Climate change impacts on reef algae
Guillermo Diaz-Pulido
Centre for Marine Studies &
ARC Centre of Excellence for Coral Reef Studies,
The University of Queensland, Australia
g.diazpulido@uq.edu.au
&
Universidad del Magdalena, Colombia
All photos by G. Diaz-Pulido (unless noted)
1
Outline
•
•
•
•
Background
Climate change factors
Impacts of Warming
Impacts of CO2 & Ocean acidification
– Macroalgae
– Coral-algal interactions
• General Conclusions
2
Background
• Key ecological roles
– Roles in reef degradation & phase shifts
3
Warming-induced coral bleaching
and algal increase
GBRMPA
Warming causes coral bleaching.
Widespread colonization after coral mortality
4
Warming-induced coral bleaching
and algal increase
Benthic Algae
Corals
Diaz-Pulido & McCook, 2002
Diaz-Pulido & McCook 2002
5
Increased coral bleaching
Frequency
Diaz-Pulido & McCook, 2002
Hoegh-Guldberg, 1999
•Coral bleaching  ↑ frequency & intensity
6
Warming-induced coral bleaching
and algal increase
Coral bleaching
Coral mortality
Algal colonisation
Future reefs
dominated by algae !
?
7
Coral reefsClimate
ecosystemschange
and climate change
• Anthropogenic climate change
• Caused increase in CO2 levels
– Emissions from fossil fuels
– Emissions from aerosols
– Cement manufacture
– Deforestation
8
9
CO2 levels
Geological eviden: 20 mya
10
CO2 levels
390
370
350
330
310
11
Lough, 2009
CO2 levels: IPCC
Yr: 2100:
900 ppm
12
Meehl et al. 2007, IPCC
CO2 levels: Recent models
Year 2100: >1000ppm
13
Meinshausen et al. 2009. Nature, 458: 1158-1162, 30 Apr
Global warming: IPCC
Due to  greenhouse [gas]
Yr: 2100:
4o C
To  0.74 oC
last century
14
Meehl et al. 2007, IPCC
Global warming: Recent models
Yr: 2100:
5-7 oC
Year 2100: up 5-7 oC
15
Meinshausen et al. 2009. Nature, 458: 1158-1162
Climate change
• Increase CO2 & temperatures will cause:
Climate stressor
Exposure
Sea level to rise
2100: 310 mm higher
than today
Precipitation patterns Variable trends
Ocean circulation
patterns
Tropical Storms
Least studied aspect:
changes in currents,
upwelling
Decreased frequency
16
Storms
Oouchi et al 2006
17
18
2007
Vulnerability of macroalgae to
climate change
19
Vulnerability of macroalgae to
climate change
Ocean
circulation
Storms
Uv
CO2
Rainfall
ToC
Space
availability
Sea
level
20
Diaz-Pulido et al, 2007. GBRMPA
Effects of Increased Temperature on
Macroalgae
21
Temperature
Relative growth rate / day
• Effects :
Cladophoropsis
–  photosynthesis
–  growth
• Wide range of tolerance
– 8 to 35oC (Pakker et al 1995)
– Many unable to survive >33oC
Microdictyon boergesenii
22
Pakker et al 1995, J. Phycol 31: 499-527
Temperature
Relative growth rate / day
• Effects :
Dictyopteris justii
–  photosynthesis
–  growth
• Wide range of tolerance
– 8 to 35oC (Pakker et al 1995)
– Many unable to survive >33oC
• Narrow physiological thresholds
Coelothrix irregularis
23
Pakker et al 1995, J. Phycol 31: 499-527
Temperature
• Effects :
–  photosynthesis
–  growth
Great Barrier Reef
Chlorodesmis
Caulerpa
• Wide range of tolerance
– 8 to 35oC (Pakker et al 1995)
– Many unable to survive >33oC
• Narrow physiological thresholds
Halimeda
Photosynthetic
rates
24
Effects of warming on seaweed
photosynthesis
Thresholds
Halimeda opuntia
• Variable thresholds
• Can be narrow in many
tropical algae
Relative O2 evolution
120
100
80
60
40
20
0
30
31
32
33
34
Temperature (oC)
35
36
37
38
25
Diaz-Pulido et al in prep.
