In contrast to alkaline conditions in oceans and many salt lakes,
ordinary freshwater tends to be somewhat acidic.  There's a lot of
natural variation (whether there's limestone around, whether there are
conifers contributing more acidic needles, etc.) in the pH, but often
conditions are acidic enough to be challenging for freshwater
mollusks, or even to prevent their survival in certain areas.
Increasing acidity, whether from rising carbon dioxide, acid rain,
decreasing salmon populations (which, by swimming up from the oceans
and then dying, historically had large impacts on the water chemistry
and nutrient loads in certain streams), changing vegetations, etc. is
having negative effects on freshwater mollusks.  Although the
variation in the oceans is not as wide as in freshwater, some parts of
the ocean naturally have lower pH and so will be more challenging to
build shells in than in other areas.

Many details of physiology would need to be worked out in order to
precisely predict the effects of increasing carbon dioxide on
mollusks.  How does the change in pH affect them generally?  Does the
average value or occasional extremes in variation have more of an
impact?  What direct effects are there on shell formation and
maintenance?  What effects are there on other organisms that interact
with them?  For example, greater impacts on top predators would leave
the mid-level predators more abundant, and these include a number of
the main mollusk-eaters.

In what testing has been done, some species seem unaffected, some seem
to do better, and some seem to do worse with high carbon dioxide
concentrations.  On average, more are harmed than helped, but a rapid
shift in the balance between organisms will produce more widespread
impacts than just whether an individual species has trouble calcifying
as the pH changes.

On Fri, Nov 23, 2012 at 3:51 PM, Fabio Moretzsohn <[log in to unmask]> wrote:
> It is a problem with terminology: the oceans are not currently acidic, so it
> is technically not correct to say they will become more acidic. The oceans
> are becoming less alkaline, i.e., the pH is lowering. Some people get too
> worked up about the terminology, while others flatly deny that the pH is
> lowering, or its cause (it may be more complex than simply more CO2 in the
> atmosphere).
>
> The point of the article is that the oceans pH is lowering due to more
> dissolution of carbon dioxide. While the pH is still above 7 and thus
> alkaline, there are concerns about the difference in pH causing problems for
> some organisms to secrete their calcium carbonate skeletons, like pteropods
> because they have very thin and highly soluble shells. However, I found the
> linked paper below reports the results of experiments with pteropods. The
> authors suggest that pteropods that naturally migrate into oxygen minimum
> zones may not be affect much by ocean acidification (at current conditions),
> although non-migratory species such as Diacria quadridentata, in the absence
> of acclimation and adaptation, could be significantly impacted. Organismal
> response to acidification is highly species-specific. Some mollusks may be
> able to change their metabolic response (to a certain degree) to compensate
> for lowering pH, but we don't know much (or anything in many cases) about
> the physiology of most species.
>
> Thanks for posting the link to the article, John.
>
> Maas, A. E., K. F. Wishner, and B. A. Seibel. 2012. The metabolic response
> of pteropods to acidification reflects natural CO2-exposure in oxygen
> minimum zones. Biogeosciences 9: 747-757.
> http://www.biogeosciences.net/9/747/2012/bg-9-747-2012.pdf
>
> Fabio M.
>
>
> On Fri, Nov 23, 2012 at 1:57 PM, Marien Faber <[log in to unmask]>
> wrote:
>>
>> And the comment by Phil Jones is not to be denied.
>>
>> Marien
>>
>> ________________________________
>> Date: Fri, 23 Nov 2012 12:11:15 -0500
>> From: [log in to unmask]
>> Subject: [CONCH-L] the changing environment
>> To: [log in to unmask]
>>
>>
>> For those interested in climate change and how it is affecting oceans and
>> molluscs, this audio piece is interesting.
>>
>> http://www.npr.org/2012/11/23/165749924/can-shellfish-adapt-to-more-acidic-water
>>
>> - John
>
>
>
>
> --
> -------------------------------------------------
> Fabio Moretzsohn, Ph.D.
> Assistant Research Scientist
> Harte Research Institute for Gulf of Mexico Studies
> Texas A&M University-Corpus Christi
> 6300 Ocean Drive, Unit 5869, Corpus Christi, TX 78412-5869
> Phone: (361) 825-3230; Fax: (361) 825-2050
> mollusca [at] gmail.com
> Managing Editor, American Malacological Bulletin
> Please consider the environment before printing this email.  Think Green!
>



--
Dr. David Campbell
Visiting Professor
Department of Natural Sciences
Gardner-Webb University
Boiling Springs NC 28017

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