Identification of Phytoplankton-Based Production of the Clam Corbicula japonica in a Low-Turbidity Temperate Estuary Using Fatty Acid and Stable Isotope Analyses
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsGeneral comments
Corbicula japonica is an important organism in the estuarine ecosystems, capable of removing large amounts of suspended matter from the estuary and it is a valuable bio-detector. It is also an important fishery resource due to its high secondary production. Therefore, much attention has been paid to its trophic ecology by the academic community.
While traditional analytical methods such as long-term direct observation in the field are time-consuming and labor-intensive to study, the biochemical tracer method is an efficient way to obtain information on the diet of target organisms over time by reflecting the assimilation of food sources in their tissues. Stable isotopes and fatty acids were chosen for the study as indicators for analysis. Carbon isotope ratio (d 13C) values of animal tissues reflect those of their diet and determine the carbon source of the animal. The nitrogen isotope ratio (d 15N) was used as a proxy for the nutritional status of the animal. FA enables the transfer of nutrients from producer to consumer to be tracked, distinguishing dietary fat from non-dietary fat. Thus, the above analysis leads to a reasonable determination of the trophic basis of the food web of the estuarine ecosystem.
The manuscript uses CTD to obtain water temperature and salinity data, and C. japonica was collected by sieving. Two collection sites for C. japonica and one downstream river site were selected as water sampling sites for isotopic and fatty acid (FA) measurements. It is scientifically valid to compare the differences between different sources at the same site. Elemental composition of C and N and FA biomarkers were analyzed using an elemental analyzer to distinguish between allochthonous and autochthonous food sources. The effects of clam size, salinity gradient and season were investigated to determine its resource use pattern in the low turbidity temperate Seomjin River estuary in Korea. The results suggest that C. japonica production under unique low turbidity estuarine conditions is heavily dependent on phytoplankton-derived organic matter, with river- and marsh-derived particulate matter playing only a minor role. Thus, the manuscript's study of the unique environmental and trophic characteristics of the Seomjin River estuary helped to characterize the food web of the low turbidity estuary in this region. Consequently, the manuscript can be accepted after major revisions.
Other problems are listed in detail as below
1. The manuscript only describes the characteristics of the estuarine food web and lacks reflections and suggestions for ecosystem restoration. Please add relevant content.
2. Line 362: Here is only a brief description of the image. Please add a description of the image.
3. Line 159: It is the membrane that should be dried after the SPM measurement and not the filter used for the SPM measurement. Please clarify the formulation of the filter membrane.
4. Figure 5: The year and month are not clearly labelled in the chart, causing ambiguity in understanding. Please clearly indicate the year.
5. Line11 and Line72: A technical abbreviation appearing at the first time should be marked with the full name.
6. Line24: Please standardize the keywords font.
7. Line 36 and Line 37: Delete the use of redundant dummy words, e.g. hence, therefore.
8. Table 1, Table 2, Table 4, Table S3, Table S4: Please mark the top corner with the information.
9. Table 3: Please add separators for numbers over 1000.
10. Line 192, Line 193, Line 200, Line 201: Please leave a space between the value and the unit.
Author Response
1. The manuscript only describes the characteristics of the estuarine food web and lacks reflections and suggestions for ecosystem restoration. Please add relevant content.
RESPONS: Thanks and agree. According to the reviewer’s suggestion, we have added some description relevant to ecosystem restoration. We have moved some descriptions of the ‘5. Conclusions’ section to last paragraph of the ‘4. Discussion’ section, as suggested by the reviewer #2, and combined discussion contents of interspecific competition with suggestions for ecosystem restoration. (see Lines 555-565 in the revised ms)
2. Line 362: Here is only a brief description of the image. Please add a description of the image.
RESPONSE: Thanks and agree. In this section, we explained a clear separation in FA compositions of E-SPOM, R-SPOM, and P. australis. Then we described the association in the FA profiles between food sources (i.e., E-SPOM, R-SPOM, and P. australis) and C. japonica on the nMDS plot (Figure 4) (see Lines 383-393). According to the reviewer’s comment, we have added more details explaining FAs contributing to this separation as follows: “This separation was attributed to close correlations of E-SPOM with w3:w6 ratio, C22:6w3, C20:4w6, and C20:5w3, and R-SPOM and P. australis with C22:0, C18:2w6, and C18:0”. (see Lines 364-366 in the revised ms)
3. Line 159: It is the membrane that should be dried after the SPM measurement and not the filter used for the SPM measurement. Please clarify the formulation of the filter membrane.