Temperature
• Effects :
Seasonal Dynamics of Dictyota
–  photosynthesis
–  growth
40
Cover (%)
• Wide range of tolerance
– 8 to 35oC (Pakker et al 1995)
– Many unable to survive >33oC
Upwelling
23oC
Upwelling
23oC
50
• Narrow physiological thresholds
• Distribution ranges
• Alter seasonality
30
Rainy
>28oC
20
10
0
Apr
Jun
D. bartayresiana
Aug
Oct
D. pfaffii
Dec
Feb
D. pinnatifida
26
Diaz-Pulido & Garzón-Ferreira, 2002. Bot. Mar. 45:284-292
Temperature
Fleshy Macroalgae
–  photosynthesis
–  growth
• Wide range of tolerance
30
% Cover
• Effects :
18,1
20
10
3,7
0,8
0
– 8 to 35oC (Pakker et al 1995)
– Many unable to survive >33oC
Dictyota spp. Length
• Narrow physiological thresholds
• Changes in seasonality &
distribution ranges
150
–  temperature   Cover &
algal growth
– Small To Δ: Δ seasonality
-50
98,4
113,14
% Growth
100
50
0
-100
-100
21-23°C
24-26°C
27-29°C
Temperature treatments
D. Cuesta 2009
27
Effects of warming on macroalgae
Key knowledge gaps
• Adaptive capacity to cope with increased SST
• Identify vulnerable species to global warming
• Changes in latitudinal distributions
• Effects of  temperature on temperature-controlled life
cycles (not understood)
• Shifts in competitive ability (e.g. turfs more competitive
than fleshy algae)
28
Effects of Increased CO2 on
Macroalgae
29
Increased CO2 & Ocean
acidification
CO2   Carbonic Acid  pH = Ocean acidification
25%
H2CO3
30
Hoegh-Guldberg et al. 2007. Science 318:1737-1742
Increased CO2 & Ocean
acidification
 CO2  ↑ growth of fleshy
seaweeds
 pH   calcification
31
Meehl et al. 2007, IPCC
Impacts of increased CO2
on fleshy seaweeds
Gracilaria
1200 ppm
• Effects on fleshy algae:
650 ppm
–  photosynthesis
–  growth, eg algae with
no CCM
Control
Gao et al., 1993. J. Appl. Phycol. 5:563
Days
• Very limited data for
tropical species
Growth rate (C)
Lomentaria articulata
Kubbler et al 1999. Plant, Cell & Environment 22: 1302-1310
32
Impacts of increased CO2
on fleshy seaweeds
33
Primary Productivity: Respirometry
Respirometry chambers
Growth: Δ Weight
34
Impacts of increased CO2
on fleshy seaweeds
Photosynthesis
CO2 levels
Control (Today)
Medium (500 ppm)
High (780 ppm)
Macroalgae
•Small responses of algae to increased [CO2 ]
•Large variability in photosynthetic responses between taxa
•Minor to no apparent response (2 taxa)
•Bell shape response:  in medium, but  in high [CO2] (4 species)
•Increased with increasing CO2 (2 spp)
•Decreased with increasing CO2 (1 spp)
35
Diaz-Pulido et al in prep.
