How does rising atmospheric CO2 affect marine organisms?

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Effects of Atmospheric CO2 Enrichment on a Marine Diatom
Sobrino, C., Ward, M.L. and Neale, P.J. 2008. Acclimation to elevated carbon dioxide and ultraviolet radiation in the diatom Thalassiosira pseudonana: Effects on growth, photosynthesis, and spectral sensitivity of photoinhibition. Limnology and Oceanography 53: 494-505.

The authors write that "among the phytoplankton species inhabiting the [ocean's] surface layer, diatoms are responsible for almost 40% of the ocean primary productivity (Nelson et al., 1995)." In addition, they say the particular species they studied -- Thalassiosira pseudonana (Husted) Hasle and Heimdal -- is "a widely distributed diatom," which gives some indication of its importance with respect to this phenomenon.

What was done
Sobrino et al. grew cultures of T. pseudonana exposed to either photosynthetically-active radiation (PAR: 400-700 nm) or PAR plus ultraviolet radiation (UVR: 280-400 nm) in 500-mL Teflon bottles at 20C using a semi-continuous approach that employed daily dilutions with fresh growth medium (filtered seawater from the Gulf Stream that was adjusted to a salinity of 15 and enriched with f/2 nutrients) through which air streams of different atmospheric CO2 concentrations (380 or 1000 ppm) were continuously bubbled.

What was learned
The three researchers determined that exposure of their seawater medium to air with an extra 620 ppm CO2 increased the photosynthetic rate of the marine diatom they studied by approximately 45% in the presence of PAR and about 60% in the presence of both PAR and UVR, while it increased the diatom's growth rate by approximately 20% in both of these radiation environments.

What it means
The results of this study continue to demonstrate that the ongoing rise in the air's CO2 content stimulates ocean productivity just as it stimulates terrestrial productivity, as is further demonstrated by the many reviews of other pertinent studies we have archived under the general heading of Marine Biota and the several sub-heading of Aquatic Plants in our Subject Index.

Nelson, D.M., Treguer, P., Brzezinski, M.A., Leynaert, A. and Queguiner, B. 1995. Production and dissolution of biogenic silica in the ocean: Revised global estimates, comparison with regional data and relationship to biogenic sedimentation. Global Biogeochemical Cycles 9: 359-372.

Reviewed 26 November 2008