Increasing light availability
caused by reductions in sea ice
triggers macroalgae regime
shifts in the Arctic
Kim Scherrer, Susanne Kortsch, Øystein Varpe, Gesa Weyhenmeyer,
Bjørn Gulliksen, Raul Primicerio
31/01/2017
Arctic Frontiers 2017
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Background
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• Climate warming
pronounced in the
Arctic
• Increasing water
temperature
• Prolonged ice-free
season  Light
regime
• Impacts on arctic
ecosystems
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© Ingrid Onarheim/
Bjerknes Centre for Climate Research
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• Community shifts in Kongsfjord and
Smeerenburgfjord
• Macroalgae expand at expense of red
calcareous algae
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Kortsch et al. (2012)
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Which mechanisms caused the shifts?
Aim
to unravel how climate-driven changes in
temperature and light, via their effects on
algal growth and competition, can explain
regime shifts in polar benthos
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Method
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Model
Algae dominance
under temperature,
light and
competition
scenarios
αMC
gC
dC
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-
αCM
gM
dM
Crowley et al. 2005
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Temperature
+/-
+
gC
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C
Calcareous
algae
Macroalgae
gM
Mp
Phycodrys Rubens
Md
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Light
gC
Calcareous
algae
Macroalgae
gM
Clark et al. 2013
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Key results
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Scenarios
αCM > αMC
αCM = αMC
αCM < αMC
0°C
5°C
10°C
CxM
CxM
CxM
C&Mp
CxMd
CxM
MpxC
MdxC
CxM
MpxC
MdxC
MpxC
MdxC
CxM
MpxC
MdxC
CxM
MpxC
MdxC
CǀMd
MPxC
CǀMp
CxMd
MpxC
MdxC
CxM
MpxC
MdxC
Temperature and competition secondary
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Light crucial for macroalgal dominance
If C are good
competitors
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• Expansion of macroalgae as growth rate increases
• Threshold effect
• Small increase in gM switches algae dominance
• Temperature does not favor macroalgae
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Discussion
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• What causes
macroalgae
shifts?
• Non-linear light
increase
• Light causes large
growth rate
increase
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Conclusions and implications
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• Light increase due to decreased sea ice most
likely cause for macroalgae regime shifts
• Temperature effects secondary
•
•
•
•
Reversal possible, but unlikely
Shifts expected in similar ecosystems
Altered carbon cycling and biodiversity
Further studies urgent due to rapid rate of sea
ice retreat
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References
• Kortsch et al., 2012. "Climate-driven regime
shifts in Arctic marine benthos." Proc. Natl.
Acad. Sci. 109
• Crowley et al., 2005. "A general model of
local competition for space." Ecol. Lett. 8
• Clark et al., 2013. "Light-driven tipping
points in polar ecosystems". Glob. Change
Biol. 19
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Thank you!
Photo: Bjørn Gulliksen
Kim Scherrer
[email protected]
Universitat Autònoma de Barcelona
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Model
• Area cover of C and M
1. Growth rate (g)
2. Competition coefficient (α)
3. Death rate (d)
• Initial area cover
𝑑𝑑𝑑𝑑
𝑑𝑑𝑑𝑑
𝑑𝑑𝑑𝑑
𝑑𝑑𝑑𝑑
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= 𝒈𝒈𝑪𝑪 𝐶𝐶𝐶𝐶 + 𝑀𝑀𝑀𝑀(𝜶𝜶𝑪𝑪𝑪𝑪 𝒈𝒈𝑪𝑪 − 𝜶𝜶𝑴𝑴𝑴𝑴 𝒈𝒈𝑴𝑴 ) − 𝒅𝒅𝑪𝑪 𝐶𝐶
eq. 1
= 𝒈𝒈𝑴𝑴 𝑀𝑀𝑀𝑀 + 𝑀𝑀𝑀𝑀(𝜶𝜶𝑴𝑴𝑴𝑴 𝒈𝒈𝑴𝑴 − 𝜶𝜶𝑪𝑪𝑪𝑪 𝒈𝒈𝑪𝑪 ) − 𝒅𝒅𝑴𝑴 𝑀𝑀 eq. 2
(Crowley et al., 2005)
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Light conditions
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Results
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