How does rising atmospheric CO2 affect marine organisms?

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Ocean Acidification (Effects on Marine Animals: Miscellaneous) -- Summary
In addition to the many common categories of marine animals that have been discussed in other ocean acidification Summaries, several lesser-studied sea creatures have also been scrutinized in attempts to determine their ability to tolerate projected seawater responses to the ongoing rise in the air's CO2 concentration; and in this Summary we report the results of some of those more idiosyncratic studies.

Kurihara et al. (2007) studied meiofauna, i.e., small benthic invertebrates that are larger than microfauna but smaller than macrofauna, which basically means they are metazoan animals that (1) can pass through a 0.5- to 1-mm mesh, but that (2) will be retained by a 30- to 45-Ám mesh. They obtained the little sea creatures by extracting sedimentary mud from the seafloor of Tanabe Bay on the Kii Peninsula of Japan and incubating it in marine microcosms that were continuously aerated for 56 days with air of either 360 or 2,360 ppm CO2 -- the latter of which concentrations is close to that predicted by Caldeira and Wickett (2003) to be characteristic of the real world in the year 2300 -- during which time they periodically measured the abundance and biomass of different members of the meiobenthic community contained in the sediments. In doing so, they say they observed "no significant differences in the abundance of total meiofauna, nematodes, harpacticoid copepods (including adults and copepodites) and nauplii by the end of the experiment." In fact, they say there "may have been successful recruitments under elevated CO2 conditions [italics added]," and that the elevated CO2 "had not impacted the reproduction of nematodes and harpacticoid copepods." Consequently, they concluded that "the projected atmospheric CO2 concentration in the year 2300 [should] not have acute effects on the meiofauna."

One year later, Richardson and Gibbons (2008) wrote that there had been a drop of 0.1 pH unit in the global ocean since the start of the Industrial Revolution, and that "such acidification of the ocean may make calcification more difficult for calcareous organisms," resulting in the "opening [of] ecological space for non-calcifying species." In line with this thinking, they further reported that Attrill et al. (2007) had argued that "jellyfish may take advantage of the vacant niches made available by the negative effects of acidification on calcifying plankton," causing jellyfish to become more abundant; and they additionally noted that the latter researchers provided some evidence for this effect in the west-central North Sea over the period 1971-1995. Hence, they undertook a study to see if Attrill et al.'s findings (which were claimed to be the first of their kind) could be replicated on a bigger scale.

Working with data from a larger portion of the North Sea, as well as throughout most of the much vaster Northeast Atlantic Ocean, Richardson and Gibbons used coelenterate (jellyfish) records from the Continuous Plankton Recorder (CPR) and pH data from the International Council for the Exploration of the Sea (ICES) for the period 1946-2003 to explore the possibility of a relationship between jellyfish abundance and acidic oceanic conditions. This work revealed that there were, as they describe it, "no significant relationships between jellyfish abundance and acidic conditions in any of the regions investigated." And in harmony with their findings, the two researchers further noted that "no observed declines in the abundance of calcifiers with lowering pH have yet been reported," and that echinoderm larvae in the North Sea had actually exhibited a 10-fold increase in recent times, which they say has been linked predominantly to warming by Kirby et al. (2007).

Another year closer to the present, Gooding et al. (2009) measured growth rates and feeding rates of juvenile sea stars (Pisaster ochraceus) maintained in 246-liter aquaria that were filled with re-circulating natural sea water maintained at temperatures ranging from 5 to 21°C, and which were constantly bubbled with either ambient air of 380 ppm CO2 or CO2-enriched air of 780 ppm CO2. This work revealed, as they describe it, that "the relative growth (change in wet mass/initial wet mass) of juvenile P. ochraceus increased linearly with temperature from 5°C to 21°C," and that it also responded positively to atmospheric CO2 enrichment. More specifically, they state that "relative to control treatments, high CO2 alone increased relative growth by ~67% over 10 weeks, while a 3°C increase in temperature alone increased relative growth by 110%." They also state that increased CO2 "had a positive but non-significant effect on sea star feeding rates, suggesting that CO2 may be acting directly at the physiological level to increase growth rates." Last of all, their data show that the percentage of calcified mass in the sea stars dropped from approximately 12% to 11% in response to atmospheric CO2 enrichment at 12°C, but that it did not decline further in response to a subsequent 3°C warming at either ambient or elevated CO2.

