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
-
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?
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