Bleached Belizean Reefs

Tom Bright glover at
Wed Sep 16 16:22:06 EDT 1998

Memorandum To: Mr. James Azueta, Coordinator of Marine Protected Areas,
Belize Dept. of Fisheries.
From: Dr. Thomas J. Bright, Station Manager, Glover's Reef Marine Research
Station, Wildlife Conservation Society.
Subject: Wide scale Bleaching on all of Belize's Coral Reefs.
Date: Sept. 15, 1998

Dear James,

The entire Belizean coral reef ecosystem has experienced a massive and
pervasive event of coral bleaching. I have personally observed serious
bleaching down to a depth of at least 8 meters on the fore reef, top reef
and back reef of the main barrier reef at Ranguana Pass, the patch reefs at
Crawl Caye, Laughing Bird Caye, Scipio Caye, Bird Caye, pinnacle reefs
between Ranguana Pass and Lighthouse Caye off Placencia, and the shallow
water off Rum Point. Danny Wesby reports massive bleaching on the fore reef,
top reef, back reef and patch reefs at Glover's Reef Atoll down to at least
7 meters depth. Chris Berlin reports serious bleaching off Ambergris Caye.
Fishermen have told me of bleaching on the main Barrier Reef from Buttonwood
Caye to Ranguana Pass. Divers observed bleaching at South Water Caye and
Cocoplum Caye. All of the observers indicate that, although they have seen
bleaching in past years at this time, none have ever seen it so widespread
and so extensive as this year's event. They said that this is the warmest
they remember the water temperature ever being. All indicate that they began
noticing the bleaching during the last week or so.

>From this information I conclude that there has been a massive and
heretofore unprecedented (in the memory of those Belizean fishermen,
watermen and divers contacted) degree of zooxanthellae expulsion (bleaching)
in the reef coral populations of the entire Belizean Reef ecosystem from the
mainland beach out to the Atolls and including the main Belize Barrier Reef
down to at least 8 meters depth, and probably deeper. Further, it appears
that the bleaching is correlated in time with a period of exceptionally high
regional sea water temperature, and calm weather (there has been very little
wind during the last month). 

Bleaching at Crawl Caye on Sept. 2 was reported by me to Dylan Gomez and the
National Coral Reef Monitoring Group. Bleaching was noted on Sept. 7 at
Glover's Reef by the Wildlife Conservation Society staff. Since then the
bleaching has intensified and spread. Thus I conclude that the presumed
cause of the bleaching (high sea water temperature) manifested itself around
the first of September and has not yet abated. Further, I feel that the
bleaching started around the first of September, has progressed since then,
has not yet run it's course, and could get worse than it is now.

I observed water temperature, on my fish finder, at one meter depth, during
a sail from Belize City to Ranguana Pass and across the Gulf of Honduras to
Punta Sal, Honduras during the time in question. It was consistently between
30 C and 32 C and most of the time it was 31 C. Danny Wesby measured the
Glover's Reef Temperatures on Sept. 15. The surface temp. was 32 C and the
temperature at 2 meters was 30 C. The surface waters (upper 1/3 Meter or so)
on shoals and near cayes is warmer, often 36 to 38 C.

Some qualitative conclusions based on my personal observations are as
follows: Almost all Milleporan and Scleractinian corals and the Zooanthid
Palythoa exhibited some degree of bleaching. Total to high bleaching was
prevalent in Millepora, Agaricia, Porites porites and Palythoa. High to
moderate bleaching was prevalent in Montastrea, Siderastrea, and Diploria.
Moderate to low bleaching occurred in Dendrogyra and Acropora (although A.
palmata appeared only moderately bleached on the main Barrier Reef, totally
bleached colonies were observed in places on the lagoonal patch reefs). Most
Millepora, Porites porites, Agaricia and Palythoa were pure white . Many
Montastrea "annularis" (all three growth forms) were pure white over the
major part of their coralla, many were tan, all were affected. Other species
unnamed above were also affected. Black band disease was observed on M.
"annularis", Diploria and Gorgonia but not in any greater frequency than usual.

This is the most extensive case of bleaching that I have ever observed. I
hope that subsequent mortality is minimal. A monitoring effort should be
undertaken to assess the ultimate impact of this massive bleaching event on
the reef coral populations of Belize.

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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