1. IMPACTS OF POREWATER ACIDIFICATION ON RECRUITMENT & SIZE OF JUVENILE SOFT-SHELL CLAMS IN THE BAY OF FUNDY
Jeff C. Clements & H.L. Hunt
University of New Brunswick
Saint John, NB, Canada
ACCESS 2015, St. Andrews, NB

2. CO2 H+ CO2 H2O H2CO3 HCO3-1 CO3-2 Atmospheric Hydrogen ions Dissolved
Carbonic acid
Furthermore, with respect to behavioural impacts, most OA studies have focused on near-future open-ocean projections in the water column and have neglected sedimentary porewater conditions in coastal areas, which are often much more acidic than near-future projections (indeed coastal waters in general are often more acidic than near-future projections).
HCO3-1
CO3-2
Bicarbonate ions
Carbonate ions

3. CO2 H+ CO2 H2O H2CO3 HCO3-1 CO3-2 Atmospheric Hydrogen ions Dissolved
Carbonic acid
Furthermore, with respect to behavioural impacts, most OA studies have focused on near-future open-ocean projections in the water column and have neglected sedimentary porewater conditions in coastal areas, which are often much more acidic than near-future projections (indeed coastal waters in general are often more acidic than near-future projections).
HCO3-1
CO3-2
Bicarbonate ions
Carbonate ions

4. Biological effects of ocean acidification
PHYSIOLOGY
Calcification,
respiration,
growth & development,
reproduction,
pH balance
BEHAVIOUR
Predator avoidance & escape, prey selectivity & detection, olfaction, swimming, boldness, activity, anxiety, decision-making
OA impacts animals in two primary ways - physiologically and behaviourally – with observed effects appearing highly species specific.
These two broad biological effects can act independently or synergistically to impacts higher-level endpoints such as survival, fitness, and functioning at various levels of biological organization
Although behaviour plays a major role in survival, fitness, and ecological functioning, OA studies have primarily focused on physiology…
Survival
Fitness
Functioning (individual  ecosystem)

5. Implications M. mercenaria Settlers Increasing acidification
But a previous study has shown that more acidified porewater can impede the burrowing behaviour of newly-settled clams under still-water laboratory conditions.
However, this raises a number of questions:
First, given that the biological effects of near-future OA are highly species specific, how does this behaviour translate to other clam species in similar conditions?
Secondly, what happens to the animals if they’re exposed to water flow.
Finally, how does this translate to overall clam recruitment?
Increasing acidification

6. Implications M. arenaria Juveniles Increasing acidification
But a previous study has shown that more acidified porewater can impede the burrowing behaviour of newly-settled clams under still-water laboratory conditions.
However, this raises a number of questions:
First, given that the biological effects of near-future OA are highly species specific, how does this behaviour translate to other clam species in similar conditions?
Secondly, what happens to the animals if they’re exposed to water flow.
Finally, how does this translate to overall clam recruitment?
M. arenaria
Juveniles

7. Field study
Can porewater acidification affect juvenile soft-shell clam abundance & size in the Bay of Fundy?
Photo: A. Castillejos

8. 2012 field study Intertidal zone 4 sites 5 sample periods
LOW WATER MARK pH
60m
60m
60m
clams
Intertidal zone
4 sites
5 sample periods
HIGH WATER MARK

9. Back at the lab
CHEMICAL
BIOLOGICAL

10. Results: chemical
Sample period

11. Results: biological
Avg. pH

12. Results: biological Avg. pH Avg. shell length (mm) Avg. pH
Avg. # clams
Sample period
Sample period

13. Results: biological
Abundance

14. Growth and abundance patterns simply a function of time
Explanations
What we know
Growth and abundance patterns simply a function of time
Magnitude of growth and abundance a function of porewater pH/acidification
So what happens is that CO2 mixes with sea water and creates a weak acid – carbonic acid
Like all acids, this acid releases hydrogen ions into solution and leaves behind bicarbonate ions and, to a lesser extent, carbonate ions; some CO2 and carbonic acid left.
Leaves behind a complex brew of carbon compounds and ions.
H+ ions thus increase, resulting in a drop in pH (10fold increase in H+=drop of 1 pH unit).
It’s also important to keep in mind that CO2 also affects sedimentary pore water, which is already more acidic than overlying water
Furthermore, more pronounced in estuaries due to anthropogenic input of acidifying chemicals such as nitrogen, sulfur, and carbon.
These acidic conditions can reduce the carbonate saturation state of the water, hindering its ability to precipitate calcium carbonate.
As a result, acidic waters become corrosive to organisms with calcium carbonate shells, particularly in early life stages – and it’s important to note that this doesn’t just affect overlying water, but can enter sediments and affect pore water as well, which could have a substantial impact on infaunal organisms.

15. Explanations What we know If pH is a factor… Abundance data make sense
Size data appear counterintuitive
Black = protein synthesis
Gray = sodium, chloride, and ATPase activity
White = unaccounted ATP
Feeding = ability to allocate energy to compensate for OA effects

16. Acknowledgements Hunt-Rochette lab members
M.J. Maltais, A. McAslan, D. Scott, K. Cummings, A. Feicht, R. Rochette
M. Green, SJC Maine
Photo: H. Hunt
So what happens is that CO2 mixes with sea water and creates a weak acid – carbonic acid
Like all acids, this acid releases hydrogen ions into solution and leaves behind bicarbonate ions and, to a lesser extent, carbonate ions; some CO2 and carbonic acid left.
Leaves behind a complex brew of carbon compounds and ions.
H+ ions thus increase, resulting in a drop in pH (10fold increase in H+=drop of 1 pH unit).
It’s also important to keep in mind that CO2 also affects sedimentary pore water, which is already more acidic than overlying water
Furthermore, more pronounced in estuaries due to anthropogenic input of acidifying chemicals such as nitrogen, sulfur, and carbon.
These acidic conditions can reduce the carbonate saturation state of the water, hindering its ability to precipitate calcium carbonate.
As a result, acidic waters become corrosive to organisms with calcium carbonate shells, particularly in early life stages – and it’s important to note that this doesn’t just affect overlying water, but can enter sediments and affect pore water as well, which could have a substantial impact on infaunal organisms.

17. Twitter: @biolumiJEFFence
Thank you!
So what happens is that CO2 mixes with sea water and creates a weak acid – carbonic acid
Like all acids, this acid releases hydrogen ions into solution and leaves behind bicarbonate ions and, to a lesser extent, carbonate ions; some CO2 and carbonic acid left.
Leaves behind a complex brew of carbon compounds and ions.
H+ ions thus increase, resulting in a drop in pH (10fold increase in H+=drop of 1 pH unit).
It’s also important to keep in mind that CO2 also affects sedimentary pore water, which is already more acidic than overlying water
Furthermore, more pronounced in estuaries due to anthropogenic input of acidifying chemicals such as nitrogen, sulfur, and carbon.
These acidic conditions can reduce the carbonate saturation state of the water, hindering its ability to precipitate calcium carbonate.
As a result, acidic waters become corrosive to organisms with calcium carbonate shells, particularly in early life stages – and it’s important to note that this doesn’t just affect overlying water, but can enter sediments and affect pore water as well, which could have a substantial impact on infaunal organisms.
Questions?