Spatio-Temporal Dynamics of Larval Fish Assemblage in the Nakdong River Estuary, South Korea

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a very interesting and meaningful basic research. Several relatively straightforward and repeatable experimental methods have obtained many interesting results, which are highly suitable for publication in this journal. Here are some suggestions for revisions for the authors to consider:

Line 79: Due to the seasonal division's regional-specific nature, the authors should clarify this classification and provide relevant literature.

Lines 88-90: It is suggested that the authors revise this paragraph to: "From April 2013 to December 2015, bi-monthly field sampling was conducted at 10 stations in the Nakdong River estuary, including three stations in the inner estuary (A1–A3) and seven stations in the outer estuary (B1–B7) (Fig. 1)."

Line 117: It is suggested that the authors provide further explanation on the significance of selecting two different mesh sizes (300 and 200 μm) for collecting fish and zooplankton. The authors seem to have mentioned it slightly, but it is unclear.

Line 167: Since I am unable to understand some sources of variables (SST, SSS, and others), it is recommended that the authors provide clarification at an appropriate point in the article.

Line 173: Some of the textual descriptions in this paragraph remain focused on the materials and methods. The authors should clarify the definitions of variables (SST, SSS, BWT, and others) in the preceding section.

Line 186: For Figure 2, it is recommended that the authors avoid abbreviations as much as possible in the Y-axis labels and ensure consistency with the rest of the article.

Author Response

Reviewer #1

Comments and Suggestions for Authors

This is a very interesting and meaningful basic research. Several relatively straightforward and repeatable experimental methods have obtained many interesting results, which are highly suitable for publication in this journal. Here are some suggestions for revisions for the authors to consider:

 

Line 79: Due to the seasonal division's regional-specific nature, the authors should clarify this classification and provide relevant literature.

(Response) We added relevant literature for classifying two seasons (i.e., Park et al., [2020]).

 

Lines 88-90: It is suggested that the authors revise this paragraph to: "From April 2013 to December 2015, bi-monthly field sampling was conducted at 10 stations in the Nakdong River estuary, including three stations in the inner estuary (A1–A3) and seven stations in the outer estuary (B1–B7) (Fig. 1)."

(Response) We revised this sentence as suggested.

 

Line 117: It is suggested that the authors provide further explanation on the significance of selecting two different mesh sizes (300 and 200 μm) for collecting fish and zooplankton. The authors seem to have mentioned it slightly, but it is unclear.

(Response) According to reviewer #2 comment, we removed the description for zooplankton samples. Thus, only 300 μm net was used for collecting larval fish samples.

 

Line 167: Since I am unable to understand some sources of variables (SST, SSS, and others), it is recommended that the authors provide clarification at an appropriate point in the article.

(Response) We added a description indicating all hydrological parameters as well as their acronyms, i.e., sea surface temperature (SST), bottom water temperature (BWT), sea surface salinity (SSS) and bottom water salinity (BWS) in the first paragraph of “2.1. Sampling and laboratory procedures” section.

 

Line 173: Some of the textual descriptions in this paragraph remain focused on the materials and methods. The authors should clarify the definitions of variables (SST, SSS, BWT, and others) in the preceding section.

(Response) Again. We added a description indicating all acronyms of hydrological parameters n the first paragraph of “2.1. Sampling and laboratory procedures” section.

 

Line 186: For Figure 2, it is recommended that the authors avoid abbreviations as much as possible in the Y-axis labels and ensure consistency with the rest of the article.

(Response) Due to the limitation of height in Y-axis, we used abbreviations for all hydrological parameters. Instead, we added a caption describing SST, BWT, SSS and BWS. These abbreviations were used consistently in the rest of the text.

Reviewer 2 Report

Comments and Suggestions for Authors

Spatio-temporal dynamics of larval fish assemblage in the Nakdong River estuary, Korea

This study investigated the spatiotemporal patterns of the species composition and abundance of larval fish assemblages in a Korean river, in the inner and outer estuaries. In general, is a well-written manuscript with an interesting topic. However, I have detected some flaws that need to be addressed before I can recommend this paper for publication.

