[Coral-List] Coral Bleaching in Thailand

james true jaydeetee1 at gmail.com
Tue May 18 23:25:54 EDT 2010

Dear Listers

Over the past month, bleaching of hard and soft corals has been observed on
both sides of the Thai peninsula (i.e., Andaman Sea and Gulf of Thailand).
The bleaching is the worst that has been reported since the 1998 bleaching,
but differs significantly in that, during the 1998 event, the Andaman Sea
reefs were essentially unaffected. The bleaching corresponds to an
unusually protracted period of calm weather, significantly elevated sea
surface temperatures around offshore islands and a slight tardiness in the
onset of normal monsoon rainfall and wind conditions.  Bleaching appears to
be less severe in those localities where rainfall has occurred.

On the Andaman side, extensive bleaching has been reported at offshore
locations in the northern Surin Islands (which are the southernmost of the
Mergui chain extending into Myanmar) and in the Tarutao/ Adung-Rawi complex
in the far south (adjacent to northwest Sumatra).  Bleaching has not been
reported in the Similan Islands, which are subject to seasonal upwelling
from the current SW monsoon.  The bleaching in the Andaman reefs includes
all major families, although faviids, agariciids and pocilloporids appear to
be strongly affected; acroporids, poritids and mussids appear slightly less
vulnerable to bleaching under current conditions. Acroporas appear not to be
the most severely affected group, except for table and corymbose species;
branching Acroporas are frequently bleached only on their upper surface.

On the Gulf side, bleaching has been reported at Koh Tao (offshore), and at
inshore islands in Chumphon and Prachuap provinces.  Shallow reefs around
Koh Tao are 40-60% bleached; affected groups include pocilloporids,
agariciids, poritids and other symbiotic orgainsms such as giant clams.
Acroporas are affected as for the Andaman description.  Correspondents on
Koh Tao also report a significant surge in diseases affecting corals,
especially a "patch lesion" affecting Porites.  Bleaching in Prachuap varies
strongly with location: shallow reefs (such as Koh Singha) are 60-70%
bleached, mostly in shallow (<2m) locations; slightly deeper reefs
(4-6m) around Koh Talu are only ~10% bleached - mostly amongst the
agariciids and fungiids.

Bleaching in the east coast reefs of the Gulf of Thailand (towards Cambodia)
is variable, but appear to average ~40% bleached.  Affected corals in Rayong
Province are as described for Prachuap.  Reefs in Chantaburi Province
(further east from Rayong) are reported to also exhibit extensive bleaching
in soft corals, with 100% bleaching of Sarcophyton reported.

No bleaching has been reported for the Inner Gulf region (Chonburi
Data loggers record that water temperatures at Koh Tao were elevated for
most of April, peaking at ~34 degrees C in early May.  Some minor bleaching
of the upper surfaces of branching Acropora was noticed during the faviid
spawning event in early April, when water temperatures were ~32 degrees C.
No significant rainfall has occurred there this calendar year, and
conditions have been generally very calm.  Sea surface temperatures did not
exhibit the usual "winter" low this year, and seem to have peaked much
earlier than "normal" years ... by way of contrast, the 1998 SST peak did
not occur until the end of May at Koh Tao.  Water temperatures recorded by
loggers around Koh Mun (Rayong province) were likewise elevated, with
temperatures above 33 degrees C for a large proportion of April and early

- James
Dr James True
Center for Biodiversity in Peninsular Thailand
Faculty of Science, Prince of Songkla University
Hat Yai, Thailand

Tel: (+66) 2235 3062
Mob: (+66) 89 002 4490
Email: jaydeetee1 at gmail.com

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