How does rising atmospheric CO2 affect marine organisms?

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The Productivity Response of Six Macroalgal Species to Ocean Acidification and Warming

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

Introducing their study, Hernández et al. write 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," especially research that examines "the combined effects between raised temperatures and increased CO2, as these effects may combine to affect algal species composition, abundance and productivity worldwide." Consequently, the four researchers designed an experiment to assess the combined influence of temperature and elevated pCO2 on the productivity of six macroalgae species.

Work was conducted in a controlled environment using samples from six key species common to the Canary Islands: Corallina caespitosa, Pterocladiella capillacea, Padina pavonica, Cystoseira abies-marina, Lobophora variegata and Canistrocarpus cervicornis. The six species are important inhabitants of surrounding shallow subtidal communities and together constitute more than 70% of the total macroalgal cover. The full-factorial experiment included four temperature (19, 21, 23 and 25°C) and three seawater pH treatments (8.1, 7.7 and 7.4). Key data measurements included oxygen production and depletion in order to estimate net primary production and respiration.

In describing their findings, Hernández et al. report "there was a significant effect of pH on algal productivity and this was consistent among the selected species of algae [such that] productivity was significantly greater at pH 7.4 and 7.7 compared to pH 8.1." The impact of temperature on net primary productivity, in contrast, varied among species; one seaweed had the highest production at 19°C, three others at 21°C and two at 25°C.

With respect to algal respiration, the authors note this parameter "varied significantly with temperature and among species and was higher at [the coldest temperature of] 19°C." Although such finding "contradicts the known response of increased respiration rate with temperature," Hernández et al. suggest is was likely observed because the species examined are more tropical in nature and likely "acclimate to high temperatures by lowering their carbon loss due to respiration as temperature rises." Seawater pH, on the other hand, had no impact on respiration rates, indicating in the words of the authors "that inorganic carbon availability in seawater has no influence on this metabolic process."

In concluding their paper, the authors write their results "suggest that a lower-pH ocean, according to current predictions, would enhance primary production in the studied algal species," albeit an "associated increase in temperature would have varied effects." Such an assessment is refreshingly different from the doom and gloom scenarios that climate alarmists consistently insist will befall marine life in the future.

Posted 18 May 2020