A first observation is that the authors should give a background on why they specifically studied those years (2013-2015), considering that from 2013 the initial decrease in freshwater discharge was observed, as a consequence of the dams.  Therefore the studied years are similar in that respect. Besides this, the authors state that there is a limited understanding of how the structures of larval fish assemblages change in response to environmental changes in estuarine habitats in Korea, but considering that the study was undertaken after the dams were constructed, it is not clear how can they demonstrate this change. In this sense, the authors must indicate the importance of those years within the context of this study.

 

Secondly, in the Results section, many results were not properly described in the M&M section. Figures 2 and 3 are not properly described. Section 3.4 was not defined either in the M&M section or as one of the goals of this work. None of this section was previously introduced.

 

Finally, the discussion is too long, and it repeats many results. Authors should first clearly define the scope of the paper, and then discuss accordingly. For instance, nothing else is mentioned about the zooplankton after its mention at the beginning of the M&M section.

Minor comments

Section 3.3. Why did the authors not perform a richness test?

On line 91, the authors state that hydrological parameters were recorded, such as temperature and depth. They need to describe all the parameters that were taken.

Line 115. The collection and study of zooplankton samples seems to be out of the scope of this work. My recommendation is to leave this out, but if authors decide to leave it, they need to clearly state this in the introduction, and adequately define the scope of this work.

Line 124. Why was the Shannon index was used? Did the assumptions of this index were met?

 

Line 147. The DistLM needs the construction of two matrixes, one for the environmental data and another for the biota. Authors need to describe how they build these matrixes.

Line 269. Did the authors not perform a marginal test in DistLM? What was the selection criterion they used?

 

Figure 5 Sal_a, Sal_b, Temp_S, temp_ B need to be explained in the caption. 

Comments on the Quality of English Language

Although my first language is not English, I consider that the overall MS would benefit from an English editing service.

Author Response

Reviewer #2

Comments and Suggestions for Authors

Spatio-temporal dynamics of larval fish assemblage in the Nakdong River estuary, Korea

 

This study investigated the spatiotemporal patterns of the species composition and abundance of larval fish assemblages in a Korean river, in the inner and outer estuaries. In general, is a well-written manuscript with an interesting topic. However, I have detected some flaws that need to be addressed before I can recommend this paper for publication.

 

A first observation is that the authors should give a background on why they specifically studied those years (2013-2015), considering that from 2013 the initial decrease in freshwater discharge was observed, as a consequence of the dams. Therefore the studied years are similar in that respect. Besides this, the authors state that there is a limited understanding of how the structures of larval fish assemblages change in response to environmental changes in estuarine habitats in Korea, but considering that the study was undertaken after the dams were constructed, it is not clear how can they demonstrate this change. In this sense, the authors must indicate the importance of those years within the context of this study.

(Response) We added some description on how construction of estuary barrages influences on estuary ecosystems in the third and fourth paragraphs of Introduction section. There have been similar research on larval fish assemblages between the pre- (1987-1988) and the post-period (2013-2015) of construction of estuary barrages, and we found major changes in dominant species. We revised the “4.4. Influences of estuary barrage on fish larvae” section by reflecting those information.

 

Secondly, in the Results section, many results were not properly described in the M&M section. Figures 2 and 3 are not properly described. Section 3.4 was not defined either in the M&M section or as one of the goals of this work. None of this section was previously introduced.

(Response) We added descriptions of methods that were not properly described in the Result section. The modified M&M section included the explanations about Figure 2 and 3, and section 3.4 (figure 4).

 

Finally, the discussion is too long, and it repeats many results. Authors should first clearly define the scope of the paper, and then discuss accordingly. For instance, nothing else is mentioned about the zooplankton after its mention at the beginning of the M&M section.

