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Ocean Acidification Impacts on Cnidarian-Dinoflagellate Symbioses

Paper Reviewed
Gibbin, E.M. and Davy, S.K. 2014. The photo-physiological response of a model cnidarian-dinoflagellate symbiosis to CO2-induced acidification at the cellular level. Journal of Experimental Marine Biology and Ecology 457: 1-7.

In the words of Gibbin and Davy (2014), "there is growing evidence that increased CO2 availability associated with ocean acidification could enhance primary productivity in Symbiodinium cells, citing Marubini et al. (2008), Brading et al. (2011), Suggett et al. (2012), Towanda and Thuesen (2012) and Jarrold et al. (2013). And they state that this phenomenon "may limit the potential for host cell acidosis," citing Gibbin et al. (2014). However, they note that "to date, no study has examined the longer-term impacts of CO2-addition on both host and symbiont pHi [intracellular pH] in the cnidarian-dinoflagellate symbiosis."

Determined to fill this experimental void, Gibbin and Davy investigated the relationship between photo-physiology and pHi by exposing the sea anemone Aiptasia sp. to three different sets of seawater pH: 8.14 ± 0.01, 7.83 ± 0.01 and 7.54 ± 0.02 - corresponding to pCO2 concentrations of 289.94 ± 12.54, 687.40 ± 25.10 and 1459.92 ± 65.51 µatm - for a period of two months, during which time they measured a suite of physiological responses, including maximum dark-adapted fluorescent yield of PSII, gross photosynthetic rate, respiration rate, symbiont population density, and pHi of both the dinoflagellate symbiont and the host anemone.

In discussing their findings the two New Zealand researchers report that the intermediate treatment symbiont densities were 32% higher than in the control treatment by the end of the experiment, while densities in the high CO2 treatment had increased by 54% after the experiment's second week and by 81% at the conclusion of the experiment. In addition, they found that "under intermediate CO2 addition, a two-fold increase in gross photosynthesis (Pgross) was evident by week 2, which remained more or less constant thereafter." And in comparison, they say that "exposure to high CO2 induced a 2.5-fold increase in Pgross after two weeks, and an almost 4-fold increase from week 6 onwards," with the final result that "over the duration of the experiment, cell-specific photosynthetic rate increased by 81.6% and 114% in the intermediate and high CO2 treatments, respectively."

In the words of Gibbin and Davy, "our results, along with those of Suggett et al. (2012), suggest that symbiotic sea anemones could not only survive ocean acidification, but also thrive under future conditions."

References
Brading, P., Warner, M.E., Davey, P., Smith, D.J., Achterberg, E.P. and Suggett, D.J. 2011. Differential effects of ocean acidification on growth and photosynthesis among phylotypes of Symbiodinium (Dinophyceae). Limnology and Oceanography 56: 927-938.

Gibbin, E.M., Putnam, H.M., Davy, S.K. and Gates, R.D. 2014. Journal of Experimental Biology: 10.1242/jeb.099549.

Jarrold, M.D., Calosi, P., Verberk, W.C., Rastrick, S.P., Atfield, A. and Spicer, J.I. 2013. Physiological plasticity preserves the metabolic relationship of the intertidal non-calcifying anthozoan-Symbiodinium symbiosis under ocean acidification. Journal of Experimental Marine Biology and Ecology 449: 200-206.

Marubini, F., Ferrier-Pages, C., Furla, P. and Allemand, D. 2008. Coral calcification responds to seawater acidification: a working hypothesis towards a physiological mechanism. Coral Reefs 27: 491-499.

Suggett, D.J., Hall-Spencer, J.M., Rodolfo-Metalpa, R., Boatman, T.G., Payton, R., Tye Pettay, D., 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.

Towanda, T. and Thuesen, E.V. 2012. Prolonged exposure to elevated CO2 promotes growth of the algal symbiont Symbiodinium muscatinei in the intertidal sea anemone Anthopleura elegantissima. Biology Open 1: 615-621.

Posted 8 October 2014