How does rising atmospheric CO2 affect marine organisms?

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Calcareous Green Algae Tolerating OA Conditions at a CO2 Seep

Paper Reviewed
Vogel, N., Fabricius, K.E., Strahl, J., Noonan, S.H.C., Wild, C. and Uthicke, S. 2015. Calcareous green alga Halimeda tolerates ocean acidification conditions at tropical carbon seeps. Limnology and Oceanography 60: 263-275.

Noting that organisms living near natural volcanic seeps are often acclimatized -- and in some cases even adapted -- to elevated CO2 environments, Vogel et al. (2015) write that volcanic CO2 seeps thus provide an opportunity to identify which organisms are capable of living in elevated CO2 conditions projected to occur globally just a few decades from now. And, therefore, they investigated various ecological, physiological and skeletal characteristics of the calcifying green alga Halimeda growing in the vicinity of natural CO2 seeps (pH ~7.8) and compared them to those observed at control reefs exhibiting ambient CO2 conditions (pH ~8.1).

This work revealed, as the six scientists report, that for each of the two most abundant species (H. digitata and H. opuntia), rates of calcification in the light increased at the high CO2 site compared to controls by 131% and 41%, respectively. In the dark, on the other hand, they say that "calcification was not affected by elevated CO2 in H. digitata, whereas it was reduced by 167% in H. opuntia, suggesting nocturnal decalcification." However, they also found that 24-hour net calcification was similar between seep and control sites, implying that the increased calcification when exposed to normal daylight more than compensated for the reduced dark calcification in H. opuntia.

Based on the findings of their study of "long-term exposure in a natural environment with natural light, nutrient and flow regimes," Vogel et al. thus conclude -- in the final sentence of their paper's abstract -- that the Halimeda spp. they investigated "can acclimatize and will likely still be capable to grow and calcify in PCO2 conditions exceeding most pessimistic future CO2 projections."

Posted 26 May 2015