30 Nov 2022
30 Nov 2022
Status: this preprint is currently under review for the journal BG.

Observed and projected impacts of coastal warming, acidification, and deoxygenation on Pacific oyster (Crassostrea gigas) farming: A case study in the Hinase Area, Okayama Prefecture and Shizugawa Bay, Miyagi Prefecture, Japan

Masahiko Fujii1,2, Ryuji Hamanoue2, Lawrence Patrick Cases Bernardo1, Tsuneo Ono3, Akihiro Dazai4, Shigeyuki Oomoto5, Masahide Wakita6, and Takehiro Tanaka7 Masahiko Fujii et al.
  • 1Faculty of Earth Environmental Science, Hokkaido University, Sapporo, 0600810, Japan
  • 2Graduate School of Environmental Science, Hokkaido University, Sapporo, 0600810, Japan
  • 3National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Yokohama, 2368648, Japan
  • 4Center for Sustainable Society, Minamisanriku, 9860775, Japan
  • 5Eight-Japan Engineering Consultants Inc., Okayama, 7008617, Japan
  • 6Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, Aomori, 0350022, Japan
  • 7NPO Satoumi Research Institute, Okayama, 7048194, Japan

Abstract. Coastal warming, acidification, and deoxygenation are progressing, primarily due to the increase in anthropogenic CO2. Coastal acidification has been reported to have effects that are expected to become more severe as acidification progresses, including inhibiting formation of the shells of calcifying organisms such as shellfish. However, compared to water temperature, an indicator of coastal warming, spatiotemporal variations in acidification and deoxygenation indicators such as pH, aragonite saturation state (Ωarag), and dissolved oxygen in coastal areas of Japan have not been observed and projected. Moreover, many species of shellfish are important fisheries resources, including Pacific oyster (Crassostrea gigas). Therefore, there is concern regarding the future combined impacts of coastal warming, acidification, and deoxygenation on Pacific oyster farming, necessitating evaluation of current and future impacts to facilitate mitigation measures. We deployed continuous monitoring systems for coastal warming, acidification, and deoxygenation in the Hinase area of Okayama Prefecture and Shizugawa Bay in Miyagi Prefecture, Japan. In Hinase, the Ωarag value was often lower than the critical level of acidification for Pacific oyster larvae, although no impact of acidification on larvae was identified by microscopy examination. Oyster larvae are anticipated to be affected more seriously by the combined impacts of coastal warming and acidification, with lower pH and Ωarag values and a prolonged spawning period, which may shorten the oyster shipping period and lower the quality of oysters. No significant future impact of surface-water deoxygenation on Pacific oysters was identified. To minimize the impacts of coastal warming and acidification on Pacific oyster and related local industries, cutting CO2 emissions is mandatory, but adaptation measures such as regulation of freshwater and organic matter inflow from rivers and changes in the form of oyster farming practiced locally might also be required.

Masahiko Fujii et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2022-223', miho ishizu, 02 Dec 2022 reply
  • RC1: 'Comment on bg-2022-223', Anonymous Referee #1, 21 Dec 2022 reply

Masahiko Fujii et al.

Masahiko Fujii et al.


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Short summary
This is the first study of the current and future impacts of climate change on Pacific oyster farming in Japan. Future coastal warming and acidification may affect oyster larvae, as a result of longer exposure to lower pH waters. A prolonged spawning period may harm oyster processing by shortening the shipping period and reducing oyster quality. To minimize impacts on Pacific oyster farming, in addition to mitigation measures, local adaptation measures may be required.