Physiologically relevant bleaching
threshold methods provide updated
global coral bleaching predictions
Cheryl Logan, California State University, Monterey Bay
John Dunne, NOAA-GFDL
Mark Eakin, NOAA Coral Reef Watch
Simon Donner, University of British Columbia
Coral Reefs: A Vital Ecosystem
Economic Benefits
Ecological Benefits
• Structural habitat
• High biodiversity
Jim Raymont, James McVey
• Commercial fishing
• Tourism
• Coastline
protection
• Natural products
Coral
Coral Reef
ReefBleaching
Bleaching
What is it?
Corals expel the symbiotic
algae that provide them
energy (and color)
Healthy Coral
Bleached Coral
Causes/ Threats
Temperature Stress
Solar irradiance
Water flow
Acidification
Sedimentation
GBRMPA
•
•
•
•
•
NOAA Coral Reef Watch Program
• Continuous monitoring of satellite SSTs at
global reef scales
• Provide researchers and stakeholders
information about when bleaching is likely
• Prediction tools lead to appropriate
management decisions and design of global
climate policy
CRW Coral Bleaching Prediction Method:
SST (°C)
Anomalies above the mean maximum monthly
climatology (MMM) are summed over 12 weeks
32
31
30
29
28
anomaly
anomaly
MMM
climatology
1
2
3
4
5
Week
Glynn and D'Croz 1990; Liu et al. 2003
Degree Heating Week (DHW) =
Anomalyweek1+ Anomalyweek2 + … +
Anomalyweek12
DHW > 4 = bleaching likely
DHW > 8 = mortality likely
Glynn and D'Croz 1990; Liu et al. 2003
Applied to monthly data:
Degree Heating Month (DHM) =
Anomalymonth1+ Anomalymonth2 + Anomalymonth3
DHM > 1 = bleaching likely
DHM > 2 = mortality likely
Donner et al. 2005
Test bleaching prediction method
against Reefbase observations
1. Coral Reef Watch Current Method (Control)
2. Variability Based Method
- McClanahan et al. 2007, Oliver & Palumbi 2011, Boylan & Kleypas 2008, Teneva et al. 2011, Donner 2011
3. Modified Climatology (MMMmax)
- Donner et al. 2009, Teneva et al. 2011, Donner 2011
4. Variability + MMMmax
- Donner 2011
Ground-truth CRW Method with Reefbase
Observations between 1985-2010
Prediction Method
1° x 1° - monthly
MMM + Control
MMM + Variability
MMMmax + Control
MMMmax + Variability
0.5° x 0.5° - monthly
MMM + Control
MMM + Variability
MMMmax + Control
MMMmax + Variability
4km2 - monthly
MMM + Control
MMM + Variability
MMMmax + Control
MMMmax + Variability
0.5° x 0.5° - biweekly
MMM + Control
MMM + Variability
MMMmax + Control
MMMmax + Variability
Global DHM
Bleaching Alert
Level
1.0
1.0
0.7
0.7
Bleaching
Frequency
(% Global
Reefs / Year)
10.0
10.0
10.0
10.0
% Predicted
but not
Observed
(alpha)
8.0
8.1
8.1
8.2
% Observed
but not
Predicted
(beta)
69.0
71.6
64.9
65.2
Predictive
Power (%)
31.0
28.4
35.1
34.8
1.6
1.6
1.0
0.9
