How does rising atmospheric CO2 affect marine organisms?

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Ocean Acidification and Hypoxia: Double Trouble for Tubeworms?
Mukherjee, J., Wong, K.K.W., Chandramouli, K.H., Qian, P.-Y., Leung, P.T.Y., Wu, R.S.S. and Thiyagarajan, V. 2013. Proteomic response of marine invertebrate larvae to ocean acidification and hypoxia during metamorphosis and calcification. The Journal of Experimental Biology 216: 4580-4589.

The authors write that the majority of marine invertebrates "have complex life cycles that include an intricately controlled metamorphic process involving the transformation from swimming (planktonic) larvae to sessile (attached or benthic) adults in a few minutes," citing Qian (1999) and Hadfield (2000), which transformation, in their words, "is one of the most challenging processes in the life history of an organism, requiring the simultaneous performance of multiple tasks." And they go on to say that "with rising anthropogenic CO2-driven changes to the global climate system, larvae now face unprecedented threats from multiple stressors associated with climate change," one of which is ocean acidification (OA).

Concurrently, they also note that "anthropogenic activities such as the discharge of excessive nutrients, sewage and agricultural fertilizers are causing coastal waters to become increasingly nutrient rich (Howarth et al., 2011)," such that they sustain increases in algal production to the point that "this excessively produced biomass eventually decomposes, resulting in dead zones, areas of hypoxia that have become deprived of dissolved oxygen," citing Ekau et al. (2010) and Rabalais et al. (2010) in this regard. And they thus make the point that as time marches on and these conditions worsen, "the ability of larvae to successfully metamorphose and build their calcareous tubes is likely to be compromised as a direct consequence of the combined effect of OA and hypoxia."

What was done
In a test of this hypothesis, Mukherjee et al. say they "investigated the proteomic response of metamorphosing larvae of the tubeworm Hydroides elegans, challenged with two climate change stressors, ocean acidification (pH 7.6) and hypoxia (2.8 mg O2 per liter)," as well as with both of the stressors combined.

What was learned
The seven scientists found that concomitant exposure to the two climate change stressors "caused several proteins involved in energy metabolism, calcification and stress tolerance to be differentially expressed." And they say that this phenomenon "seemed to allow the tubeworm larvae to successfully metamorphose and carry out calcification."

What it means
As a result of their findings, Mukherjee et al. concluded that "the aragonite tube-forming tubeworm larvae have a high tolerance to hypoxia and may possess the capacity to acclimate over time, even in the phase of ocean acidification."

Ekau, W., Auel, H., Portner, H.O. and Gilbert, D. 2010. Impacts of hypoxia on the structure and processes in pelagic communities (zooplankton, macro-invertebrates and fish). Biogeosciences 7: 1669-1699.

Hadfield, M.G. 2000. Why and how marine invertebrate larvae metamorphose so fast. Seminars in Cell & Developmental Biology 11: 437-443.

Howarth, R., Chan, F., Conley, D.J., Garnier, J., Doney, S.C., Marino, R. and Billen, G. 2011. Coupled biogeochemical cycles: eutrophication and hypoxia in temperate estuaries and coastal marine ecosystems. Frontiers in Ecology and the Environment 9: 18-26.

Qian, P.Y. 1999. Larval settlement of polychaetes. Hydrobiologia 402: 239-253.

Rabalais, N.N., Diaz, R.J., Levin, L.A., Turner, R.E., Gilbert, D. and Zhang, J. 2010. Dynamics and distribution of natural and human-caused hypoxia. Biogeosciences 7: 585-619.

Reviewed 5 March 2014