures went from the normal 29°C to 30°C to about 36°C in mid-April and remained above 32^oC until late May. Bleaching increased to more than 80% on the reef flat by late April, and on deeper offshore reefs off Colombo. All species appear to have been affected, but some soft corals appear to have resisted the bleaching better, but not Sarcophyton and Lobophyton. Bleaching was noticeable down to 42 m on the southeast coast near Battilacoa in mid-May. No bleaching was observed 100 km further up on the northeast coast of near Trincolamalee (Green Bay and Rocky) in May to September with 50-60% live coral cover on the reefs.

Corals remained bleached up to early June 1998, with most branching and tabulate Acropora and Pocillopora colonies starting to die off and be covered by algae. Some recovery (regaining normal colour) of about 10% of bleached corals was observed in mid-July. Recovery at Buona-vista was more extensive with most bleached colonies regaining some colour in late June when monsoon winds resulted in lower temperatures. But the reef possibly lost over 70% of its coral cover. Bleaching like this has never been seen in Sri Lanka before; any bleached corals in the past recovered within 3 to 4 weeks.

(Arjan Rajasuriya, Jason Rubens, Prasanna Weerakkody)

Timor Sea Reefs (Scott, Seringapatam, Cartier, Hibernia - Australia)

The remote atoll reef of Scorr (14^oS; 121^oE) had extensive bleaching in May 1998. There was between 70% and 100% bleaching and mortality of corals between 1 m and 9 m, and 40% at 30 m depth. Sheltered shallow sites had up to 75% coral cover, which is now down to 15%, with more corals still dying 3 months after bleaching started. Some very large corals suffered several bleaching events and are now covered with patches of algae. Soft corals (Sarcophyton and Lobophyton) bleached, and some are disintegrating. Other remote reefs, Cartier and Seringapatam, were affected to a lesser extent. Corals on Hibernia were only slightly bleached.

(Clay Bryce, Luke Smith)

Tanzania

Corals bleached in mid-May 1998 along the whole coastline of Tanzania, from Mnazi Bay (10^oS – 15% to 25% of corals bleached) to Zanzibar (6^oS - bleaching between 25% and 50%) and Tanga (5^oS - about 25% of corals bleached). Acropora species bleached most with 80-95% in Chumbe, whereas about 40-70% of Acropora in other areas bleached. With Porites, some species bleached whereas others were unaffected. Survival after bleaching was about 50% in Mnazi Bay, and 60-80% in Bawe and Chumbe. Survival was very low (less than 40%) in Changuu and Chapwani. Water temperatures were 30.5^oC, about 2^oC above normal. Bleaching also coincided with much higher rainfalls than other years, and also when spring tidal ranges were about 4.5 m. By the end of October, 80-100 % of corals had died in Mafia Marine Park, which probably was the best coral reef in the country with almost 100% mixed coral community cover over vast areas. On Tutia Reef in the South, there is less than 5% coral still alive, with heavy mortality of Acropora, Porites, and Echinopora. In Chole Bay in the North, 100% of the Acropora were dead, and in the ‘coral gardens’ of Kinasi Pass, 80 to 90% of Acropora have died.

(Olof Linden, Chris Muhando, J.L. Solandt)

web@aims.gov.au
Last updated - 7 December 98

Copyright ©1996-1998 Australian Institute of Marine Science

URL http://www.aims.gov.au