How does rising atmospheric CO2 affect marine organisms?

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The Impacts of Elevated CO2 on the Productivity of Six Macroalgal Species

Paper Reviewed
Hernández, C.A., Sangil, C., Fanai, A. and Hernández, J.C. 2018. Macroalgal response to a warmer ocean with higher CO2 concentration. Marine Environmental Research 136: 99-105.

Writing as background for their work, Hernández et al. (2018) say that "to increase the knowledge of the impact of ocean acidification on aquatic ecosystems, more studies showing the impact of elevated pCO2 on both calcareous and non-calcareous macroalgae are needed," including research that examines "the combined effects between raised temperatures and increased CO2 concentration, as these effects may combine to affect algal species composition, abundance and productivity worldwide." Therefore, this team of four European researchers set out to assess the combined effects of these two parameters (pCO2 and temperature) "on the short-term photosynthetic and respiration rates of different key or engineer seaweed species, so as to predict the impact of global change on their productivity."

Six different macroalgae species were studied (Corallina caespitosa, Pterocladiella capillacea, Padina pavonica, Cystoseira abies-marina, Lobophora variegate and Canistrocarpus cervicornis), all of which are important components of subtidal coastal communities in the Canary Islands where they constitute more than 70% of the macroalgal cover. The selected pH and temperature treatments included 8.1, 7.7 and 7.4 for pH and 19, 21, 23 and 25°C for temperature.

In discussing their findings, Hernández et al. report that algal productivity was significantly enhanced at the lower pH values (7.4 and 7.7) relative to ambient (pH of 8.1), which observation was "consistent among [all] the selected species of algae." In contrast, primary production was less consistent with increasing temperature; two of the species showed increases as temperature increased, one depicted a decrease, and three exhibited little change, based upon visual inspection of data presented in the authors' Figure 2.

With respect to respiration, rates were unaffected by pH levels, but significantly impacted by temperature. However, the impact was such that respiration rates decreased with increasing temperature, suggesting the plants acclimated to the higher temperatures by "lowering their carbon loss." Consequently, in light of their several findings, Hernández et al. conclude that "a lower-pH ocean, according to current predictions, would enhance primary production in the studied algal species."

Posted 19 September 2018