1998 coral bleaching event in singapore

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

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)

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!!!

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

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

1998 - A Bleak Year for Coral Reefs

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

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

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

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

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%

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

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

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

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

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1998 coral bleaching event in singapore

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