Coral Bleaching

Tom Bright glover at
Mon Sep 7 12:45:48 EDT 1998

TO: Dylan Gomez, Chairman, Belize National Coral Reef Monitoring Committee
FROM: Thomas J. Bright, Station Manager, Glover's Reef Marine Research Station
SUBJECT: Random report, coral bleaching
DATE: Sept. 2, 1998

On Sept. 2, 1998, I was anchored at Crawl Caye at the north end of the
Victoria Channel ( 16 deg.35.89 min. N, 88 deg. 13.51 min. W). I snorkeled
on a patch reef just south of Crawl Caye and observed the following:
-About 85 % of the Montastrea annularis (knobby), down to a depth of 10 feet
or so, were severely "bleached", having a color approximately that of the
"almond" hue often used on kitchen appliances. Bleaching was also noticed on
-The water temperature in the upper foot or two of the water column was very
high, greater than my body temperature, and feeling like a hot bath.
-There was a sharp thermocline and below 3 feet depth the water temperature
was comparatively cool and "normal".
-The upper 6 inches of the water column was brown, an indication of a
phytoplankton bloom at the surface.
-There had been little wind for at least the previous 7 days (I have been
unable to sail my boat for that time and have been motoring- These are
called the "Calms of August"). This means wind forced mixing of surface
waters has been minimal, thus allowing overheating of the upper layer, and
thermal stratification.
-I suspect that the overheated upper layer can be a source of unusually high
temperature water which by some process may contact the corals on these
shallow  patch reefs down to 10 or more feet depth (some coral heads are
within 2 feet of the surface), thereby causing bleaching. Hypothetically, a
passing thunderstorm might cause vertical mixing??

This is a random observation of a stressful event on a lagoonal patch reef
in Belize. I don't know how widespread such occurrences are on these reefs
(you probably have more info.) but I suspect they are not uncommon. I wonder
if these shallow corals experience mortality following such a bleaching, or
do they regain their zooxanthellae and take it in stride. Considering their
importance as lobster habitat, I hope they are well adapted to occasional
bleaching episodes. 

Dr. Thomas J. Bright, Station Manager
Glover's Reef Marine Research Station
PO Box 2310
Belize City, Belize

Ph./Fax. 011-501-02-33855 (Belize City)
Ph. 011-501-05-22153 (Middle Caye)
E-mail <glover at>
Website <>

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