Coral bleaching Thailand
edcolijn at bart.nl
Wed Jul 1 12:57:13 EDT 1998
Bangkok Post [Two Articles]
June 29, 1998
Worst ever coral bleaching in Thai seas
Sea temperature rise puts coral at risk
The warming of sea water has caused widespread coral bleaching in the
Gulf of Thailand from Trat province in the eastern coast down to
Singapore, according to Chulalongkorn University's marine science expert
He described the phenomenon as the worst ever to occur but stopped short
of putting the blame on El Nino.
Dr Suraphol said coral bleaching was detected in April in almost every
part of the gulf especially tourist attractions such as Chang, Tao and
Pha-ngan islands. Fortunately however, he said this had not yet occurred
in the Andaman Sea.
Coincidentally, he noted that the same phenomenon was also detected in
the Great Barrier Reefs in Australia and in Singaporean waters.
He disclosed that the temperature of water in the gulf had increased
significantly from an average of 28-29 degrees Celsius to 32 degrees. He
said it could be possible that the warming of the sea water was caused
by the El Nino weather phenomenon.
The bleaching is caused by the escape of a kind of algae called
zooxanthellae from the coral structure as a result of sea water warming.
Eventually, this can lead to the death of the coral. Also affected by
sea water warming is giant clam or hoi mue sua.
Dr Suraphol said it was as yet too soon to predict whether the affected
corals would survive or not. Normally, he said it would take at least
2-3 years for the bleached corals to start to recover slowly unless the
problem is further compounded by sea pollution.
The immediate impact of coral bleaching is a drop in the number of
tourists who are interested in diving or snorkelling with the long-term
impacts yet to be determined, said the scientist, adding that the death
of corals would result in more serious shore erosion as corals serve as
a natural barrier to waves.
Dr Suraphol's concern about coral bleaching confirms the alarm raised by
some diving instructors who earlier observed the phenomenon in the sea
off Pattaya, near Samaesan and Koh Samet island.
Dave Chandler, in his letter to the Bangkok Post, said he suspected sea
water warming as the culprit but did not rule out pollution from
industrial sites and discharges from tankers and vessels.
The Pattaya-based diving instructor said both soft and hard corals had
died, leaving only bleached white limestone. Nevertheless, he said other
corals look healthy and unaffected.
Mr Chandler said his diving computer measured sea temperature at 33
degrees Celsius in shallow water and 32 degrees at depths below 6-8
metres. Normally, the temperature would be no more than 30 degrees, he
He expressed concern that if the corals were wiped out, it would deal a
tremendous blow to the ecology of the gulf and would seriously threaten
Thailand's badly-needed income from tourists who come here to dive.
More than a little off colour
MARINE LIFE: Scientists have discovered many of Thailand's coral
reefs are not looking very healthy. In some places 100 percent of the
most common Acropora coral has been bleached white Dr Suraphol Sudara
and Dr Thammasak Yeemin of the Coral and Seagrass Research Unit,
A healthy coral reef is a dynamic world of vivid colour thanks to the
single-cell algae called zooxanthellae. This algae, which lives in the
cells of the coral, shares a symbiotic - or mutually advantageous -
relationship with the coral.
The zooxanthellae provides the coral not just with colour, but also
extra food through the process of photosynthesis. In return, the coral
gives the algae a home and protection inside its skeletal structure.
Things normally go well between the two partners until something
disrupts their symbiotic relationship, resulting in the coral host
kicking out its algal roommate.
The sad fact is in most cases, coral cannot survive on its own - without
zooxanthellae it bleaches white and gradually dies. The even sadder fact
is, this is happening now in the Gulf of Thailand.
Since the 1980s marine biologists around the world have been concerned
about coral bleaching, and although they could see it happening in many
places, scientists were having a hard time confirming what was actually
causing this disastrous phenomenon.
Even today, there is no conclusive evidence about why bleaching actually
Coral bleaching has occurred in the Caribbean, the Pacific and Indian
Oceans, and in the Arabian Gulf and Red Sea.
Bleaching was first noticed in Thai waters in 1979 on a few patches of
coral off Phuket. By 1991 the problem was widely recognised on the
Andaman side of the kingdom. It was not really observed in the Gulf of
Thailand until recently.
Then in late April, the bleaching of coral in the Gulf was widely
noticed at islands off the coast of Chumpon and Surat Thani.
Then it was discovered areas on the east coast such as Rayong, Trat and
the inner part of the Gulf around Ko Sichang and Pattaya were also
But the phenomenon was quite strange. While some species in the coral
colonies were affected by bleaching, others were maintaining their
A preliminary survey at Ko Rum Ra offshore from Bangsapan, Prachuab Kiri
khan province, where bleaching was noticed at the end of April is
continuing to this day.
The situation there seems serious as the reef appears in parts to be
completely white. About 10 species of the Acropora group - which
includes staghorn coral and table coral - had suffered almost 100
percent bleaching; Pocillopora damicornis is about 80 percent bleached
and the other 20 percent is pale in colour; about 60-70
percent of massive coral in the Porites group were found to be
bleached, especially the coral lying in shallow flat parts of the reef.
Coral in the shallower water appears to have been more effected by the
bleaching than that in deeper water, and the sea water temperature in
shallower areas was found to be rather high, around 32-33 degrees
The reefs around Koh Tao, a popular island for divers and snorkelers has
also fallen victim to bleaching which was observed there in early May,
when the recorded sea water temperature also proved to be high - about
31-32 degrees Celsius.
The most significant impact appears to be on the Acropora group of hard
corals - the most commonly found coral in this region - which was
completely bleached white. More than 80 percent of another hard coral
Pocillopa damicornis was found to be bleached.
Fungia were also all found to be bleached and even some species of
colourful soft coral had turned white. It appears the bleached soft
coral might not be able recover.
Similar bleaching incidents were recognised at coral communities on the
inner part of the Gulf starting from Ko Sichang through to Pattaya to
Sathaheep. A survey also showed bleaching extended further along the
east coast of the Gulf of Thailand to Trat.
The extent of the bleaching and the long-term damage it causes to the
reef remains to be seen. The death of particular species - particularly
the Acropora group - appears to be extensive.
While it might be possible for the coral to recover from the effects of
bleaching, the problems it faces do not end there.
If the coral is overrun by filamentous algae, or if other alien
invertibrates make their homes on its skeleton, rejuvenation of the
coral might be hampered or indeed made impossible.
Some groups of coral might recover, such as Galaxea, Platygyra and
Lobophyllia, but the question of how long the recovery process could
take remains a mystery. As is understanding how great the impact will be
on the reproductive cycle or fecundity of the effected reef organisms.
Neither is it known what the long term impact of bleaching will be on
other reef organisms such as sea urchins and reef fish. Or whether the
bleaching will increase the rates of bio-erosion on the reef. All these
issues still need to be studied.
The cause of the unusually high sea water temperatures all over the Gulf
of Thailand remains to be proved by physical oceanographers, however it
has been suggested it is linked to the El Nino weather phenomenon. Even
though El Nino is more or less over, this bleaching might be part of its
© Copyright The Post Publishing Public Co., Ltd. 1998
edcolijn at bart.nl
The Indonesian Nature Conservation Database
More information about the Coral-list-old