climate change and coral reefs - the burning issues. guldberg_bleaching.pdf · climate change and...

Climate change and coral reefs - the burning issues.Climate change and coral reefs - the burning issues.

Ove Hoegh-GuldbergCentre for Marine Studies

The University of Queensland

Ove Hoegh-GuldbergCentre for Marine Studies

The University of Queensland

Beautiful CharismaticSocio-economically important100 million people

In serious declineSeries of human assaults (water quality, over-fishing, climate change etc)

Saudi ArabiaIndian Ocean IslandsFloridaPapua & New Guinea

Global Coral Reef Monitoring Network (2003)

Bellwood et al 2004 Nature 429: 827-833

Coral reefs are in rapid declineCoral reefs are in rapid decline

• Coastal development – Nutrients, toxins, and sediments

from agriculture and urban development

• Over-exploitation of marine species– Loss of critical functional groups

• Marine pollution– Sewage, petrochemicals, plastics

• Physical destruction– Tourism; destructive fishing

• Climate change– Rising sea temperatures, falling

alkalinities– Perceived by many as the primary

threat to coral reefs

• Coastal development – Nutrients, toxins, and sediments

from agriculture and urban development

• Over-exploitation of marine species– Loss of critical functional groups

• Marine pollution– Sewage, petrochemicals, plastics

• Physical destruction– Tourism; destructive fishing

• Climate change– Rising sea temperatures, falling

alkalinities– Perceived by many as the primary

threat to coral reefs

Even the Great Barrier Reef …

Climate change and coral reefsOutline:

Climate change and coral reefsOutline:

1. What are the changes that will affect coral reefs?

2. Coral responses: Coral bleaching and disease

3. Coral reefs over the next 20-50 years?

4. Socio-economic consequences

1. What are the changes that will affect coral reefs?

2. Coral responses: Coral bleaching and disease

3. Coral reefs over the next 20-50 years?

4. Socio-economic consequences

?

150

200

250

300

350

400

0 100000 200000 300000 400000Years before present

Car

bon

diox

ide

(ppm

v)

Present day

Tem

pera

ture

diff

eren

ce

from

pre

sent

day

(o C)

0

-3

-6

-9

3

6

Vostok Ice Core data

Temperature

Carbon Dioxide

600 ppm

Adapted from Falkowski et al (2000) Science 290: 291-296

740,00 years

375 ppmTODAY

2100

Pre-industrialLast 100 yearsNext 100 years

Changes that might affect coral reefs:Changes that might affect coral reefs:

• Storm frequency and intensity

• Precipitation, drought and land run-off

• Changing circulation• Sea level rise• Sea temperature• Carbonate alkalinity

• Storm frequency and intensity

• Precipitation, drought and land run-off

• Changing circulation• Sea level rise• Sea temperature• Carbonate alkalinity

Conditions under which Scleractinian reefs formConditions under which Scleractinian reefs form

Kleypas et al (1999)

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin

ity

Current tolerance limits

Today’s limit = 3.06

Today’s limit = 34oC

Marginalreef systems

Marginal reef systemsMarginal reef systems

Generally high latitudeAlkalinities of around 3.1

Low growthLeads to non-carbonate reef systems

Future conditions under a doubling of carbon dioxideFuture conditions under a doubling of carbon dioxide

Kleypas et al (1999)

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin

ity

Current tolerance limits

Future conditions:+3 degrees

60% of 2000 alkalinity

Today’s limit = 3.06

Today’s limit = 34oC

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin

ityCurrent tolerance limits



1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin




GENETIC CHANGE WITHIN POPULATIONi.e. EVOLUTION= a slow process

How are, or will, corals respond?How are, or will, corals respond?

Stress or disease

Dinoflagellate symbionts

0

20

40

60

80

100

0 20 40 60 80 100

Abs

orpt

ance

(%)

Symbiont density (%)

Normal seasonal variationBL

Local

Cold Warm

Low salinity

Toxins

High Light

Som

e ba

cter

ia

NB – problem of tissue necrosis in many diseases


Local

Local

RegionalGlobal

Local

Vibrio shiloi

Can cause bleaching (loss of Symbiodinium) to occur

Important distinctionImportant distinction

Bleached coralBleached coral Necrotic coralNecrotic coral

Polyps still present Dinoflagellates reduced

Can recover under mild Stresses …

Polyps dead, tissue falling off skeleton

Coral tissue deathVibrio coralyticusDifferent process to bleaching

LocalLocal

Local

RegionalGlobal

Local

Cold Warm

Low salinity

Toxins

High Light

Som

e ba

cter

ia



Hoegh-Guldberg and Fine (2004)

Saxby et al. (2003) Marine Ecology Progress Series 248: 85-97. Temperature below 14oC cause rapid bleaching of reef-building corals.

