TWO REPORTS GBR BLEACHING Date: Wed, 1 Apr 1998 14:04:22 GMT From: anya@emu.usyd.edu.au (Anya Salih) Subject: re: Bleaching on GBR Between 1-14 March, I was able to join one of the GBRMPA crown-of-thorn starfish survey cruises to GBR mid-shelf reefs, between Cairns and Innisfail. At each visited reef I made video and coral spp cover/ bleaching-condition transects, which I'm now analyzing. Briefly, the coral bleaching situation on these reefs was as follows: - Seawater temperatures (taken in 7-15 m of water at backreef moorings) was 27C to 30C, and mostly 30C throughout the day. - A variable degree of bleaching was recorded on all reefs; was most pronounced in shallower water, on reef flats and reef tops (1-3m depth); and extended to 15m and possibly deeper. The degree of bleaching (complete vs partial) and the numbers of spp affected, sharply declined with depth. At shallow depths almost all corals had some degree of bleaching and many were completely bleached. Deeper (below 2m depth), bleaching was more pronounced on unshaded coral surfaces while undersides of branches and other shaded colony parts were still pigmented. This indicates that solar radiation such as high PAR (and possibly PAR+UV or UV) played a role in this mass bleaching episode. - Bleaching was generally less severe in front-reef rather than back-reef zones. - The degree of bleaching on the 5 surveyed reefs (in a line approx 100 km) was variable: 1.The northern-most reef surveyed, Elford Reef (at approx. 35km from shore), was moderately bleached, with most corals showing partial rather than full bleaching; 2.Coates Reef, in the middle of that line of reefs (and about 43 km from Mulgrave and Russel Rivers) was the most affected, with approximately 90% bleaching on reef tops and reef edges; and 60-70% on upper slope in backreef areas and approx. 70% bleaching of reef top corals in reef-front areas. 3. Hedley Reef, close to Coates reef (and approx 50km from mainland), less than 60% bleaching. 4. About 30 km south and approx. 42km from the mainland, Cayley Reef was severely bleached on reef tops to 3m depth (approx. 80% of corals partially or fully bleached) and less severely bleached on slopes, with many Pocillopora damicornis and Porites bommies remaining unbleached. 5. Feather Reef, (about 33 km from Johnstone River) - mostly only partial bleaching of corals in shallower depths and only a few spp with complete bleaching (P. damicornis and S. hystrix); and relatively little bleaching on slopes. - Some rough estimates of bleaching susceptibilities of some spp: P. damicornis, S. hystrix and S. pistillata were the most affected species, (70-100% fully bleached); less so, but also strongly bleached (60-90%) were tabular (A. hyacinthus group) and digital (A. humulis group) acroporiids; faviids were 50-90% bleached in shallow reef areas and less than 40% on slopes; massive Porites were only partially bleached, with many unbleached, while approx. 70% of encrusting poritiids (P.lichen, P. annae) were fully bleached; very fleshy corals were least affected, e.g. Symphyllia spp less than 5% bleached. - Bleaching appeared to be induced by combined effects of elevated temperature and solar radiation. Low salinity, caused by heavy rainfalls a few weeks prior to the onset of bleaching, may have contributed to stress, particularly on inner-shore reefs, but seems unlikely to be the main cause of bleaching on mid-shelf reefs. Anya Salih Internet: anya@emu.usyd.edu.au Marine Physiology Lab Telephone:02-93513006 (Zool) Zoology AO8 02-93517540 (EMU) School of Biological Sciences Facsimile:02-93517682 The University of Sydney Sydney, 2006, AUSTRALIA Date: Thu, 02 Apr 1998 11:09:00 +1000 From: KATHARINA FABRICIUS Subject: extensive bleaching of soft corals on near-shore reefs of the GBR Soft corals have experienced extensive bleaching on the near-shore reefs of the central Great Barrier Reef. Affected are almost all zooxanthellate orders and families (Briareum is one exception), but the taxa show varying degree of susceptibility. Many near-shore areas are 100% bleached within the upper 5 m, and ~ 20% bleaching is still observed at 8 - 12 m depth. The rate of mortality is high even among otherwise very persistant alcyonacean taxa (such as Sinularia). We are about to conduct a 2-weeks AIMS survey to determine the extent of bleaching on the central GBR, as well as species-specific and habitat-specific susceptibility in soft corals to bleaching. Results should be available in a month time. Katharina Fabricius Australian Institute of Marine Science (AIMS), CRC for the Ecologically Sustainable Development of the Great Barrier Reef Postal address: AIMS, PMB No 3, Townsville MC Qld 4810, Australia Fax: (+ 61) 7 47725852, Phone: (+61) 7 47534412 Email: k.fabricius@email.aims.gov.au Web: http://www.gbrmpa.gov.au/~crcreef/4news/Exploring/feat18.html