Many people are worried that projected increases in the air's CO2 content could lead to ocean acidification, which is predicted to lead to marine water pH declines of 0.3 to 0.4 by the year 2100. Most of this concern derives from theoretical considerations that suggest that a pH decline of this magnitude may greatly impede the calcification process in various shellfish and corals; but the concern is widening to also include, in the words of Havenhand and Schlegel (2009), "the very earliest, and critical, process of fertilization." Hence, they decided to investigate this possibility with specimens of the oyster Crassostrea gigas, which they collected from a mixed mussel/oyster bed on the coast of western Sweden.
The collected shellfish were kept within flow-through tanks of filtered seawater that the two researchers maintained at either the normal ambient pH level or a level reduced by about 0.35 unit that was created by bubbling CO2 through the water. Under these conditions, they observed and measured the swimming behavior of the oysters' sperm and their fertilization kinetics. This work revealed that in water of pH 8.15, mean sperm swimming speeds were 92.1▒4.8Ám/s, while in water of pH 7.8 they were actually slightly higher at 94.3▒5.5Ám/s, although the difference was not statistically significant. Likewise, mean fertilization success in water of pH 8.15 was 63.4%, while in water of pH 7.8 it was also slightly higher at 64.1%, although this difference, too, was not statistically significant.
Based on these findings, the Swedish scientists concluded that "the absence of significant overall effects of pH on sperm swimming behavior and fertilization success is remarkable," emphasizing that power analyses they conducted "showed clearly that these results were not due to inadequate statistical power," and adding that "the absence of significant effect is likely a true reflection of the responses of Crassostrea gigas gametes and zygotes from the Swedish west coast to levels of CO2-induced acidification expected by the end of this century," which finding cannot help but be extremely encouraging.
Three years earlier, Berge et al. (2006) had set up five 5-liter aquariums that were continuously supplied with seawater containing a low amount of food, which they had obtained from the top meter of the Oslofjord outside the Marine Research Station of Solbergstrand in Norway, while CO2 was continuously added to the tanks' waters so as to maintain them at five different pH values (means of 8.1, 7.6, 7.4, 7.1 and 6.7) for a period of 44 days. Prior to the start of the study, numerous blue mussels (Mytilus edulis L.) of two different size classes (mean lengths of either 11 or 21 mm) had also been collected from the outer part of the Oslofjord; and 50 of each size class were introduced into each aquarium, where they were examined nearly every day for any deaths that may have occurred, after which shell lengths at either the time of death or at the end of the study were determined and compared to lengths measured at the start of the study. Simultaneously, water temperature rose slowly from 16 to 19°C during the initial 23 days of the experiment, but then declined slightly to day 31, after which it rose more rapidly to attain a maximum value of 24°C on day 39.
A lack of mortality during the first 23 days of the study showed, in the words of the authors, that "the increased concentration of CO2 in the water and the correspondingly reduced pH had no acute effects on the mussels." Thereafter, however, some mortality was observed in the highest CO2 (lowest pH) treatment from day 23 to day 37, after which deaths could also be observed in some of the other treatments; but this mortality was attributed by Berge et al. to the rapid rise in water temperature that occurred between days 31 and 39.
With respect to growth, the Norwegian researchers report that "mean increments of shell length were much lower for the two largest CO2 additions compared to the values in the controls, while for the two smallest doses the growth [was] about the same as in the control, or in one case even higher (small shells at pH = 7.6)," such that there were "no significant differences between the three aquaria within the pH range 7.4-8.1."
Berge et al. thus concluded that their results indicated that "future reductions in pH caused by increased concentrations of anthropogenic CO2 in the sea may have an impact on blue mussels," but that "comparison of estimates of future pH reduction in the sea (Caldeira and Wickett, 2003) and the observed threshold for negative effects on growth of blue mussels [which they determined to lie somewhere between a pH of 7.4 and 7.1] do however indicate that this will probably not happen in this century." Indeed, Caldeira and Wickett's calculation of the maximum level to which the air's CO2 concentration might rise yields a value that approaches 2000 ppm around the year 2300, representing a surface oceanic pH reduction of 0.7 units, which only drops the pH to the upper limit of the "threshold for negative effects on growth of blue mussels" found by Berge et al., i.e., 7.4. Consequently, blue mussels will likely never be bothered, even in the least degree, by the tendency for atmospheric CO2 enrichment to lower oceanic pH values.
In another intriguing paper, Tunnicliffe et al. (2009) discovered "dense clusters of the vent mussel Bathymodiolus brevior in natural conditions of pH values between 5.36 and 7.29 on the northwest Eifuku volcano, Mariana arc, where liquid carbon dioxide and hydrogen sulfide emerge in a hydrothermal setting," which they studied along with mussels from "two sites in the southwestern Pacific: Hine Hina in the Lau backarc basin and Monowai volcano on the Kermadec arc," where they found that "the same mussel species nestles in cracks and rubble where weak fluid flow emerges."
In the course of their exploratory endeavor, the six scientists identified four-decade-old mussels that had learned to cope with the extreme acidity of these hellish conditions, although their shell thickness and daily shell growth increments were "only about half those recorded from mussels living in water with pH > 7.8." Nevertheless, the mussels were alive; and they were doing what most climate alarmists have long claimed such creatures should not be able to do under such conditions. What is more, the six researchers note that the mussels were accompanied by "many other associated species," as reported in the study of Limen and Juniper (2006).