Saxby et al. (2003) Marine Ecology Progress Series 248: 85-97. Temperature below 14oC cause rapid bleaching of reef-building corals.

Temperature decreased to 9oC!

Bleached corals recovered after 6 months.

Higher plant literature:

Cold stress causes same physiological issues as hot stress

LocalLocal

Local

RegionalGlobal

Local

Cold Warm

Low salinity

Toxins

High Light

Som

e ba

cter

ia



Zooxanthellae are damaged and leave corals

Correlated with elevated sea temperatures.

Estimated loss of living coral colonies

from reefs in 1997-98:16% world wide.

Estimated loss of living coral colonies

from reefs in 1997-98:16% world wide.48%48%

1998

Mass coral bleaching caused by thermal stressMass coral bleaching caused by thermal stress• 95% correlation with increases in sea

temperature (1-2oC above long-term summer sea temperature maxima) and bleaching.

• Backed up experimentally• Basis for a highly predictive SST

program at NOAA (HotSpots):

• 95% correlation with increases in sea temperature (1-2oC above long-term summer sea temperature maxima) and bleaching.

• Backed up experimentally• Basis for a highly predictive SST

program at NOAA (HotSpots):

1998

2002

Strong, Hayes, Goreau, Causey and others

Threshold temperature – above which bleaching manifests itself (1-2oC above the long-term summer maximum temperatures

WHAT DOES THIS MEAN FOR CORAL REEFS?

Threshold temperature – above which bleaching manifests itself (1-2oC above the long-term summer maximum temperatures

WHAT DOES THIS MEAN FOR CORAL REEFS?

Hoegh-Guldberg (1999)

If sea temperature increases by as little as 1.5 degree above today’s temperatures, reefs will

bleaching every year. Sustainable?

If sea temperature increases by as little as 1.5 degree above today’s temperatures, reefs will

bleaching every year. Sustainable?

Hoegh-Guldberg (1999)

Coral Disease in the GBR

Recent surveys suggest significant increases in coral diseases in the GBR, particularly ‘white syndromes’(Willis et al. 2004)

Caribbean

Additional climate signal? Corals weakened by repeated stresses –greater susceptibility to the development of disease?

Outer shelf most affected?

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin




1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

1.0

2.0

3.0

4.0

5.0

10 15 20 25 30 35

Temperature(range)

Alk

alin




What about the change in alkalinity?

Is it changing?Is it changing?

• Hawaii Ocean Time Series • Hawaii Ocean Time Series

• Slope in Ω-arag = -0.022±0.08 y-1, 95% CI– C. Langdon, pers. comm.

• Calculate decrease over next 80 years– Decrease of -1.76– Takes average Ω-arag to 2.07

• Slope in Ω-arag = -0.022±0.08 y-1, 95% CI– C. Langdon, pers. comm.

• Calculate decrease over next 80 years– Decrease of -1.76– Takes average Ω-arag to 2.07

Source: Joanie Kleypas

The effect of temperature and CO2 on CO32-The effect of temperature and CO2 on CO32-

Sou

rce:

Joa

nie

Kle

ypas

Langdon et al. (2000)

Calcification ceases (even under high Ca2+)

Sou

rce:

Joa

nie

Kle

ypas

Pre-industrialpCO2 – 280 ppm

2060-69; pCO2 – 517 ppm

Assumption: Photosynthesis (the power house of calcification) increases linearly with temperature up to 2.7oC above today’s temperatures.

Is this so?

