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The Phenotypic Plasticity of a Colonial Bryozoan

Paper Reviewed
Swezey, D.S., Bean, J.R., Hill, T.M., Gaylord, B., Ninokawa, A.T. and Sanford, E. 2017. Plastic responses of bryozoans to ocean acidification. Journal of Experimental Biology 220: 4399-4409.

Bryozoans are tiny aquatic animals that typically live in colonies. Celleporella cornuta is one such example from the intertidal and subtidal habitats off the coast of California, where its larvae settle and form colonies composed of male, female and non-sexual interconnected units.

Evaluating the ability of this colonial marine species (C. cornuta) to adapt to global environmental change was the topic of a recent investigation by Swezey et al. (2017), who set out to determine "whether phenotypic plasticity mediates the responses of bryozoan colonies to ocean acidification." The researchers accomplished this objective by performing a laboratory experiment in which they subjected populations of C. cornuta to normal (400 µatm) or elevated (1150 µatm) CO2 seawater conditions over a period of eight weeks. And what did their study reveal?

In the words of the authors, the bryozoan colonies were "remarkably plastic" to ocean acidification, such that "colonies raised under high CO2 grew more quickly, investing less in reproduction and producing lighter skeletons when compared with genetically identical clones raised under current surface atmosphere CO2 values." In addition, Swezey et al. report that C. cornuta colonies in the high CO2 treatment "changed the Mg/Ca ratio of skeletal calcite and increased the expression of organic coverings in new growth, which may serve as protection against acidified water."

Consequently, and in light of these several findings, the six scientists conclude by saying their results "demonstrate that phenotypic plasticity and energetic trade-offs can mediate biological responses to global environmental change, and highlight the broad range of strategies available to colonial organisms." And based on these facts, they write that their findings "provide a cautionary note about the complexity of responses to global change, and add to recent calls (Chevin et al., 2010; Munday et al., 2013) for greater attention to the role that plasticity will play in mediating the responses of natural populations to global change." In other words, predictions of widespread demise of marine life due to ocean acidification are overblown and unlikely to occur.

References
Chevin, L.-M, Lande, R. and Mace, G.M. 2010. Adaptation, plasticity, and extinction in a changing environment: towards a predictive theory. PLoS Biology 8: e1000357.

Munday, P.L., Warner, R.R., Monro, K., Pandolfi, J.M. and Marshall, D.J. 2013. Predicting evolutionary responses to climate change in the sea. Ecology Letters 16: 1488-1500.

Posted 5 April 2018