RESPONS: Thanks and agree. Accordingly, we have revised to clarify SPM measurement as follows: “Filters containing SPM were dried at 60°C for 72 h and the SPM mass was computed from the weight difference before and after filtration”. (see Lines 157-159 in the revised ms)
4. Figure 5: The year and month are not clearly labelled in the chart, causing ambiguity in understanding. Please clearly indicate the year.
RESPONSE: Thanks for checking and comment. As suggested by the reviewer, we have added “year” for all components in the revised figure. (see Figure 5 in the revised ms)
5. Line11 and Line72: A technical abbreviation appearing at the first time should be marked with the full name.
RESPONSE: Thanks. We made a mistake. Accordingly, we have revised “SIs” to “stable isotopes (SIs)”. (see Line 71 in the revised ms)
6. Line 24: Please standardize the keywords font.
RESPONSE: Thanks. We have fitted the font style and size in the revised version accordingly.
7. Line 36 and Line 37: Delete the use of redundant dummy words, e.g. hence, therefore.
RESPONSE: Agree. We have deleted “hence” and “therefore” in the revised ms accordingly
8. Table 1, Table 2, Table 4, Table S3, Table S4: Please mark the top corner with the information.
RESPONSE: Thanks for comment. This is likely to be an editorial issue.
9. Table 3: Please add separators for numbers over 1000.
RESPONSE: Agree. We have revised all in ‘Table 3’ accordingly.
10. Line 192, Line 193, Line 200, Line 201: Please leave a space between the value and the unit.
RESPONSE: Thanks for checking typo. We have revised according to the reviewer’s comment. (see Lines 199-200 in the revised ms)
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript investigates food resources of the clam C. japonica in the estuary of Seomjin River based on SI and FA analyses. It is a well conducted and clearly presented study. For that reason, I have only very few minor comments.
Page 3, chapter 2.1, 2nd paragraph: Please explain why SI of food sources should change and not overlap any more in non-monsoon seasons as this seems to be the reason for sampling during these periods.
Table 1: This table is a little bit unclear. Please explain why some values are assigned to site 1 or 2 and some are not. If they are not, it is important to know, where they are derived from.
Chapter 3.3: Though it probably does not matter in terms of dietal differences, as the graphs in figure 3 show strong similarities between SI values of all age classes, I doubt that size group formation, in a way where size groups overlap in such a wide range as here, makes sense. Why not make classes as displayed in figure 3 in 5 mm steps, i.e. 0-5, 5-10 etc.?
Author Response
1) Page 3, chapter 2.1, 2nd paragraph: Please explain why SI of food sources should change and not overlap any more in non-monsoon seasons as this seems to be the reason for sampling during these periods.
RESPONSE: We explained seasonal and site effects on SI values of putative food sources as well as compositional disparity in their FAs in the 'Results' (see Table 1) and 'Discussion' sections (see '4.1. Origin of suspended particulate organic matter').
2) Table 1: This table is a little bit unclear. Please explain why some values are assigned to site 1 or 2 and some are not. If they are not, it is important to know, where they are derived from.
RESPONSE: This was based on the results of statistical testing (see P (within source) values in Table 1). When there was no significant difference between sites or seasons, we averaged the values.
3) Chapter 3.3: Though it probably does not matter in terms of dietal differences, as the graphs in figure 3 show strong similarities between SI values of all age classes, I doubt that size group formation, in a way where size groups overlap in such a wide range as here, makes sense. Why not make classes as displayed in figure 3 in 5 mm steps, i.e. 0-5, 5-10 etc.?
RESPONSE: We tried to show the variations in SI values according to (original) size of Cobicula, not by size groups.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe proposed research of this species, as well as the other species of the genus Corbicula, are very important for their treatment as invading species such as Corbicula fluminea.
Author Response
No specific comments here.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have revised according to my suggestions and hopefully the manuscript is suggested to be accepted.
Author Response
No comments here.
