Algae 2020, 35(4): 375-388 https://doi.org/10.4490/algae.2020.35.12.8 Open Access Research Article Copyright © 2020 The Korean Society of Phycology 375 http://e-algae.org pISSN: 1226-2617 eISSN: 2093-0860 Effect of elevated pCO 2 on thermal performance of Chattonella marina and Chattonella ovata (Raphidophyceae) Myeong Hwan Lim 1,2 , Chung Hyeon Lee 1,2 , Juhee Min 1,2 , Hyun-Gwan Lee 1,2 and Kwang Young Kim 1,2, * 1 Department of Oceanography, College of Natural Sciences, Chonnam National University, Gwangju 61186, Korea 2 Marine Ecosystem Disturbing and Harmful Organisms (MEDHO) Research Center, Gwangju 61186, Korea Ocean acidification and warming, identified as environmental concerns likely to be affected by climate change, are crucial determinants of algal growth. The ichthyotoxic raphidophytes Chattonella species are responsible for huge eco- nomic losses and environmental impact worldwide. In this study, we investigated the impact of CO 2 on the thermal performance curves (TPCs) of Chattonella marina and Chattonella ovata grown under temperatures ranging from 13 to 34°C under ambient pCO 2 (350 μatm) and elevated pCO 2 (950 μatm). TPCs were comparable between the species or even between pCO 2 levels. With the exception of the critical thermal minimum (CT min ) for C. ovata, CT min for C. marina and the thermal optimum (T opt ) and critical thermal maximum (CT max ) for both species did not change with elevation of pCO 2 levels. While CO 2 enrichment increased the maximum photosynthetic rates (P max ) up to 125% at the T opt of 30°C, specific growth rates were not significantly different under elevated pCO 2 for the two species. Overall, C. ovata is likely to benefit from climate change, potentially widening its range of thermal tolerance limit in highly acidic waters and contributing to prolonged phenology of future phytoplankton assemblages in coastal waters. Key Words: Chattonella marina; Chattonella ovata; growth rate; ocean acidification; photosynthetic rate; thermal per- formance curve; warming INTRODUCTION Climate change scenarios have predicted a global mean temperature rise of 2.6-4.8°C by the end of this cen- tury (Core Writing Team et al. 2014), which could affect the changes in the biogeographic range of marine species and cause a substantial pole-ward extension of biodiver- sity across the North Pacific (Hazen et al. 2013). Concur- rently, the global average sea surface temperature (SST) has increased by 0.7°C while decreasing the pH by 0.1 units since pre-industrial times. SST is expected to rise by a further 1.2-3.2°C, and pH is expected to fall by a fur- ther 0.3-0.4 units by the year 2100 according to the Rep- resentative Concentration Pathway 8.5 (RCP8.5) (Gattuso et al. 2015). These environmental changes could affect the potentially significant role of phytoplankton in re- moving CO 2 from the sunlit ocean, as well as their growth and metabolism directly or indirectly in numerous ways (Raven 2017, Raven et al. 2020). Many studies have pre- viously reported the response of marine algal growth to temperature warming and elevated CO 2 (Kremp et al. 2012, Tatters et al. 2013, Brandenburg et al. 2019, Seto et al. 2019). In general, global warming benefits algal growth if the increased temperature is below the optimal Received October 3, 2020, Accepted December 8, 2020 *Corresponding Author E-mail: kykim@chonnam.ac.kr Tel: +82-62-530-3465, Fax: +82-62-530-0065 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Com- mercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.