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 <K.FABRICIUS@email.aims.gov.au>
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