Paper discussion Fabry et al. 2008

Ocean Acidification

Repasado por Profa. Furumo

The Situation • Current atmospheric CO2 value is about

380ppmv compared to 280ppmv before the industrial age

• 1/3 of anthropogenic CO2 is absorbed by the seas

• Elevated partial pressure of carbon dioxide (pCO2) interferes with organisms ability to calcify structures and their metabolic physiology

Chemical Calisthenics

• Inorganic carbon system largely controls pH of seawater

• DIC (Dissolved Inorganic Carbon) exists in 3 primary forms, and at pH 8.2:

– 1) bicarbonate ion (HCO3-) – 88%

– 2) carbonate ion (CO32-) – 11%

– 3) aqueous carbon dioxide (CO2(aq)) – 0.5%

The Process • Calcium carbonate (CaCO3) is required by

calcifying organisms to make shells

• Increased CO2 = decreased [CO32-] & pH

• Increased CO2 yields fewer carbonate ions available to form CaCO3 through the reaction:

CO2 + CO32- + H2O = 2HCO3

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Does this effect all organisms equally?

• The CaCO3 saturation state (Ω) determines the extent to which organisms are affected

• Based on whether organism secretes shells in form of aragonite or calcite, 2 forms of CaCO3

• If Ωarag or Ωcal > 1, formation of shells favored

• If Ωarag or Ωcal < 1, dissolution is favored

• Importance of saturation states, ΩCaCO3 dictates calcification instead of pH

Aragonite

Saturation

Horizon (ASH)

Shoaling of Aragonite Saturation

Horizon

Danger Zones

• Temperature decrease = Increase in solubility of CaCO3

• Coupled with ASH migration

• Higher latitudes most vulnerable

• Pelagic organisms also at risk

• Coastal habitat uncertain due to

dynamic nature of circulation and eutrophication factors

Results of Acidification on Fauna

• Widespread ecological implications

• Decreased organism calcification capabilities

• Developmental complications

• Altered species distribution

• Change in diet/prey choices

• Physiological adaptations

Impact on Fauna

• Ecological Cascade beginning with plankton

• 3 primary CaCO3 producers

• Coccolithophores and Foraminifera = calcite excretion, produce majority of pelagic CaCO3

• Euthecosomatous pteropods = aragonite excretion, 50% more soluble in seawater

Pteropod C. pyramidata

• Habitat extends up to 55˚N

• Found at 400-500m depth during day and surface at night – Diel Vertical Migration

• Provide major source of CaCO3 to ocean interior & deep ocean, biological pump

• Shoaling ASH restricting its habitat distribution

• Will have to adapt to aragonite under-saturation or migrate to warmer, carbonate rich water

New Food Menu

• Gymnosomes prey exclusively

on shelled pteropods, so would

have to seek a new habitat in their absence

• Zooplankton and carnivorous fish (cod, haddock) that feed on pteropods would have to find new prey, such as juvenile fish

Pink salmon example

• Euthecosome L. helicina account for about 60% of juvenile pink salmon, before they switch to C. pyramidata in third year of life

• Models predict that a 10% decrease in pteropod production could result in a 20% drop in pink salmon body weight

Benthic organisms

• High commercial value (oysters, mussels)

• Most vulnerable during larval and early calcifying stages

– More soluble shell precursors

– Transient, unstable forms of CaCO3

– Ex) Amorphous CaCO3, high-magnesium calcite

Results of Acidification on Fauna

• Widespread ecological implications

• Decreased organism calcification capabilities

• Developmental complications

• Altered species distribution

• Change in diet/prey choices

• Physiological adaptations

Mechanisms in response to

hypercapnia

• Increased pCO2 diffuses into intra-/extra-cellular spaces, causing decrease in pH

• Methods to counteract internal acidification:

1) Passive buffering 2) Transport and exchange

of ions 3) Transport of CO2 in the

blood 4) Metabolic suppression

Physiological Adaptations

• Metabolism suppression – Short-term advantage,

long-term danger

– Shuts down expensive processes like protein synthesis

• Ex: Sipunculus nudus, a tidal worm, reduces metabolism under short-term CO2 elevation; over long-term (3-6 weeks), 100% mortality

Blood-Oxygen Binding

• Higher metabolic rates among organisms require more pH sensitive oxygen binding in the blood

• Epipelagic squid with high metabolisms could be impacted by increased CO2 present in the oceans as it interferes with O2 binding at the gills

Does anybody win?

• Tolerant fish – “fish mortality caused by anthropogenic CO2 is never expected in marine environments”

• Jellyfish frequency increase with pH decrease

• Will calcifying organisms eventually be replaced by non-calcifiers? i.e. Algae

Lets discuss

• What do you think the effects of acidification are on coastal environments?

• Which organisms (or which habitats) seem to be most at risk from ocean acidification?

• Can acidification occur in freshwater systems?

• What other possible solutions exists beyond simply reducing CO2?

• Is ocean acidification unavoidable given our daily habits?