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What is ocean acidification?

A reduction in ocean pH due to the uptake of anthropogenic CO2


What is the current state of ocean acidification?

Currently 30% higher than any time in the last 650,000 years


What is aragonite?

It is a carbonate mineral that makes up bony and shell structures in marine creatures


How will ocean acidification affect organisms possessing aragonite shells?

Negative aragonite saturation associated with decreased ocean pH - if aragonite saturation goes below 100%, these organisms may start to dissolve


What is the distribution of aragonite?

It is found in greater amounts near the equator, and in lesser amounts in the poles.
If aragonite saturation continues to decrease, organisms in the poles will be most greatly affected


How do increasing CO2 concentrations in the ocean affect organisms with aragonite shells?

CO2 reacts with H2O to produce bicarbonate (HCO3) and hydrogen (H), which makes the ocean mare acidic.
The hydrogen ions naturally react with carbonate ions producing (HCO3)
There is therefore less carbonate for marine organisms to convert into calcium carbonate, and the calcium carbonate can even dissociate producing more carbonate ions to react with the hydrogen
Organisms must use more energy (ATP) to produce calcium carbonate in a more acidic ocean


Results of ocean acidification on individual marine organisms

-Thinner, smaller, weaker shells in shellfish (especially in larval stages which have very thin shells)
-Lower survival due to increased crushing and drilling by predators
-Lower survival due to increased risk of desiccation
-Reduced fertilisation of gametes in coral due to deformed flagellum in sperm that impacts their swimming - lower population growth?
-Reduced hearing ability in clown fish larvae due to deformed morphology of CaCO3 otoliths or disruption of acid-base balance in neuro-sensory system - higher predation


Example of experience influencing pH sensitivity

Lewis et al. 2013
Two Arctic copepods
Calanus: diurnal vertical migration
Oithona: non-migratory
Calanus experiences greater pH range than Oithona due to the vertical migration
The impact from acidification is greater on the non-migratory zooplankton
Possibly due to increased energetic costs of maintaining physiological processes in lower pH


What organisms does ocean acidification benefit?

Non-calcifying marine algae - more dissolved CO2 for increased photosynthesis and growth


What is the community structure of volcanic CO2 vents in the Mediterranean which are acidic water?

Dominated by marine organisms that do not have CaCO3 hard parts such as non-calcifying algae


Tropical ocean predictions under acidic conditions

-Corals will become increasingly rare
-Algae will become more abundant
-Biodiversity will decline


Interspecific interactions in an increasingly acidic ocean

Predators that eat shelled prey may decline in numbers e.g. pink salmon and pteropods - as pteropod populations decline, it will lead to a decline in pink salmon body weight and reduce the population size/viability


What pteropod species was tested in water with the projected pH of the ocean in 2100?

Limacina helicina
Shell dissolved completely in a month and a half
Bednaršek et al. 2014


What are the 4 options marine species have in response to ocean acidification?

1. Tolerate
2. Adapt
3. Move
4. Local extirpation or total extinction


Example of tolerating ocean acidification

Organisms must acclimatise and change phenotype in response to OA
Eg. urchin eggs have an acid-protecting jelly coating, so may be able to make more of this, although there may be indirect energy costs


How might organisms adapt to tolerate ocean acidification?

-Species need fast generation time relative to pH change
-Current rate of ocean acidification is 100 times faster than in the last 10 million years
-Standing genetic variation required, or a novel mutation. Some species have the genetic diversity, for example on the coast of California there is a lot of natural variation in pH


What test was carried out on a Coccolithophore?

Emiliania huxleyi
Reared for 500 generations in 3 CO2 scenarios
Then placed into an assay to measure growth rate of the population and PIC production (particulate inorganic carbon)
Those given a chance to evolve performed better
Lohbeck et al. 2012


Option of moving away from ocean acidification to non-OA water

Larger animals can swim and larvae can drift away, but they must stay within physiological limits


Might ocean acidification cause local extirpation or extinction?

Two most recent mass extinctions associated with high CO2 so it is very possible


What can society do to reduce the effects of ocean acidification?

-Freshwater and acidic soils lead to lower ocean pH
-Mitigate run-off and erosion
-Reduced carbon emissions
-Riparian buffers, wetlands
-Conserve natural pH buffering of coastal soils
-Return crushed old shells
-Need network of sensors to monitor pH dynamics of ocean