Net

pho

tosy

nthe

sis

(ug

O2.c

m-2

.h-1

)

-20

-15

-10

-5

0

5

10

15

20

25

1 2 3 428oC 30oC 32oC 34oC

Hoegh-Guldberg and Smith (1989)

+ 1oC

4 day exposure

Jones et al. (1998)

Temperature

0

5

10

15

20

25

30

35

40

25 27 29 31 33 35

Temperature

Cha

nge

(frac

tion)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

Ω-arag

Metabolic

Sum

Extremely marginal sat

Thermal stress

Marginal sat

No stress or land

Thermal stress & Extremely marginal sat

Increasing thermal stress

Increasing thermal stress

Loss of reef function and

services

Loss of reef function and

services

Reduced support to

subsistence usage

Reduced support to

subsistence usage

Reduced tourist value

Reduced tourist value Reduced

fish populations

Reduced fish

populations

Consequences?

Other? Coastal

protection

Other? Coastal

protection

High confidenceHigh confidence

Medium confidenceMedium confidence

Low confidenceLow confidence

Increased symbiotic

dysfunction & mortality

Increased symbiotic

dysfunction & mortality

CASE STUDY: Does it matter that the Great Barrier Reef may not be dominated by symbiotic corals in 30-50 years?

CASE STUDY: Does it matter that the Great Barrier Reef may not be dominated by symbiotic corals in 30-50 years?

Things to consider• More than $2 billion annual earnings from Reef

associated industries.• GBR has iconic attractiveness for visitors to

Australia generally – 83% of international visitors put the GBR first in what they associate with Australia.

• Coastal environment critical to the Australian lifestyle and wellbeing.

Things to consider• More than $2 billion annual earnings from Reef

associated industries.• GBR has iconic attractiveness for visitors to

Australia generally – 83% of international visitors put the GBR first in what they associate with Australia.

• Coastal environment critical to the Australian lifestyle and wellbeing.

Anecdotes from 1998: Tourism is flexible?

Population

0

5000

10000

15000

1990 2010 2030 2050 2070 2090Source: IPCC 2000

Mill

ion

A1F1 A1T A1B

A2 B1 B2

Figure 50: Six IPCC scenarios projected to 2100. The three variations of the A1 family are A1F1 (continued fossil fuel dominance), A1T (rapid transition to alternative energy sources), and A1B (balanced fuel mix). A1B is the marker scenario. The graph also depicts marker scenarios for the A2, B1 and B2 families.

GDP/GNP

0

200

400

600

1990 2010 2030 2050 2070 2090Source: IPCC 2000

$tril

lion

A1F1 A1T A1B

A2 B1 B2

GDP per head

$0

$20,000

$40,000

$60,000

$80,000

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100Source: IPCC 2000

A1F1 A1T A1BA2 B1 B2

CO2 emissions

0

5

10

15

20

25

30

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100Sour ce: IPCC 2000

GtC

A1F1 A1T A1B

A2 B1 B2

Population

0

5000

10000

15000

1990 2010 2030 2050 2070 2090Source: IPCC 2000

Mill

ion

A1F1 A1T A1B

A2 B1 B2

Figure 50: Six IPCC scenarios projected to 2100. The three variations of the A1 family are A1F1 (continued fossil fuel dominance), A1T (rapid transition to alternative energy sources), and A1B (balanced fuel mix). A1B is the marker scenario. The graph also depicts marker scenarios for the A2, B1 and B2 families.

GDP/GNP

0

200

400

600

1990 2010 2030 2050 2070 2090Source: IPCC 2000

$tril

lion

A1F1 A1T A1B

A2 B1 B2

GDP per head

$0

$20,000

$40,000

$60,000

$80,000

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100Source: IPCC 2000

A1F1 A1T A1BA2 B1 B2

CO2 emissions

0

5

10

15

20

25

30

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100Sour ce: IPCC 2000

GtC

A1F1 A1T A1B

A2 B1 B2

Global scenariosH

oegh

-Gul

dber

g an

d H

oegh

-Gul

dber

g (2

003)

394

335

107 54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500

Tropical North Queensland

Northern

Whitsundays

Mackay

Fitzroy

Wide Bay-Burnett

Thousand

persons

IntrastateInterstate

International

Figure 43: Estimated number of reef-interested visitors, 1999. The emphasis is

on ‘estimate’, based on categories derived from principal components analysis

of 1994-95 visitor statistics for Queensland (Pearce et al. 1997). This analysis

was valuable in identifying groups who prefer the type of holiday offered on the

Gold and Sunshine Coasts, and groups not interested in reef or national parks.

