Responses of branching reef corals Acropora digitifera and Montipora digitata to elevated temperature and pCO2

Cristiana Manullang; Intan Herwindra Millyaningrum; Akira Iguchi; Aika Miyagi; Yasuaki Tanaka; Yukihiro Nojiri; Kazuhiko Sakai

doi:10.7717/peerj.10562

Responses of branching reef corals Acropora digitifera and Montipora digitata to elevated temperature and pCO₂

PeerJ. 2020 Dec 21:8:e10562. doi: 10.7717/peerj.10562. eCollection 2020.

Authors

Cristiana Manullang¹, Intan Herwindra Millyaningrum¹, Akira Iguchi², Aika Miyagi³, Yasuaki Tanaka⁴, Yukihiro Nojiri^{5

6}, Kazuhiko Sakai⁷

Affiliations

¹ Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, Japan.
² Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
³ Department of Bioresources Engineering, National Institute of Technology, Okinawa College, Nago-City, Okinawa, Japan.
⁴ Environmental and Life Sciences, Universiti Brunei Darussalam, Brunei Darussalam.
⁵ Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan.
⁶ Graduate School of Earth and Environmental Sciences, Hirosaki University, Hirosaki, Aomori, Japan.
⁷ Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Motobu, Okinawa, Japan.

Abstract

Anthropogenic emission of CO₂ into the atmosphere has been increasing exponentially, causing ocean acidification (OA) and ocean warming (OW). The "business-as-usual" scenario predicts that the atmospheric concentration of CO₂ may exceed 1,000 µatm and seawater temperature may increase by up to 3 °C by the end of the 21^st century. Increases in OA and OW may negatively affect the growth and survival of reef corals. In the present study, we separately examined the effects of OW and OA on the corals Acropora digitifera and Montipora digitata, which are dominant coral species occurring along the Ryukyu Archipelago, Japan, at three temperatures (28 °C, 30 °C, and 32 °C) and following four pCO₂ treatments (400, 600, 800, and 1,000 µatm) in aquarium experiments. In the OW experiment, the calcification rate (p = 0.02), endosymbiont density, and maximum photosynthetic efficiency (Fv/Fm) (both p < 0.0001) decreased significantly at the highest temperature (32 °C) compared to those at the lower temperatures (28 °C and 30 °C) in both species. In the OA experiment, the calcification rate decreased significantly as pCO₂ increased (p < 0.0001), whereas endosymbiont density, chlorophyll content, and Fv/Fm were not affected. The calcification rate of A. digitifera showed greater decreases from 30 °C to 32 °C than that of M. digitata. The calcification of the two species responded differently to OW and OA. These results suggest that A. digitifera is more sensitive to OW than M. digitata, whereas M. digitata is more sensitive to OA. Thus, differences in the sensitivity of the two coral species to OW and OA might be attributed to differences in the endosymbiont species and high calcification rates, respectively.

Keywords: Calcification rate; Corals; Endosymbiont species; Ocean acidification; Ocean warming.

Grants and funding

This work was supported by the Japan Society for the Promotion of Science (KAKENHI Nos. 26220102 and 19H00953), the Environment Research and Technology Development Fund (JPMEERF20194007) of the Environmental Restoration and Conservation Agency of Japan, and University of the Ryukyus President’s Research Award for Leading Scientists (no specific grant number). There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.