10.0
10.0
10.0
10.0
8.2
8.0
8.3
8.2
64.1
71.3
56.8
58.1
35.9
28.7
43.2
41.9
2.1
1.5
1.0
1.0
DHW
7.7
11.0
5.6
8.5
10.0
10.0
10.0
10.0
8.6
8.5
8.9
8.8
73.2
75.3
63.4
63.6
26.8
24.7
36.6
36.4
10.0
10.0
10.0
10.0
8.4
8.3
8.5
8.4
65.1
73.2
61.6
66.1
34.9
26.8
38.4
33.9
Logan et al. 2012, ICRS Proceedings
New IPCC class global climate models:
Earth System Models (ESMs)
GFDL Earth System Model 2M
(1/3° grid, monthly SST output)
IPCC 5th Assessment future scenarios:
4 Representative Concentration Pathways (RCPs)
8.5 W/m2: Heavy emissions
6.0 W/m2: Moderate emissions
4.5 W/m2: Active mitigation
3.0 W/m2: Aggressive mitigation
20
0
00
80
60
40
20
0
80
Future Bleaching under Climate Change:
Mitigation Scenarios
60
40
20
1960
%
80
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events e
40
80
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events e
60
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events e
80
0
1960 2000
1980 2020
2000 2040
2020 2060
2040 2080
2060
1980
2080
60
40
20
0
60
40
20
1960
0
19602000
19802020
20002040
20202060
20402080
2060
1980
2080
% Global Reefs Bleaching >2x every 5yrs
ESM2M
rcp26: MMMmax
ESM2M rcp26:
MMMmax
+ Control + Control
100
80
3.0 W/m22
60
40
20
1960
0
1960 2000
1980 2020
2000 2040
2020 2060
2040 2080
2060
1980
Year
Climatological
period
2080
100
80
60
40
20
0
ESM2M
rcp45: +MMMmax
ESM2M rcp45:
MMMmax
Control + Control
100
4.5 W/m2
1960
80Active
Mitigation
60
40
20
0
19602000
19802020
20002040
20202060
20402080
2060
1980
Year
2080
0
0
0
0
0
0
0
0
80
Future Bleaching under Climate Change:
Emissions Scenarios
60
40
20
0
1960
%
80
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events
0
80
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events
0
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events
0
1960 2000
1980 2020
2000 2040
2020 2060
2040 2080
2060
1980
2080
60
40
20
0
1960
60
40
20
0
19602000
19802020
20002040
202020602040
1980
20802060
2080
% Global Reefs Bleaching >2x every 5yrs
ESM2M
rcp60: MMMmax
ESM2M rcp60:
MMMmax
+ Control + Control
100
80
6.5 W/m2
60
40
20
1960
0
1960 2000
1980 2020
2000 2040
2020 2060
2040 2080
2060
1980
Year
2080
100
80
60
40
20
0
ESM2M
rcp85:+MMMmax
ESM2M rcp85:
MMMmax
Control + Control
100
8.080W/m2
1960
60
40
20
0
19602000
19802020
20002040
202020602040
1980
20802060
Year
2080
Adapt or acclimatize?
I. Thermal tolerance varies with
thermal history
•
•
Physiological acclimatization
Directional selection
e.g., Hughes et al. 2003
II. Thermal tolerance transiently
increases after bleaching
•
•
Symbiont reshuffling
Directional selection
e.g., LaJeunesse et al. 2009
Could these “adaptive”
mechanisms keep pace
with climate change?