Impacts of increased CO2
on calcareous algae
Aragonite saturation
• Reduced saturation state of
aragonite and calcite
• Effects:
ppm CO2
–  calcification of red coralline
algae
–  Primary production
–  Recruitment
–  mortality, dissolution
36
Hoegh-Guldberg et al. 2007. Science 318:1737-1742
or CCA
37
Hoegh-Guldberg et al. 2007. Science 318:1737-1742
Impacts of increased CO2
on coralline algae
38
Impacts of increased CO2
on calcareous algae
Porolithon onkodes
4
Temperature
Low (25 oC)
High (28 oC)
% Weight increase / month
3
2
Skeleton
dissolution
1
0
n=15
-1
To exacerbates
CO2 impacts
-2
-3
Control
Medium
High
39
[CO2]
Anthony, Kline, Diaz-Pulido. 2008. PNAS 106:17442-17446
Net Productivity (umol O2 / cm2 / d)
Porolithon onkodes
Temperature
Low (25 oC)
High (28 oC)
Control
Medium
High
40
CO2
Anthony, Kline, Diaz-Pulido. 2008. PNAS 106:17442-17446
CO2-dosing and temperature control experiment
pH
T
(C)
8.00 -8.40
25 - 26
TA
(mmol
kg-1)
2375 - 2450
pCO2
(matm)
HCO3
(mmol
kg-1)
CO3
(mmol
kg-1)
High-Mg
calcite
135 - 460
1390 - 1930
207 - 415
1.2-2.3
130 - 465
1325 - 1885
225 – 440
1.3-2.5
520 - 705
1900 - 2050
155 - 200
0.8-1.1
520 - 705
1860 - 2020
170 - 220
0.9- 1.2
1010 - 1350
2080 - 2210
95 - 125
0.5-0.7
1020– 1360
2020 - 2190
105 - 135
0.6-0.8
Control
28 - 29
7.85 -7.95
25 - 26
2375 - 2450
2050
28 - 29
7.60 -7.70
25 – 26
2375 - 2450
2090
28 - 29
Saturation state of High-Magnesium calcite: <1 = Under saturated
Carbon parameters were estimated using the program CO2SYS.
The saturation state of calcite assume a concentration of 14 Mole % MgCO3
41
Impacts of increased CO2
on calcareous algae
Kuffner et al 2007
42
Impacts of increased CO2
on calcareous algae
• Reduced saturation state of
aragonite and calcite
• Effects:
Ambient [CO2]
High [CO2]
–  calcification of red coralline
algae
–  Primary production
–  Recruitment
–  mortality, dissolution
•
Shifts in spp. dominance
– Calcifying  non-calcifying algae
– Loss of corallines:  settlement
cues for coral larvae
Kuffner et al. 2008. Nature Geoscience
43
Impacts of increased CO2:
Shifts in dominance
44
Hall-Spencer et al. 2008. Nature 454:96-99
Impacts of increased CO2:
Shifts in dominance
Shore
Volcanic CO2 vents
Caulerpa,
Cladophora,
Asparagopsis,
Dictyota,
Sargassum
45
Hall-Spencer et al. 2008. Nature 454:96-99
Impacts of increased CO2:
Shifts in dominance
46
Effects of increased CO2 on fleshy &
calcareous algae
Key knowledge gaps
• Adaptive capacity to cope with  CO2 and  pH
– Potential adaptation by secreting less soluble skeletons
– CCA radiated during Eocene World was warmer and had higher CO2
 Adaptation?
• Identify vulnerable species, related to CCM
• Effects on reproduction, competitive ability (eg CCA  fleshy
algae)
• Decline in CCA and follow on effects on coral recruitment
47
Coral – Algal Interactions
48
Coral-algal competition &
Ocean acidification
• Coral-algal competition is a
critical process in reef
ecology
• No information on the
effects of  CO2 on coral –
algal interactions
•
Current experiments in the Great
Barrier Reef
49
Coral – algal competition &
Ocean acidification
Key knowledge gaps
• Explore variability in competitive outcomes
– Vulnerable coral & Algal spp.
• Mechanisms of competition
– Chemical
– Microbial, etc
• Interactive effects of temperature & CO2
• Roles of herbivory & nutrients on interactions under
high CO2
50
Conclusions
• High diversity of taxa & groups  large variability in
responses
• Variety of ecological roles  impacts on reefs would be
variable
– Effects on reef primary productivity
– Reef construction, sediment production
– Critical effects on coral settlement
• Will algae be the winners?
– Reef macroalgae are at least as vulnerable to ocean acidification and
global warming as are corals
– Future reefs might not be dominated by fleshy seaweeds
– Winners (? red algae) & losers (coralline algae)
51
??
52