[Coral-List] Over fishing contributing to ocean acidification?

John Ware jware at erols.com
Thu Jan 22 08:56:43 EST 2009

Doug et al.

In the far distant past (1992) a paper appeared in Coral Reefs 
describing the process by which the deposition of CaCO3 by corals 
increases pCO2 in the water and decreases pH (increases acidity).

Ware, Smith, Reaka-Kudla:  Coral reefs: sources or sinks of atmospheric 
CO2?  Coral Reefs 11:127-130.

This was published at a time when some coral reef scientists were 
claiming that coral reefs were SINKS of CO2 - after all, look at all 
that CO3 stuff.  In fact, one reviewer, a geologist, questioned the 
utility of the paper because "everyone knows that the deposition of 
CaCO3 in water is a source of atmospheric CO2".


Douglas Fenner wrote:

>    I thought that the chemistry was that when corals secrete a skeleton,
>they put more CO2 into solution in the water, which actually makes the water
>more acid.  If fish solidify calcium carbonate, the same chemistry would
>have to apply, wouldn't it??  Would reverse as the calcium carbonate later
>dissolved.  But I'm no chemist.  (and I'm not defending overfishing!)   Doug
>----- Original Message ----- 
>From: "Gene Shinn" <eshinn at marine.usf.edu>
>To: <coral-list at coral.aoml.noaa.gov>
>Sent: Monday, January 19, 2009 4:48 AM
>Subject: [Coral-List] Over fishing contributing to ocean acidification?
>>An interesting article about an article published in Science. Gene
>>Fish an ally against climate change
>>    * New Scientist 13:02 16 January 2009 by Catherine Brahic
>>An unlikely ally may have been found in the fight against the effects
>>of climate change. Fish excretions seem to play a key role in
>>maintaining the ocean's delicate pH balance, says a study that also
>>reveals that there are 2 billion tonnes of fish in the world's oceans.
>>Bony fish excrete lumps of calcium carbonate, known as "gut rocks"
>>which are thought to dissolve in the upper layers of the ocean. A
>>team led by Rod Wilson of the University of Exeter in the UK has now
>>shown that the sheer amount of gut rocks produced plays a key role in
>>buffering the carbon dioxide that acidifies seawater.
>>"This study really is the first glimpse of the huge impact fish have
>>on our carbon cycle - and why we need them in the ocean," says
>>Wilson's colleague Villy Christensen of the University of British
>>Columbia in Canada.
>>Protective role
>>While marine biologists have known for some time that fish produce
>>gut rocks, until now no-one had estimated just how much calcium
>>carbonate is spewed out into the ocean in this way.
>>It was widely believed that most marine carbonate is provided by the
>>external skeletons of marine plankton. These microscopic organisms
>>are likely to be hard hit as climate change increases the acidity of
>>the oceans and their skeletons literally dissolve away.
>>The new study reveals that fish play an important role in stopping
>>this from happening.
>>ferent models to estimate the amount of fish biomass that is in the
>>global oceans, and its distribution.
>>By drinking salt water, fish ingest a lot of calcium, and they
>>excrete more or less calcium carbonate depending on their size and
>>the temperature of the water. "For a given total mass of fish,
>>smaller fish produce more than bigger fish, and fish at higher
>>temperatures produce more than fish at lower temperatures," explains
>>Surprise finding
>>The team then used data on how much carbonate fish produce on average
>>to calculate how much the fish biomass represented in their computer
>>models are likely to excrete.
>>This revealed that between 3% and 15% of all the calcium carbonate
>>produced in the oceans comes from fish. Wilson says this is a
>>conservative estimate - he and his team think the real figure could
>>be three times higher.
>>"I expect it will be a big surprise to most of the ocean scientists
>>who study the ocean carbon cycle," says Wilson. "Apart from a handful
>>of fish biologists around the world, the scientific community were
>>previously unaware that fish produce of any of this chalky mineral,
>>let alone enough to be significant on a global scale."
>>Eric Achterberg of the National Oceanography Centre in Southampton,
>>UK, says the study offers an insight into an underrepresented marine
>>process. "Whether the fish carbonate is really an important
>>contribution to the mid-water alkalinity is not certain yet and forms
>>an excellent topic of research," he says.
>>'Unrecognised allies'
>>Wilson agrees that it is not yet certain whether the gut rocks do
>>indeed dissolve in the upper layers of the ocean. Their chemical
>>structure suggests that they are very soluble in seawater and should
>>readily dissolve. But if future studies show this does not happen,
>>this will mean the gut rocks sink to the bottom of the ocean without
>>dissolving and buffering the oceans.
>>Because fish carbonate production goes up with temperature, fish are
>>likely to produce more carbonate - and be more effective buffers of
>>ocean acidity - as temperatures increase through global warming.
>>That's the good news. The bad news is that overfishing may have an
>>additional downside: in addition to depleting food stocks, it could
>>also deplete the precious carbonate buffer.
>>Because of the complexity of ocean chemistry, "we cannot really say
>>much with any confidence about how overfishing might affect ocean
>>acidification says Wilson. "But we definitely need to study this more
>>to help make better predictions about these future changes."
>>"We must buck the current trend of clear-cutting of the oceans and
>>foster these unrecognised allies against climate change," says
>>Journal reference: Science (DOI: 10.1126/science.1157972)
>>No Rocks, No Water, No Ecosystem (EAS)
>>------------------------------------ -----------------------------------
>>E. A. Shinn, Courtesy Professor
>>University of South Florida
>>Marine Science Center (room 204)
>>140 Seventh Avenue South
>>St. Petersburg, FL 33701
>><eshinn at marine.usf.edu>
>>Tel 727 553-1158---------------------------------- 
>>Coral-List mailing list
>>Coral-List at coral.aoml.noaa.gov
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>>12:11 PM
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