I. Thermal tolerance varies with thermal history
% Global Reefs
Bleaching >2x every 5yrs
ESM2M rcp60 rolling climatologies
100
20 yr
40 yr
60 yr
80 yr
100 yr
% reefs with >2 bleaching events every 5 yrs
90
%
80
70
6.5 W/m2
60
50
40
30
20
10
0
1960
1980
2000
2020
Year
2040
2060
2080
II. Thermal tolerance transiently increases after bleaching
100
% Global Reefs
Bleaching
>2x every 5yrs
ESM2M rcp60
symbiont reshuffling
% reefs with >2 bleaching events every 5 yrs
90
%
80
70
no adjust
2 yr return
5 yr return
10 yr return
6.5 W/m2
60
50
40
30
20
10
0
1960
1980
2000
2020
Year
2040
2060
2080
A transient increase in thermal tolerance after
a bleaching event only moderately delays
severe bleaching by 2100
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events every 5 yrs
20
0
1960
1980
% reefs with >2 bleaching events every 5 yrs
≈
ç
2000
2020
2040
2060
2080
ESM2M rcp26: MMMmax + Control
100
80
60
40
20
0
1960
1980
90
80
2000
2020
2040
2060
2080
ESM2M rcp60 rolling climatologies
100
20 yr
40 yr
60 yr
80 yr
100 yr
ō
70
60
50
40
30
20
10
0
1960
1980
2000
90
80
2020
2040
2060
2080
ESM2M rcp60 symbiont reshuffling
100
% reefs with >2 bleaching events every 5 yrs
•
If corals can “adapt” to their recent thermal
history over the previous 40-60 years, severe
bleaching could be prevented in over half of
global reefs by 2100
40
ō
•
Without acclimatization or adaptation, only
the “aggressive mitigation” RCP scenario
predicts < 100% of reefs undergoing high
frequency bleaching by 2100
60
ō
•
80
ō
Conclusions
ESM2G rcp26: MMMmax + Control
100
no adjust
2 yr return
5 yr return
10 yr return
70
60
50
40
30
20
10
0
1960
1980
2000
2020
2040
2060
2080
A transient increase in thermal tolerance after
a bleaching event only moderately delays
severe bleaching by 2100
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events every 5 yrs
20
0
1960
1980
% reefs with >2 bleaching events every 5 yrs
≈
ç
2000
2020
2040
2060
2080
ESM2M rcp26: MMMmax + Control
100
80
60
40
20
0
1960
1980
90
80
2000
2020
2040
2060
2080
ESM2M rcp60 rolling climatologies
100
20 yr
40 yr
60 yr
80 yr
100 yr
ō
70
60
50
40
30
20
10
0
1960
1980
2000
90
80
2020
2040
2060
2080
ESM2M rcp60 symbiont reshuffling
100
% reefs with >2 bleaching events every 5 yrs
•
If corals can “adapt” to their recent thermal
history over the previous 40-60 years, severe
bleaching could be prevented in over half of
global reefs by 2100
40
ō
•
Without acclimatization or adaptation, only
the “aggressive mitigation” RCP scenario
predicts < 100% of reefs undergoing high
frequency bleaching by 2100
60
ō
•
80
ō
Conclusions
ESM2G rcp26: MMMmax + Control
100
no adjust
2 yr return
5 yr return
10 yr return
70
60
50
40
30
20
10
0
1960
1980
2000
2020
2040
2060
2080
A transient increase in thermal tolerance after
a bleaching event only moderately delays
severe bleaching by 20-30 years
% reefs with >2 bleaching events every 5 yrs % reefs with >2 bleaching events every 5 yrs
20
0
1960
1980
% reefs with >2 bleaching events every 5 yrs
≈
ç
2000
2020
2040
2060
2080
ESM2M rcp26: MMMmax + Control
100
80
60
40
20
0
1960
1980
90
80
2000
2020
2040
2060
2080
ESM2M rcp60 rolling climatologies
100
20 yr
40 yr
60 yr
80 yr
100 yr
ō
70
60
50
40
30
20
10
0
1960
1980
2000
90
80
2020
2040
2060
2080
ESM2M rcp60 symbiont reshuffling
100
% reefs with >2 bleaching events every 5 yrs
•
If corals can “adapt” to their recent thermal
history over the previous 40-60 years, severe
bleaching could be prevented in over half of
global reefs by 2100
40
ō
•
Without acclimatization or adaptation, only
the “aggressive mitigation” RCP scenario
predicts < 100% of reefs undergoing high
frequency bleaching by 2100
60
ō
•
80
ō
Conclusions
ESM2G rcp26: MMMmax + Control
100
no adjust
2 yr return
5 yr return
10 yr return
70
60
50
40
30
20
10
0
1960
1980
2000
2020
2040
2060
2080
Acknowledgements
GFDL Climate Ecosystem Modeling Group
Kenneth Casey (NOAA NODC)
Tess Brandon (NOAA NODC)
Jianke Li (NOAA Coral Reef Watch)
Gang Liu (NOAA Coral Reef Watch)
Joanie Kleypas (NCAR)
Lida Teneva (Stanford)
Salvador Jorgensen (Stanford)