(Response) We revised the overall discussion section according to the reviewer’s comments. We first removed or modified repeated descriptions of the results, and then focused on clearly defining scope of this paper. The method and result of zooplankton analysis was also removed through the text.

 

Minor comments

 

Section 3.3. Why did the authors not perform a richness test?

(Response) We considered the number of species (or species number) as species richness. The species richness, abundance and diversity were tested using three-way ANOVA.

 

On line 91, the authors state that hydrological parameters were recorded, such as temperature and depth. They need to describe all the parameters that were taken.

(Response) We added a description indicating all hydrological parameters as well as their acronyms, i.e., sea surface temperature (SST), bottom water temperature (BWT), sea surface salinity (SSS) and bottom water salinity (BWS) in this paragraph.

 

Line 115. The collection and study of zooplankton samples seems to be out of the scope of this work. My recommendation is to leave this out, but if authors decide to leave it, they need to clearly state this in the introduction, and adequately define the scope of this work.

(Response) We removed the description for zooplankton samples as suggested.

 

Line 124. Why was the Shannon index was used? Did the assumptions of this index were met?

(Response) We added a description of Shannon index assumptions. According to Shannon’s assumption, our samplings are well met in using the index.

 

Line 147. The DistLM needs the construction of two matrixes, one for the environmental data and another for the biota. Authors need to describe how they build these matrixes.

(Response) We constructed DistLM based on a matrix of the biota and added overlay vectors of environmental variables. I think it looks good to link species abundance to environmental variables. Several previous papers also used DistLM to measure the relationship between biological assemblage and environmental variables (see below).

 

Chen, K. S., Chen, H. S., Chen, C. Y., Su, Y. L., Meng, P. J., & Chen, M. H. (2022). Multivariate analysis of the spatial species diversity of demersal fish assemblages in relation to habitat characteristics in a subtropical national park, Taiwan. Marine Biodiversity, 52(1), 4.

 

Wellington, C. M., Harvey, E. S., Wakefield, C. B., Abdo, D., & Newman, S. J. (2021). Latitude, depth and environmental variables influence deepwater fish assemblages off Western Australia. Journal of Experimental Marine Biology and Ecology, 539, 151539.

 

Line 269. Did the authors not perform a marginal test in DistLM? What was the selection criterion they used?

(Response) We already added the results of DistLM marginal test in the second paragraph of “3. Assemblage structure of larval fish”. We used Akaike Information Criterion (AIC) for DistLM, and this information was already in the third paragraph of “2.2 Data analysis”.

 

Figure 5 Sal_a, Sal_b, Temp_S, temp_ B need to be explained in the caption.

(Response) We added a description indicating all hydrological parameters, i.e., sea surface temperature (SST), bottom water temperature (BWT), sea surface salinity (SSS) and bottom water salinity (BWS) in the Figure 5 caption.

 

Comments on the Quality of English Language

Although my first language is not English, I consider that the overall MS would benefit from an English editing service.

(Response) We already edited the language from the English editing company (https://www.editage.com/) before original submission. Due to limitation of resubmission deadline, we will conduct additional language editing before the resubmission of next round revision.

Reviewer 3 Report

Comments and Suggestions for Authors

The paper investigated the spatial and temporal variation in species composition and abundance of a 55-species larval fish taxa in the estuary. The research method and results are sound.

1.The acronym needs to be clearly stated, is it related to the name of the survey station, or the fish taxon? E.g., Gobiidae sp.A and Gobiidae sp.H.

2.This abstract section needs to be revised to present the main results. Delete the descriptive sentences in the results section. Research conclusions or significance need to be added.

3.Line 17: Delete “(April 2013 to December 2015)”.

4.The research and review of literature in the introduction section is inadequate.

5.Line 71: “Although several studies have been conducted on the distribution of ichthyoplankton in Korean waters, only a few studies have investigated the distribution of ichthyoplankton in estuarine environments [21–24].” needs to be modified. The literature collected and read is not enough.

