the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
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
- 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
- 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)
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CC1: 'Comment on bg-2022-223', miho ishizu, 02 Dec 2022
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Major comments
This study mentioned about the development of continuous monitoring systems for coastal warming, acidification and deoxygenation in the local areas in Japan by observation and modeling. In addition, they try to project the future situation under the IPCC scenario.
Reading through this manuscript, I thought that the volumes of each section are unbalanced. Especially, the volume for the result section is too short, compared to the volumes of introductions and methods.
I believe that one of the highlights in this study is to develop the model for the specific coastal area. Therefore it would be better to add more analysis by using the model outputs to show how their model is reproduced well in this target coastal area. At that time, seasonal horizontal distributions of each variable could be useful with comparison of the other observational data. Probably DIC and ALK are probably difficult to be got horizontally, but temperature and salinity, oxygen data could be available if you try to find in Japan. These improvements could make you deepen for your understanding of the model, which will make useful for your future study.
Minor comments
Abstract:
The sentence of the abstract should be blushed up. The current abstract was not a self-contained summary of your work. Method, how to examine and what you found should be included. The sentence “Coastal warming, acidification, … to facilitate mitigation measures” can be shorten. The sentence “To minimize… oyster farming practiced locally might also be required” is not necessary.
Title:
After revising the manuscript, I suggest you reconsider the title. The current title does not reflect the content of the current manuscript.
1. Introduction:
The sentences are too long. The sentence can be shorter. The current manuscript is divided into 5 sections (1.1, ~ 1.5), but I think it would be better to write it all in one. When you improve the manuscript, you also think about the balance of the volumes in the section. The volume of the introduction is heavy compared to the results, discussion and conclusion sections.
2.1 Study sites:
This section is also too heavy, compared to the results, discussion and conclusion sections.
3.1 Observed results:
The current version has been divided the section into 3.1.1~3.l.7, but you don’t need to divide individually. Please reconsider this part.
3.2 Modeling results:
The results of the numerical models are necessary. Please put additional analysis such as horizontal distributions and so on to show how the model reproduces in this target area horizontally and timely.
Section 3.2.2 Future projection:
This section is a discussion matter. This part can be moved to the discussion section if you add analyses of the model reproducibility.
Section 4.2:
The section 4.2, 4.2.1 and 4.2.2 can be moved to the conclusion section. Please reconsider your construction.
Please add references after the sentence (Extreme events such as severe…intensely in the future) in page 16.
5. Conclusion:
The conclusion should be improved. Basic conclusion includes the purpose, the summary of this study and self-evaluation/prospects.
Fig 1:
The information of latitude and longitudes are necessary. Right figures are not appropriate in scientific papers. I think that making an original map by yourself is necessary. In that case, Japanese character should not be included in your map. Right figure is relatively too small.
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RC1: 'Comment on bg-2022-223', Anonymous Referee #1, 21 Dec 2022
reply
General comments
This manuscript by Fujii et al. submitted to Biogeoscience deals with current and future habitat for Pacific oyster (Crassostrea gigas) in two coastal sites in Japan. Recent reports that acidification has already negatively impacted on oyster growth along the West Coast of the United States are widely known among researchers. Also in Japan, the economic impact should be very large since oysters are a representative marine product. As such, the suggestion that the reduction of anthropogenic CO2 can largely alter future habitat for oyster will be impressive for not only scientific community, but also for the general public.
Another commendable point of this paper is a successful long-term monitoring in coastal sites with several sensors. The figures presented in the manuscript suggest that the quality of data obtained by the sensors was good. As far as I know, there are not so much cases of such successful long-term monitoring in coastal sites. These observations should be maintained in the future.
My largest concern about this manuscript is the absence of long-term warming under RCP8.5 at Hinase. It is too unrealistic that future warming at Hinase is almost negligible (Figure 13a). There was no mention about future physical environment in the Seto Inland Sea in Nishikawa et al. [2021], which cited in the text. So, I could not verify whether negligible warming in this region is true or not. However, air temperature will likely increase over the long term under RCP8.5. It is difficult to believe that rising in air temperature will not affect water temperatures in the shallow Seto Inland Sea. I strongly urge the authors to check water temperature projections in the Seto Inland Sea.
Negligible warming in Hinase has resulted in much of the discussion being focused on whether or not there is an increase in water temperature. The differences in expected spawning period between Hinase and Shizuagawa appear to be due to the presence or absence of long-term warming. As this manuscript covered two cites, I want the authors to discuss the relationship between regional characteristics and expected changes in habitat for oysters. For example, Hinase is more enclosed area than Shizukawa. Do these differences in characteristics have any effect on acidification in the future? Unfortunately, there is little discussion about the impact of factors other than water temperature on environmental change at current manuscript.
Also, I think long-term oligotorophication in the Seto Inland Sea is a hot topic. I recommend that the authors mention regarding oligotorophication. If it is impossible, the author should mention as limitation of the projection in the text.
I agree with the posted comment (by Dr. Ishizu) that discussion is too little in the current manuscript. The authors have competent observational data and computational methods. Further discussions utilizing these resources are needed for the acceptance.
Specific comments
(Line 164) The reference about oligotrophication (i.e., an overcome of eutrophication) is needed. I think that Abo and Yamamoto [2019], which was already cited in the text is suitable.
(Line 207) Information about the calibration of DO sensor is needed. I suppose that it was done by two-point calibration at 0% and 100%.
(Line 237) “The maximum error ~ is about 10 μmol kg-1” Is this true? In Figure 2, some TA data appear to be deviated by more than 10 μmol kg-1 from possible regression line.
(Line 305) “Although no significant differences were observed among the sites in Hinase, salinity was generally higher at H-4 than at the other three sites throughout the year.” What do these sentences mean? Was the difference in salinity statistically insignificant? The author should clarify whether this difference is important in this study or not.
(Line 313) Does the upper limit of optimal DO range (269 μmol kg-1) have any biological meaning? Most of observed DO exceeded this value (Fig. 4).
(Line 341) “In Shizugawa, the Ωarag value was below the threshold ~. However, no morphological abnormalities were observed ~.” Then, what does the threshold mean?
(Line 438) “Extreme events such as severe storms are anticipated to occur more frequently and intensely in the future.” References are essential.
Masahiko Fujii et al.
Masahiko Fujii et al.
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