The allocation of the groups to fit the known total visitor patterns in 1999 was

also partly subjective.

Source: Derived from Pearce et

al. 1997, TQ 2002, OESR 2001

394

335

107 54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500


Northern

Whitsundays

Mackay

Fitzroy

Wide Bay-Burnett

Thousand

persons


International









al. 1997, TQ 2002, OESR 2001

394

335

107

54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500


Northern

Whitsundays

Mackay

FitzroyWide Bay-Burnett

Thousand persons

Intrastate Interstate International









al. 1997, TQ 2002, OESR 2001

394

335

107

54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500


Northern

Whitsundays

Mackay

FitzroyWide Bay-Burnett

Thousand persons

Intrastate Interstate International









al. 1997, TQ 2002, OESR 2001

394

335

107 54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500


Northern

Whitsundays

Mackay

Fitzroy

Wide Bay-Burnett

Thousand

persons


International









al. 1997, TQ 2002, OESR 2001

394

335

107 54

268

182

369

113

157

114

92

77

617

97

158

83

132

31

0

500

1,000

1,500


Northern

Whitsundays

Mackay

Fitzroy

Wide Bay-Burnett

Thousand

persons


International









al. 1997, TQ 2002, OESR 2001

5.6

8.0

4.5

3.5

0

2

4

6

8

10

A1 A2 B1 B2

Tota

l 19-

year

eco

nom

ic lo

ss ($

billi

on in

200

1 pr

ices

)

Figure 64: Total estimated economic loss according to the four scenarios over the first two decades of the 21st Century. Further losses will follow in subsequent decades which will increase the differences, as the annual loss accelerates in the A2 scenario indefinitely, and in A1 at least into the second half of the century. Annual losses will grow at a decreasing rate in the B1 and B2 scenarios, and may stabilise from mid-century. Discounted at 5% pa, the four values become $2.9, 4.3, 2.4 and 1.9 billion, respectively (for 19 years only, without any residual value calculation). The chart shows industry losses only; there is no attempt to value ecosystem services and other indirect and future use, or any bequest and other non-use functions of the World Heritage Area.

5.6

8.0

4.5

3.5

0

2

4

6

8

10

A1 A2 B1 B2

Tota

l 19-

year

eco

nom

ic lo

ss ($

billi

on in

200

1 pr

ices

)

Figure 64: Total estimated economic loss according to the four scenarios over the first two decades of the 21st Century. Further losses will follow in subsequent decades which will increase the differences, as the annual loss accelerates in the A2 scenario indefinitely, and in A1 at least into the second half of the century. Annual losses will grow at a decreasing rate in the B1 and B2 scenarios, and may stabilise from mid-century. Discounted at 5% pa, the four values become $2.9, 4.3, 2.4 and 1.9 billion, respectively (for 19 years only, without any residual value calculation). The chart shows industry losses only; there is no attempt to value ecosystem services and other indirect and future use, or any bequest and other non-use functions of the World Heritage Area.

WWF: Socio-economic implications for climate change for Australia’s Great Barrier Reef (2003)

ConclusionsConclusions

1. Bleaching is a sign of stress – triggered at local scales by a range of phenomena including cold, low salinity and some bacterial infections.

2. At global scales, mass bleaching is triggered by small increases in sea temperature (no other variable has been associated with this trend in global stress).

3. Increased temperature and reduced carbonate alkalinity of seawater will largely eliminate coral dominated ecosystems.

4. In the next 20-30 years, coral bleaching will increase and coral growth will continue to decrease.

5. Socio-economic consequences are expected to be considerable and reduce the ability of coral reefs to support humans and their industries

1. Bleaching is a sign of stress – triggered at local scales by a range of phenomena including cold, low salinity and some bacterial infections.

2. At global scales, mass bleaching is triggered by small increases in sea temperature (no other variable has been associated with this trend in global stress).

3. Increased temperature and reduced carbonate alkalinity of seawater will largely eliminate coral dominated ecosystems.

4. In the next 20-30 years, coral bleaching will increase and coral growth will continue to decrease.

5. Socio-economic consequences are expected to be considerable and reduce the ability of coral reefs to support humans and their industries

climate change and coral reefs - the burning issues. guldberg_bleaching.pdf · climate change and...

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