6.Poor articulation of Line 74 and Line 75. In addition, the motivation and significance of the study were not clear and unambiguous.

7.Figure 1: Need to add a global map in the top left corner.

8.Figures 2 and 3: Year & Month, Year & Season, add a space.

9.Table 2: P italicized; The F-statistic?

10.Figure 4: Solid points need to be transparent. The number of spatio-temporal dynamic maps is different for these four dominant species.

11.Line 258: global R = 0.038 is R-squared or R^2 = 0.038?

12.Line 260: P italicized.

13.Line 272: P-values <0.05 ? Add “-”.

14.Add subheadings to the discussion section.

15.The conclusion section adds the limitations of the study.

Author Response

Reviewer #3

The paper investigated the spatial and temporal variation in species composition and abundance of a 55-species larval fish taxa in the estuary. The research method and results are sound.

 

1. The acronym needs to be clearly stated, is it related to the name of the survey station, or the fish taxon? E.g., Gobiidae sp.A and Gobiidae sp.H.

(Response) We changed “Gobiidae sp.A, sp.B and sp.H” into “Gobiidae sp.1, sp.2 and sp.8” using numerical order to avoid any confusion with the name of the survey station.

 

2. This abstract section needs to be revised to present the main results. Delete the descriptive sentences in the results section. Research conclusions or significance need to be added.

(Response) We clearly described the abstract section by modifying descriptive sentences. We also revised the sentences to state the research conclusions clearly.

 

3. Line 17: Delete “(April 2013 to December 2015)”.

(Response) We removed “(April 2013 to December 2015)” from the sentence.

 

4. The research and review of literature in the introduction section is inadequate.

(Response) We reviewed more literature and revised the overall introduction accordingly.

 

5. Line 71: “Although several studies have been conducted on the distribution of ichthyoplankton in Korean waters, only a few studies have investigated the distribution of ichthyoplankton in estuarine environments [21–24].” needs to be modified. The literature collected and read is not enough.

(Response) By reviewing more literature, we added some descriptions of the influences of estuary barrages on fish assemblages in this paragraph.

 

6. Poor articulation of Line 74 and Line 75. In addition, the motivation and significance of the study were not clear and unambiguous.

(Response) We revised the poor articulation in Line 74 and 75. The motivation and significance of this study are to identify seasonal occurrence patterns and spatial distributional patterns of common fish larvae in the study area. We are clarifying this point in the last paragraph of introduction section.

 

7. Figure 1: Need to add a global map in the top left corner.

(Response) We added a global map in the top left corner as suggested.

 

8. Figures 2 and 3: Year & Month, Year & Season, add a space.

(Response) We added a space between “Year”, “&” and “Month” as suggested.

 

9. Table 2: P italicized; The F-statistic?

(Response) We italicized “P”, but not for “F”.

 

10. Figure 4: Solid points need to be transparent. The number of spatio-temporal dynamic maps is different for these four dominant species.

(Response) We changed the solid points to be transparent. The spatio-temporal dynamic maps were shown when each species occurred, thus the number of maps is different depending on species.

 

11. Line 258: global R = 0.038 is R-squared or R^2 = 0.038?

(Response) “global R” indicates ANOSIM statistic that is different with R^2.

 

12. Line 260: P italicized.

(Response) We revised all “P” in italic.

 

13. Line 272: P-values <0.05 ? Add “-”.

(Response) We added hyphen as suggested.

 

14. Add subheadings to the discussion section.

(Response) We added the subheadings for the paragraphs of the discussion section

 

15 .The conclusion section adds the limitations of the study.

(Response) We already added the limitations of the study in the original submission as follows: “However, owing to the lack of information regarding the impact of environmental variables on biological communities in the Nakdong River estuary, further studies are needed to determine how fluctuations in freshwater discharge can affect the ecosystem of the Nakdong River estuary through continuous monitoring”.