How does rising atmospheric CO2 affect marine organisms?

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Would Sea Anemones Survive in a High-CO2 World of the Future?
Suggett, D.J., Hall-Spencer, J.M., Rodolfo-Metalpa, R., Boatman, T.G., Payton, R., Pettay, D.T., Johnson, V.R., Warner, M.E. and Lawson, T. 2012. Sea anemones may thrive in a high CO2 world. Global Change Biology 18: 3015-3025.

The authors write that "non-calcifying anthozoans such as soft corals and anemones, play important ecological and biogeochemical roles in reef environments (e.g. Fitt et al., 1982; Bak and Borsboom, 1984; Muller-Parker and Davy, 2001)," and as with reef-forming scleractinian corals, they note that in order to supplement their nutritional requirements, "many anemones harbor symbiotic algae (Symbiodinium spp.)." Yet in spite of these significant similarities, they indicate that little is known about how these organisms would respond to a future acidification of the world's oceans.

What was done
Focusing on this particular dearth of information, Suggett et al. collected pertinent data from the 11th to the 26th of May 2011 on a sea anemone (Anemonia viridis) along a natural seawater pH gradient of 8.2-7.6 - such as would be expected to prevail across an atmospheric CO2 gradient of 365-1425 ppm - which was produced by a shallow cold vent system (Johnson et al., 2011, 2012) that released CO2 to coastal waters near Vulcano, Italy, about 25 km northeast of Sicily.

What was learned
The nine researchers say their physiological measurements revealed an increase in gross maximum photosynthesis and respiration rates, but with the increase in photosynthesis being greater than the increase in respiration, as well as increased dinoflagellate endosymbiont abundance (but unchanged diversity) with increasing CO2, with the result that sea anemone abundance increased with CO2 and "dominated the invertebrate community at high CO2 conditions."

What it means
Suggett et al. say that the enhanced productivity they observed in the sea anemones they studied implies "an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater CO2." And, therefore, they declare in the title of their paper that "Sea anemones may thrive in a high CO2 world."

Bak, R.P.M. and Borsboom, J.L.A. 1984. Allelopathic interaction between a reef coelenterate and benthic algae. Oecologia 63: 194-198.

Fitt, W.K., Pardy, R.L. and Littler, M.M. 1982. Photosynthesis, respiration, and contribution to community productivity of the asymbiotic sea anemone Anthopleura elegantissima. Journal of Experimental Marine Biology and Ecology 61: 213-232.

Johnson, V.R., Brownlee, C., Rickaby, R.E.M., Graziano, M., Milazzo, M. and Hall-Spencer, J.M. 2011. Responses of marine benthic microalgae to elevated CO2. Marine Biology 158: 2389-2404.

Johnson, V.R., Russell, B.D., Fabricius, K.E., Brownlee, C. and Hall-Spencer, J.M. 2012. Temperate and tropical brown macroalgae thrive, despite decalcification, along natural CO2 gradients. Global Change Biology 18: 2792-2803.

Muller-Parker, M. and Davy, S.K. 2001. Temperate and tropical algal-sea anemone symbioses. Invertebrate Biology 120: 104-123.

Reviewed 6 March 2013