How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Calcification (Other Marine Organisms) -- Summary
For some time now, the ongoing rise in the atmosphere's CO2 concentration has been claimed to be raising havoc - or just about to be doing so - with earth's calcifying marine organisms by lowering the calcium carbonate saturation state of seawater, which phenomenon has been predicted to greatly hamper the abilities of these creatures to produce their calcium carbonate skeletons (Orr et al., 2005). In the companion category of Calcification (Corals) in our Subject Index, we discuss this subject as it applies to earth's many species of coral. Here, we describe the results of studies of other calcifying marine organisms that have explored this same phenomenon.

Riebesell (2004) described the results of CO2 perturbation experiments conducted south of Bergen, Norway, where nine 11-m3 enclosures moored to a floating raft were aerated in triplicate with CO2-depleted, normal and CO2-enriched air of 190, 370 and 710 ppm CO2 in order to simulate glacial, present-day and predicted end-of-the-century atmospheric CO2 conditions, respectively. In the course of this study, a mixed phytoplankton bloom developed, and, as Riebesell describes it, "significantly higher net community production was observed under elevated CO2 levels during the build-up of the bloom." In addition, Riebesell reports that "CO2-related differences in primary production continued after nutrient exhaustion, leading to higher production of transparent exopolymer particles under high CO2 conditions," something that has also been observed by Engel (2002) in a natural plankton assemblage and by Heemann (2002) in monospecific cultures of both diatoms and coccolithophores.

Another important finding of this experiment was that the community that developed under the high CO2 conditions expected for the end of this century was dominated by the coccolithophore Emiliania huxleyi. Consequently, Riebesell finds even more reason to believe that "coccolithophores may benefit from the present increase in atmospheric CO2 and related changes in seawater carbonate chemistry," in contrast to the many negative predictions that have been made about rising atmospheric CO2 concentrations in this regard. Also, in further commentary on the topic, Riebesell states that "increasing CO2 availability may improve the overall resource utilization of E. huxleyi and possibly of other fast-growing coccolithophore species," and he concludes that "if this provides an ecological advantage for coccolithophores, rising atmospheric CO2 could potentially increase the contribution of calcifying phytoplankton to overall primary production." In fact, noting that "a moderate increase in CO2 facilitates photosynthetic carbon fixation of some phytoplankton groups," including "the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica" - and in a major challenge to the climate-alarmist claim that atmospheric CO2 enrichment will harm such marine organisms - Riebesell suggests that "CO2-sensitive taxa, such as the calcifying coccolithophorids, should therefore benefit more [our italics] from the present increase in atmospheric CO2 compared to the non-calcifying diatoms."

Working with two previously untested coccolithophores, Calcidiscus leptoporus and Coccolithus pelagicus, which they describe as "two of the most productive marine calcifying species," Langer et al. (2006) conducted batch-culture experiments in which they observed a "deterioration of coccolith production above as well as below present-day CO2 concentrations in C. leptoporus," and a "lack of a CO2 sensitivity of calcification in C. pelagicus" over an atmospheric CO2 concentration range of 98-915 ppm. Both of these observations, in their words, "refute the notion of a linear relationship of calcification with the carbonate ion concentration and carbonate saturation state," which refuted notion is championed by the world's climate alarmists. In an apparent negative finding, however, particularly in the case of C. leptoporus, Langer et al. observed that although their experiments revealed that "at 360 ppm CO2 most coccoliths show normal morphology," at both "higher and lower CO2 concentrations the proportion of coccoliths showing incomplete growth and malformation increases notably."

To determine if such deleterious responses might have also occurred in the real world at different times in the past, the researchers studied coccolith morphologies in six sediment cores obtained along a range of latitudes in the Atlantic Ocean. As they describe it, this work revealed that changes in coccolith morphology similar to those "occurring in response to the abrupt CO2 perturbation applied in experimental treatments are not [our italics] mirrored in the sedimentary record." This finding indicates, as they suggest, that "in the natural environment C. leptoporus has adjusted to the 80-ppm CO2 and 180-ppm CO2 difference between present [and] preindustrial and glacial times, respectively."

In further discussing these observations, Langer et al. say "it is reasonable to assume that C. leptoporus has adapted its calcification mechanism to the change in carbonate chemistry having occurred since the last glacial maximum," suggesting as a possible explanation for this phenomenon that "the population is genetically diverse, containing strains with diverse physiological and genetic traits, as already demonstrated for E. huxleyi (Brand, 1981, 1982, 1984; Conte et al., 1998; Medlin et al., 1996; Paasche, 2002; Stolte et al., 2000)." They also state that this adaptive ability "is not likely to be confined to C. leptoporus but can be assumed to play a role in other coccolithophore species as well," which leads them to conclude that such populations "may be able to evolve so that the optimal CO2 level for calcification of the species tracks the environmental value [our italics]." With respect to the future, therefore, Langer et al. end on a strongly positive note, stating that "genetic diversity, both between and within species, may allow calcifying organisms to prevail in a high CO2 ocean."

