bleaching

[RMurphy000 at aol.com]

August, 2000

Fiji Coral Bleaching Update from Ed Lovell and Richard Murphy,

Beginning in February 2000 hard and soft corals on some reefs in Fiji began 
bleaching. Bleaching continued and became more dramatic through March and 
April.  According to Al Strong's HotSpot data, there was a pool of warm water 
in the Fiji region during this time.  By mid July a few colonies where still 
bleached but most were either well on their way to recovery or had already 
died.  Colonies which did not survive are now colonised, or being colonised, 
by algae.  The only scars on the reefs are areas previously inhabited by 
Sinularia or Sarcophyton.

Ed surveyed reefs in southern Viti Levu, the largest island of Fiji, and 
Richard worked in Savusavu region on Vanua Levu, the 2nd largest Fijian 
island in an attempt to assess the consequences of this bleaching event.  On 
Savusavu reefs, by mid July, there were still a few colonies which were 
white, purple or yellow, but the bleaching had subsided with the cooler 
waters. At depths down to about 10 meters, some reefs appeared to have 
experienced 60 to 80 % hard and soft coral mortality.  Acroporids were among 
the hardest hit and the larger the colony, the greater the likelihood of it 
being killed.  Certain genera such as Diploastrea, Echinopora and Turbinaria 
seemed much more resistant. Some species (Pocillopora eydouxi and Acropora 
crateriformis) had minimal mortality.  Not all reefs were equally affected.  
Some, which previously had lower coral diversity and abundance, seem to have 
suffered less than those with greater diversity and % cover.  We did a few 
line transects at 33 meters and found much less mortality (7%-10%) with 
bleaching also reduced.

The bleaching/mortality event seems to have been patchy in Fiji.  The
highest mortality has occurred along the southern portion of Viti Levu and 
Vanua Levu.  Even within these areas of highest bleaching, the mortality has 
been variable. There appears to be a positive relationship between greater 
survivorship and areas of turbid waters, such as inshore reefs. Additionally, 
a Reef Check survey of the Great Sea Reef area north of Vanua Levu has 
determined minimal bleaching. This should be no surprise as NOAA's hotspot 
data showed the water to be cooler during the period when the temperatures 
were elevated to the south of the larger islands.  This large area of healthy 
coral, as well as deeper reefs, which were less affected, should bode well 
for a large recruitment to the areas of high mortality.

We have set up a number of permanent quadrats and transects and will continue 
to monitor them.  One thing of particular interest was the dramatic colour 
changes, which sometimes preceded bleaching. Some colonies of the genera 
Acropora and Montipora became a vivid purple, pink or yellow.  Likewise some 
Sinularia and Sarcophyton colonies 
became yellow or bleached to brilliant white. We would be interested to know 
if the pre-bleaching colours we describe have been observed by others who 
witnessed the development of bleaching events in the South Pacific and Indian 
Oceans.

Ed Lovell
Biological Consultants, Fiji
lovell at suva.is.com.fj

Richard Murphy
Ocean Futures Society
Rmurphy000 at aol.com