In discussing their findings, the three Canadian researchers say they demonstrate that "increased CO2 will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate should consider how different types of organisms will respond to changing climatic variables." Indeed, they clearly state -- and without equivocation -- that "responses to anthropogenic climate change, including ocean acidification, will not always be negative."

Such was also the conclusion of Ries et al. (2009), who "reared 18 calcifying species for 60 days in isothermal (25°C) experimental seawaters equilibrated with average [atmospheric] CO2 values of 409, 606, 903 and 2856 ppm, corresponding to modern CO2, and ~2, 3 and 10 times pre-industrial levels (~280 ppm), respectively, and yielding average seawater saturation states of 2.5, 2.0, 1.5 and 0.7 with respect to aragonite," after which "the organisms' net rates of calcification (total calcification minus total dissolution) under the various CO2 treatments were estimated from changes in their buoyant weight and verified with dry weight measurements after harvesting." Following these protocols, the three Woods Hole Oceanographic Institution (USA) researchers found that "in ten of the 18 species (temperate corals, pencil urchins, hard clams, conchs, serpulid worms, periwinkles, bay scallops, oysters, whelks, soft clams), net calcification decreased with increasing CO2," but that "in four of the 18 species (limpets, purple urchins, coralline red algae, calcareous green algae), net calcification increased relative to the control under intermediate CO2 levels (605 and 903 ppm), and then declined at the highest CO2 level (2856 ppm)," while "in three species (crabs, lobsters, and shrimps), net calcification was greatest under the highest level of CO2 (2856 ppm)," and, last of all, that "one species, the blue mussel, exhibited no response to elevated CO2. It should be noted, however, that the analysis of Tans (2009) shows that the highest atmospheric CO2 concentration likely to occur over the foreseeable future is only 500 ppm, so there is likely to be no significant decline in the calcification status of any of the 18 organisms studied by Ries et al., as suggested by our analysis of the similar findings of Watson et al. (2009).

In conclusion, therefore, and all things considered, there would appear to be little support for the climate-alarmist claim that the ongoing rise in the air's CO2 content will have severe negative impacts on the vast majority of the world's sea creatures.

Attrill, M.J., Wright, J. and Edwards, M. 2007. Climate-related increases in jellyfish frequency suggest a more gelatinous future for the North Sea. Limnology and Oceanography 52: 480-485.

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

Gooding, R.A., Harley, C.D.G. and Tang, E. 2009. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. Proceedings of the National Academy of Sciences, USA: 10.1073/pnas.0811143106.

Kirby, R.R., Beaugrand, G., Lindley, J.A., Richardson, A.J., Edwards, M. and Reid, P.C. 2007. Climate effects and benthic-pelagic coupling in the North Sea. Marine Ecology Progress Series 330: 31-38.

Kurihara, H., Ishimatsu, A. and Shirayama, Y. 2007. Effects of elevated seawater CO2 concentration of the meiofauna. Journal of Marine Science and Technology 15: 17-22.

Richardson, A.J. and Gibbons, M.J. 2008. Are jellyfish increasing in response to ocean acidification? Limnology and Oceanography 53: 2040-2045.

Ries, J.B., Cohen, A.L. and McCorkle, D.C. 2009. Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37: 1131-1134.

Tans, P. 2009. An accounting of the observed increase in oceanic and atmospheric CO2 and an outlook for the future. Oceanography 22: 26-35.

Watson, S.-A., Southgate, P.C., Tyler, P.A. and Peck, L.S. 2009. Early larval development of the Sydney rock oyster Saccostrea glomerata under near-future predictions of CO2-driven ocean acidification. Journal of Shellfish Research 28: 431-437.

Last updated 1 September 2010