In a study of a very different creature, Berge et al. (2006) continuously supplied five 5-liter aquariums with low-food-content sea water that was extracted from the top meter of the Oslofjord outside the Marine Research Station Solbergstrand in Norway, while CO2 was continuously added to the waters of the aquaria 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, blue mussels (Mytilus edulis) of two different size classes (mean lengths of either 11 or 21 mm) were collected from the outer part of the Oslofjord, and 50 of each size class were introduced into each aquarium, where they were examined close to daily 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 19C during the initial 23 days of the experiment, but then declined slightly to day 31, after which it rose rapidly to attain a maximum value of 24C on day 39.

A lack of mortality during the first 23 days of the study showed, in the words of the researchers, 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, which mortality Berge et al. attributed to the rapid increase 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. say their results "indicate 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.

Last of all, in evaluating global seawater impacts of (1) model-predicted global warming and (2) direct seawater chemical consequences of a doubling of the air's CO2 content, Loaiciga (2006) used a mass-balance approach to (1) "estimate the change in average seawater salinity caused by the melting of terrestrial ice and permanent snow in a warming earth," and he (2) applied "a chemical equilibrium model for the concentration of carbonate species in seawater open to the atmosphere" in order to "estimate the effect of changes in atmospheric CO2 on the acidity of seawater." Assuming that the rise in the planet's mean surface air temperature continues unabated, and that it eventually causes the melting of all terrestrial ice and permanent snow, Loaiciga calculated that "the average seawater salinity would be lowered not more than 0.61%o from its current 35%o." He also reports that across the range of seawater temperature considered (0 to 30C), "a doubling of CO2 from 380 ppm to 760 ppm increases the seawater acidity [lowers its pH] approximately 0.19 pH units." He thus concludes that "on a global scale and over the time scales considered (hundreds of years), there would not be accentuated changes in either seawater salinity or acidity from the rising concentration of atmospheric CO2."

In light of the findings of these diverse studies, it would appear that any changes that might occur in the chemistry of the world's oceans in response to any changes that might occur in the atmosphere's CO2 concentration would have little to no negative impacts on calcifying marine organisms, all of the rantings and ravings of the world's climate alarmists notwithstanding.

Berge, J.A., Bjerkeng, B., Pettersen, O., Schaanning, M.T. and Oxnevad, S. 2006. Effects of increased sea water concentrations of CO2 on growth of the bivalve Mytilus edulis L. Chemosphere 62: 681-687.

Brand, L.E. 1981. Genetic variability in reproduction rates in marine phytoplankton populations. Evolution 38: 1117-1127.

Brand, L.E. 1982. Genetic variability and spatial patterns of genetic differentiation in the reproductive rates of the marine coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. Limnology and Oceanography 27: 236-245.

Brand, L.E. 1984. The salinity tolerance of forty-six marine phytoplankton isolates. Estuarine and Coastal Shelf Science 18: 543-556.

Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

Conte, M., Thompson, A., Lesley, D. and Harris, R.P. 1998. Genetic and physiological influences on the alkenone/alkenonate versus growth temperature relationship in Emiliania huxleyi and Gephyrocapsa oceanica. Geochimica et Cosmochimica Acta 62: 51-68.

Engel, A. 2002. Direct relationship between CO2 uptake and transparent exopolymer particles production in natural phytoplankton. Journal of Plankton Research 24: 49-53.

Heemann, C. 2002. Phytoplanktonexsudation in Abhangigkeit der Meerwasserkarbonatchemie. Diplom. Thesis, ICBM, University of Oldenburg, Germany.

Langer, G. and Geisen, M., Baumann, K.-H., Klas, J. , Riebesell, U., Thoms, S. and Young, J.R. 2006. Species-specific responses of calcifying algae to changing seawater carbonate chemistry. Geochemistry, Geophysics, Geosystems 7: 10.1029/2005GC001227.

Loaiciga, H.A. 2006. Modern-age buildup of CO2 and its effects on seawater acidity and salinity. Geophysical Research Letters 33: 10.1029/2006GL026305.

Medlin, L.K., Barker, G.L.A., Green, J.C., Hayes, D.E., Marie, D., Wreiden, S. and Vaulot, D. 1996. Genetic characterization of Emiliania huxleyi (Haptophyta). Journal of Marine Systems 9: 13-32.

Orr, J.C., Fabry, V.J., Aumont, O., Bopp, L., Doney, S.C., Feely, R.A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., Key, R.M., Lindsay, K., Maier-Reimer, E., Matear, R., Monfray, P., Mouchet, A., Najjar, R.G., Plattner, G.-K., Rodgers, K.B., Sabine, C.L., Sarmiento, J.L., Schlitzer, R., Slater, R.D., Totterdell, I.J., Weirig, M.-F., Yamanaka, Y. and Yool, A. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437: 681-686.

Paasche, E. 2002. A review of the coccolithophorid Emiliania huxleyi ((Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions. Phycologia 40: 503-529.

Riebesell, U. 2004. Effects of CO2 enrichment on marine phytoplankton. Journal of Oceanography 60: 719-729.

Stolte, W., Kraay, G.W., Noordeloos, A.A.M. and Riegman, R. 2000. Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker. Journal of Phycology 96: 529-589.

Last updated 18 July 2007