The document summarizes a study monitoring the recovery of corals in Singapore that bleached during the 1998 global bleaching event. Surveys of coral reefs in June 1998 found 50-90% of corals were bleached. A monitoring program tagged 35 coral colonies over 10 surveys. Some corals recovered but others died. Recovery varied between genera. Chlorophyll levels increased over time. Sea surface temperatures in early 1998 were unusually high, likely causing the bleaching. Continued monitoring is needed to understand bleaching and aid coral reef recovery.

1. MONITORING THE
RECOVERY OF BLEACHED
CORALS IN SINGAPORE
FROM THE 1998 GLOBAL
MASS BLEACHING EVEN
EVENT
Karenne Tun
Chou Loke Ming
Jeffrey Low
Beverly Goh
Marine Biology Laboratory, Department of Biological Sciences
NUS

2. What are Corals and Coral Reefs?
CORALS
• Invertebrate
• Either hard or soft
• Each individual coral is called a polyp
• Solitary or colony forming
• Two basic types : hermatypic (harboring symbiotic algae)
ahermatypic (with no symbiotic algae)
CORAL REEFS
• Massive 3D geological entities, whose framework of limestone (calcium
carbonate) is made up of layers upon layers of coral skeleton
• Built entirely by reef-building corals (and other reef building organisms)

4. What is coral bleaching?
• Coral “bleaching” is defined as an unusual response of corals to most
stresses that are short of lethal.
• Corals turn pale or white!!!

5. Why do Corals Bleach?
• Corals thrive under very narrow tolerance ranges
• These include : temperatures too high or too low
salinity too high and too low
irradiance too high or too low
sediment loads too high
• Bleached corals may die if stress is sustained or worsened, but
can recover if stress is removed or lessened
• This can take a few days to over a year

6. 1998 - A Bleak Year for Coral Reefs
• Coral bleaching has been reported for nearly a century
• Prior to the 1980’s, all known cases were very limited in extent and
duration
• In the 1980’s, bleaching spread dramatically from very small areas
to huge areas of oceans
• 1998 also saw one of the largest El Niño’s in 150 years
• NOAA scientists (and many others too) have attributed mass bleaching
events over the past 1 1/2 decades to the rise in sea surface temperature
brought about by El Niño
• In 1998, a global mass bleaching of corals were reported in many
tropical countries

7. 1998 - A Bleak Year for Coral Reefs

8. Coral Bleaching in Singapore
• First ever observation of mass bleaching of corals in Singapore was
on 15nd June 1998 at the fringing reef along Pulau Hantu West
• Subsequent surveys to other reefs confirmed that the bleaching
was widespread, affecting all coral reefs in the Southern Islands of
Singapore
• Visual observations put the bleaching at between 50% to 90% at all
reefs surveyed
• Sea temperature readings have been observed to be increasing since
the second half of 1997, and unusually high sea temperatures were
observed in the coastal waters of Singapore since March 1998
• Reports from colleagues working in the region confirmed that the
bleaching was also widespread regionally

9. Monitor the Bleaching
• Initiated a monitoring programme to assess the recovery (if any) of the
bleached corals
• 3 permanent 10m line transects were established
• 35 coral colonies of various genera and growthforms were selected and
tagged
• Chlorophyll analysis were conducted
• Water temperature readings were taken during each survey
• Currently data is being analysed and results synthesized

