Paper Reviewed
Horwitz, R., Borell, E.M., Yam, R., Shemesh, A. and Fine, M. 2015. Natural high pCO2 increases autotrophy in Anemonia viridis (Anthozoa) as revealed from stable isotope (C, N) analysis. Scientific Reports 5: 10.1038/srep08779.

In a study conducted along a natural pCO2 gradient in the Levante Bay of Italy's Vulcano Island in the Mediterranean Sea -- where seawater chemistry varies along a distance of several hundred meters moving away from a seabed venting source -- Horwitz et al. (2015) studied the natural variability of carbon and nitrogen isotopes in the symbiotic sea anemone Anemonia viridis to see if any dietary shifts occur in the anemone's autotrophic/heterotrophic balance in response to the ocean acidification gradient that exists between the undisturbed seabed and the source of the vented CO2. And what did they thereby learn?

In the words of the four researchers, their results demonstrate "the adaptation and potential resilience of A. viridis to acidification conditions, as physiological data (i.e. protein content, Symbiodinium density and chlorophyll a concentration), along with δ15N values and C/N ratios, remained unaffected among sites along the pCO2 gradient," while they additionally opine that "the high pCO2 environment probably stimulated cell division of algal symbionts."

In light of these findings, Horwitz et al. were able to determine that "the anemone host relies more on photosynthetically derived carbon under elevated pCO2," and they thus propose that "A. viridis optimizes energy utilization under elevated pCO2 through an increased autotrophic input," although their isotopic data showed that "heterotrophy is maintained as an additional source of energy/nutrients," all of which leads them to conclude that "these factors may contribute, at least in part, to the increased size and abundance of the A. viridis population proximate to the vent site," which had earlier been both observed and reported by Suggett et al. (2012).

References
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.