Paper Reviewed
Liu, L., Zou, D., Jiang, H., Chen, B. and Zeng, X. 2018. Effects of increased CO2 and temperature on the growth and photosynthesis in the marine macroalga Gracilaria lemaneiformis from the coastal waters of South China. Journal of Applied Phycology 30: 1271-1280.

According to Liu et al. (2018), "relatively few studies have examined the interactive effects of rising CO2 concentration and temperature [on] algal growth and photosynthesis." Therefore, the team of five Chinese scientists set out to do just that for Gracilaria lemaneiformis, a marine red macroalga common in coastal waters that has been extensively cultivated for food and eutrophication control.

Healthy and non-reproductive thalli of the macroalgae were collected from a cultivation field at Nanao Island, Shantou, China (23.33°N, 116.92°E), and brought back to a laboratory where they were cultured under either ambient (390 ppm) or elevated (700 ppm) CO2 and ambient (20°C) or elevated (24°C) temperature. Following ten days of cultivation, Liu et al. report that the growth rates of G. lemaneiformis were "significantly improved by increasing temperature, especially under concurrent increasing CO2 levels," adding that "increased temperature exerted more pronounced effects on the growth and photosynthesis of G. lemaneiformis than increased CO2 concentrations did." Nevertheless, as shown in the figure below, elevated CO2, whether alone or in combination with high temperature, stimulated macroalga fresh weight.

In light of the findings noted above, Liu et al. conclude that "sea cultivation of G. lemaneiformis would benefit from the ongoing climate change (increasing atmospheric CO2 concentrations and sea surface temperatures) through enhanced growth and photosynthesis, which thereby would improve the carbon sequestration of seaweed mariculture."

Figure 1. The fresh weights and relative growth rates (insert) of Gracilaria lemaneiformis grown under different CO2 (390 or 700 ppm) and temperature (20 or 24°C) treatments. AC = 390 ppm CO2 and 20°C, HC = 700 ppm CO2 and 20°C, HT = 390 ppm CO2 and 24°C, GH = 700 ppm CO2 and 24°C. Source: Liu et al. (2018).