10. Some Results
LINE INTERCENT TRANSECT
Benthos T1-1 T1-2 T1-3 T1-4 T1-5 T1-6 T1-7 T1-8
7/31/98 8/4/98 8/11/98 8/17/98 8/24/98 8/31/98 9/17/98 12/14/98
CB
CE 20-40 0-20 0-20 0-20 0-20
CF 80-100 60-80 60-80 80-100 0-20 0-20 0-20 0-20
CM 60-80 60-80 60-80 40-60 60-80 60-80 60-80 0-20
CMR
CS 20-40 20-40 0-20 0-20 0-20 0-20 0-20 0-20
Benthos T2-1 T2-2 T2-3 T2-4 T2-5 T2-6 T2-7 T2-8
7/31/98 8/4/98 8/11/98 8/17/98 8/24/98 8/31/98 9/17/98 12/14/98
CB
CE 80-100 80-100 80-100 80-100 80-100 0-20
CF 60-80 60-80 60-80 60-80 80-100 60-80 40-60 0-20
CM 20-40 20-40 40-60 20-40 20-40 20-40 20-40 0-20
CMR 80-100 80-100 20-40 0-20 0-20 0-20 0-20
CS 80-100 80-100 80-100 60-80 60-80 60-80 0-20
Benthos T3-1 T3-2 T3-3 T3-4 T3-5 T3-6 T3-7 T3-8
7/31/98 8/4/98 8/11/98 8/17/98 8/24/98 8/31/98 9/17/98 12/14/98
CB 40-60 20-40
CE 40-60 40-60 40-60 40-60 40-60 0-20 0-20 0-20
CF 60-80 60-80 60-80 20-40 20-40 0-20 0-20 0-20
CM 20-40 0-20 0-20 0-20 0-20 0-20 0-20 0-20
CMR 60-80 60-80 60-80 60-80 60-80 40-60 20-40 0-20
CS 40-60 40-60 40-60 40-60 40-60 20-40 0-20 0-20

11. Some Results
INDIVIDUAL COLONY MONITORING
• Outlines of the 35 colonies were digitally drawn from scanned
slides of the corals
• The percent bleaching of the corals and proportion of bleaching were
drawn onto the outlines, and a series of these outlines spanning the 10
surveys were produced
• Recovery was observed, but variable within and among coral genera
CHLOROPHYLL
• Chlorophyll concentrations at various wavelengths increased over 3
samplings

12. Some Results
• Colony status on 15 July 1998 (1st survey) and 14 Dec1998 (last survey) :
15 July 1998 14 Dec 1998
1,1 Pectinia 80-100% 0%
1,2 Pectinia 100% 0%
1,3 Pectinia 100% 0%
1,4 Pectinia 100% Colony dead
1,5 Pectinia 80% Colony dead
2,1 Goniopora 30-80% 0%
2,2 Goniopora 30-70% 0%
2,3 Goniopora 30-70% 0%
2,4 Goniopora 40-90% 0%
2,5 Goniopora 40-80% 0%
4,1 Euphylia 100% Colony dead
4,2 Euphylia 100% Colony dead
4,3 Euphylia 100% 0%, Part of colony dead
4,4 Euphylia 100% Almost entire colony dead
4,5 Euphylia 100% 0%

13. Some Results
• Recovery of the coral Pectinia sp. (Code 1,1) over several surveys
170898 240898
310898 171098

14. Some Results
• Some corals that didn’t survive :
• And some that did :

15. Some Results
TEMPERATURE
• 24 hour temperature data:
Date 24 hr Average Daytime Average Night- Daytime Night-time
Average Temp time Temp Max/Min Max/Min
27 Nov 1997 30.28 30.28 30.15 31.00-29.75 30.35-29.75
2 Dec 1997 30.49 30.58 30.40 32.40-30.20 30.60-30.00
9 Dec 1997 30.33 30.47 30.19 32.60-30.10 30.50-29.90
21 Jan 1998 30.04 30.44 30.10 31.70-30.00 30.50-29.70
5 Mar 1998 31.01 31.19 30.76 31.90-30.50 30.90-30.40
6 Mar 1998 33.89 33.98 33.77 34.55-26.55 34.30-32.95
13 Mar 1998 31.08 31.20 30.91 31.50-30.75 31.05-30.60
15 Mar 1998 31.04 31.13 30.91 31.55-30.65 31.05-30.65
16 Mar 1998 31.43 31.51 31.31 31.95-31.05 31.50-31.05
18 Mar 1998 31.33 31.43 31.22 31.85-30.95 31.40-30.60
3 June 1998 34.25 34.35 34.12 36.15-32.15 35.70-31.85
•Instantaneous sea surface temperature (SST) recordings :
Date (1998) 31 July 4 Aug 17 Aug 24 Aug
SST range 30.0-30.5 30.2-30.5 30.1-30.4 29.8-19.9

16. So What’s Next?
• It is important to study coral bleaching and their causes
• A relatively new science
• Numerous of organisations have already started focusing on the study
of bleaching and its causes
• Better access to SST in the coastal waters of Singapore
• More conscious of “natural” signals