Tunnicliffe et al. thus write that their several findings attest to "the extent to which long-term adaptation can develop tolerance to extreme conditions." And just how extreme were the conditions in which the mussels lived? Caldeira and Wickett (2003) have calculated (1) the maximum level to which the air's CO2 concentration might rise (about 2000 ppm) due to the burning of earth's estimated fossil-fuel reserves, (2) the point in time by which that might occur (AD 2300), and (3)the related decline that might be expected to occur in ocean-surface pH (0.7 unit). These results yield a time interval of 300 years for organisms to adapt to a pH decline from about 8.1 to 7.4; and considering the much lower pH range in which the mussels studied by Tunnicliffe et al. lived, plus that of the many species studied by Limen and Juniper (5.36 to 7.29), there is ample reason to believe that even the worst case of CO2-induced acidification that can possibly be conceived would not prove a detriment to most calcifying sea life. Therefore, what will likely happen in the real world should be no problem at all.
Contemporaneously, in another effort designed to evaluate potential CO2-induced changes in shellfish calcification in the years ahead, Miller et al. (2009) grew larvae of two species of oyster -- the Eastern oyster (Crassostrea virginica) and the Suminoe oyster (Crassostrea ariakensis) -- for up to 28 days in estuarine water in equilibrium with air of four different CO2 concentrations (280, 380, 560 and 800 ppm), which were chosen to represent atmospheric conditions in the pre-industrial era, the present day, and the years 2050 and 2100, respectively, as projected by the IS92a business-as-usual scenario of the IPCC, while larval growth was assessed via image analysis and calcification by means of chemical analyses of calcium in the shells of the oyster larvae.
Following these protocols, Miller et al. found that when the larvae of both species were cultured continuously from 96 hours post fertilization for 26 to 28 days while exposed to elevated CO2 concentrations, they "appeared to grow, calcify and develop normally with no obvious morphological deformities, despite conditions of significant aragonite undersaturation," stating that these findings "run counter to expectations that aragonite shelled larvae should be especially prone to dissolution at high pCO2." More specifically, they state that "both oyster species generated larval shells that were of similar mean thickness, regardless of pCO2, Oarag [aragonite compensation point] or shell area," remarking that they "interpret the pattern of similar shell thickness as further evidence of normal larval shell development."
On top of all of these encouraging findings, it's good to remember that Tans (2009) has demonstrated that the atmosphere's CO2 concentration will likely peak well before 2100 at a maximum value of only 500 ppm, and that it will gradually drop back to what it is today some 300 or so years after that, which perturbation is much less than what is projected by the IPCC and most climate alarmists, implying a mean maximum pH excursion of only about 0.14 unit.
As a demonstration of the significance of these facts, Watson et al. (2009) studied the potential effects of IPCC-predicted future increases in CO2-driven ocean acidification on shell-producing calcification in the Sydney rock oyster (Saccostrea glomerata). In doing so, they concluded there would be a significant decline of 72% in larval survival by the year 2100. However, utilizing Watson et al.'s data, but with the maximum seawater pH decline calculated by Tans, one obtains a non-significant larval survival decline of only 14%, based on the graphical results portrayed in Watson et al.'s paper. Likewise, similar assessments of changes in antero-posterior measurement yield a significant decline of 8.7% using Watson et al.'s assumptions about ocean pH, but a non-significant decline of only 1.8% according to Tans' pH calculations, while corresponding results for dorso-ventral measurement were a significant decline of 7.5% with Watson et al.'s pH values, but a non-significant decline of only 1.5% with Tans' values.
Larval dry mass also declined, by 50% in Watson et al.'s analysis; but it experienced an actual increase (albeit non-significant) of 6% using Tans' pH analysis. And, last of all, for empty shells remaining there was a significant decline of 90% in the Watson et al. study, but a non-significant decline of only 6% when Tans' pH projections were used. Thus, whereas Watson et al. found what they called "a dramatic negative effect on the survival, growth, and shell formation of the early larval stages of the Sydney rock oyster," the use of the more realistic pH values projected by Tans imply no statistically significant reductions in any of the five biological parameters measured and evaluated by Watson et al.
Last of all, it's also good to remember that there is a large and accumulating body of research that demonstrates that extremely rapid micro-evolutionary processes are poised and ready to "kick into action" when required in almost all of earth's life forms, and that these phenomena should enable them to successfully respond to significant environmental changes at rates that correspond to the rates of those changes, as described by Balanya et al. (2006), Jump et al. (2006), Franks et al. (2007), Rae et al. (2007), Skelley et al. (2007), Van Doorslaer et al. (2007), Franks and Weis (2008), Jump et al. (2008), Purcell et al. (2008), Alford et al. (2009), Bell and Gonzalez (2009), Onoda et al. (2009) and Van Doorslaer et al. (2009).
Consequently, when all is said and done, it would appear that earth's shellfish should do just fine as the air's CO2 content continues to rise -- and gradually peaks -- near the end of the current century, as well as when it gradually returns to what it is today, some three centuries or so later, as other sources of energy are gradually "ramped up" to replace the planet's currently sufficient -- but ultimately finite and dwindling -- supplies of coal, gas and oil.
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