Paper Reviewed
Kim, J.-H., Kim, N., Moon, H., Lee, S., Jeong, S.Y., Diaz-Pulido, G., Edwards, M.S., Kang, J.-H., Kang, E.J., Oh, H.-J., Hwang, J.-D. and Kim, I.-N. 2020. Global warming offsets the ecophysiological stress of ocean acidification on temperate crustose coralline algae. Marine Pollution Bulletin 157: 111324.

Crustose coralline algae (CCA) are calcifying seaweeds that inhabit intertidal and subtidal zones all across the ocean. They are ecologically important in that they contribute to primary production and carbonate sand production, facilitate invertebrate larval settlement and provide habitat for numerous marine species. Given such contributions to coastal habitats and systems ecology, Kim et al. (2020) say it "is important to understand the potential mechanisms of adaptation of CCA to future climate change conditions." Consequently, this twelve-member research team designed an experiment to "test the independent and combined effects of ocean acidification and ocean warming on a dominant CCA species in the temperate coastal region.

The species they chose is the coralline red algae Chamberlainium sp. Specimens were collected from tidal pools in Garorim Bay (Seosan, Chungcheongnam-do, Korea) and brought back to the laboratory for an indoor mesocosm study. Treatment conditions included two temperatures (20°C or 25°C) and two pCO2 concentrations (450 µatm or 900 µatm) over a period of 47 days. Specifically, the four treatments were control (20°C and 450 µatm), ocean acidification (20°C and 900 µatm), ocean warming (25°C and 450 µatm) and combined ocean acidification and warming (25°C and 900 µatm).

The results of the study revealed that among the four treatments productivity was lowest under ocean acidification alone. Similarly, specific growth rates were lowest in the ocean acidification treatment. And if the study would have stopped there, including only an investigation into ocean acidification, the future would have looked awfully bad for this CCA species. However, these negative responses were counterbalanced by elevated temperature, where Kim et al. report "warming offsets the negative effects of acidification by creating more suitable conditions for photosynthesis and growth." In fact, the highest growth rates of all the treatments were observed in the combined ocean acidification and warming treatment. Consequently, since ocean acidification and ocean warming are predicted to occur in tandem, it would appear that the future outlook for this CCA species is one in which these two projected stressors will induce no growth-related stress!