Geochimica et Cosmochimica Acta 67: 1129-1143, by Thresher et al. Their data clearly suggest, as they describe it, that "a change in carbonate saturation horizons per se as a result of ocean acidification is likely to have only a slight effect on most of the live deep-sea biogenic calcifiers," which is a most reassuring result.
Thresher, R.E., Tilbrook, B., Fallon, S., Wilson, N.C. and Adkins, J.
2011. Effects of chronic low carbonate saturation levels on the
distribution, growth and skeletal chemistry of deep-sea corals and other
seamount megabenthos. Marine Ecology Progress Series 442: 87-99.
The authors state that ocean acidification results from a net uptake of CO2
emissions that causes a decrease in the carbonate ion concentration of
the ocean, which has been "forecast to hamper production of biogenic
carbonates (aragonite and calcite) in the skeletons, shells and tests of
marine taxa (Orr et al., 2005; Moy et al., 2009),"
thereby "threatening their long-term viability and severely impacting
marine ecosystems." They go on to note, however, that these predictions
"are based primarily on modeling studies and short-term laboratory
exposure to low-carbonate conditions," citing Riegl et al. (2009), Veron et al. (2009) and Ries et al.
(2010). And they say that "their relevance to long-term exposure in
the field and the potential for ecological or evolutionary adjustment
are uncertain," citing Maynard et al. (2008).
What was learned
The five researchers report that they "found little evidence that
carbonate under-saturation to at least -30% affected the distribution,
skeletal composition, or growth rates of corals and other megabenthos on
Tasmanian seamounts." In fact, they found that "both solitary
scleractinian corals and colonial gorgonians were abundant at depths
well below their respective saturation horizons and appeared healthy,"
while HMC echinoderms were common to as deep as they sampled (4011 m),
in water that was approximately 45% under-saturated. They also report
that "for both anthozoan and non-anthozoan taxa, there was no obvious
difference in species' maximum observed depths as a function of skeletal
mineralogy." In other words, the community "was not obviously shifted
towards taxa with either less soluble or no skeletal structure at
increasing depth." And in light of these observations, they write that
"it is not obvious from our data that carbonate saturation state and
skeletal mineralogy have any effect on species' depth distributions to
the maximum depth sampled," and they say that they also saw "little
evidence of an effect of carbonate under-saturation on growth rates and
Commenting further on their findings, Thresher et al. write
that "the observation that the distributions of deep-sea corals are not
constrained by carbonate levels below saturation is broadly supported by
the literature," noting that "solitary scleractinians have been
reported as deep as 6 km (Fautin et al., 2009) and isidid gorgonians as deep as 4 km (Roark et al.,
2005)." And they say that their own data also "provide no indication
that conditions below saturation per se dictate any overall shifts in
As for why things were as they observed them to be, the
researchers note, as highlighted by Cohen and Holcomb (2009), that one
or more cell membranes may envelope the organisms' skeletons, largely
isolating the calcification process and its associated chemistry from
the bulk seawater, citing the studies of McConnaughey (1989), Adkins et al.
(2003) and Cohen and McConnaughey (2003), which phenomenon could
presumably protect "the skeleton itself from the threat of low carbonate
dissolution." In addition, they note that "calcification is
energetically expensive, consuming up to 30% of the coral's available
resources, and that normal calcification rates can be sustained in
relatively low-carbonate environments under elevated feeding or nutrient
regimes," as described in detail by Cohen and Holcomb (2009), stating
that the likelihood that "elevated food availability could compensate
for the higher costs of calcification in heterotrophic deep-sea species
The second paper by Shamberger et al published in Marine Chemistry 127: 64-75 . They conclude: "it appears that while calcification rate and Ωarag
are correlated within a single coral reef ecosystem," as in the case of
the barrier reef of Kaneohe Bay, "this relationship does not
necessarily hold between different coral reef systems," and they state
that it can thus be expected that "ocean acidification will not affect
coral reefs uniformly and that some may be more sensitive to increasing
pCO2 levels than others," which also means (taking a more positive view of the subject) that some may be less sensitive to increasing pCO2 than others.
CO2 Science adds in light of what we know about the potential for rapid evolution in corals and their symbionts - see Evolution (Aquatic Life) in our Subject Index - we can validly maintain an even stronger positive view of the subject.
Shamberger, K.E.F., Feely, R.A., Sabine, C.L., Atkinson, M.J., DeCarlo,
E.H. and Mackenzie, F.T. 2011. Calcification and organic production on
a Hawaiian coral reef. Marine Chemistry 127: 64-75.
What was done
In a study that sheds new light on this subject, Shamberger et al.
deployed newly designed "autosamplers" to collect water samples from
the barrier coral reef of Kaneohe Bay, Oahu, Hawaii, every two hours for
six 48-hour periods, two each in June 2008, August 2009 and
January/February 2010. And based on these seawater measurements, they
calculated net ecosystem calcification (NEC) and net photosynthesis (NP) rates for these periods.
What was learned
As expected, the six scientists found that "daily NEC was strongly negatively correlated with average daily pCO2,
which ranged from 421 to 622 ppm." Most interestingly, however, they
report that "daily NEC of the Kaneohe Bay barrier reef is similar to or higher than daily NEC measured on other coral reefs, even though Ωarag levels (mean Ωarag = 2.85) are some of the lowest measured in coral reef ecosystems [italics added]."
Read more at CO2 science HERE and Here.