Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper Long-Term Responses of Crustacean Zooplankton to Hydrological Alterations in the Danube Inland Delta: Patterns of Biotic Homogenization and Differentiation by Beracko et al. is truly a significant and valuable contribution to the overall understanding of the ecology of freshwater crustaceans. In this review I have no specific comments, just some general remarks on the manuscript. The introduction section is very long and needs to be shortened considerably as now it looks more like an introduction to a review article than a research paper. Here the authors need to introduce the reader to the main topic of the paper, but instead the authors elaborate on things like Joint Danube Survey, explanation of alpha and beta diversity, metacommunity, functional traits etc., which the audience reading this paper is already familiar with. The materials and methods and the results sections are the biggest negative points of the paper. The large number of statistical methods described here, which are then presented in the results, make the work confusing. The data summarised in nine figures and seven tables with too many statistical tests performed, may lead to spurious findings. I understand that there is a lot of data to present, yet that is always a challenge when dealing with long-term data sets. I like the soundness of the main hypotheses, the way the authors have grouped the sites and categorised the microcrustaceans into different groups. However, I am convinced that the authors' hypotheses can be tested with less analyses. Finally, I suggest reorganising the discussion section after clarifying the data presented.

Author Response

Reviewer comment: The paper Long-Term Responses of Crustacean Zooplankton to Hydrological Alterations in the Danube Inland Delta: Patterns of Biotic Homogenization and Differentiation by Beracko et al. is truly a significant and valuable contribution to the overall understanding of the ecology of freshwater crustaceans. In this review I have no specific comments, just some general remarks on the manuscript. The introduction section is very long and needs to be shortened considerably as now it looks more like an introduction to a review article than a research paper. Here the authors need to introduce the reader to the main topic of the paper, but instead the authors elaborate on things like Joint Danube Survey, explanation of alpha and beta diversity, metacommunity, functional traits etc., which the audience reading this paper is already familiar with. The materials and methods and the results sections are the biggest negative points of the paper. The large number of statistical methods described here, which are then presented in the results, make the work confusing. The data summarised in nine figures and seven tables with too many statistical tests performed, may lead to spurious findings. I understand that there is a lot of data to present, yet that is always a challenge when dealing with long-term data sets. I like the soundness of the main hypotheses, the way the authors have grouped the sites and categorised the microcrustaceans into different groups. However, I am convinced that the authors' hypotheses can be tested with less analyses. Finally, I suggest reorganising the discussion section after clarifying the data presented.

Author response: We appreciate the reviewer’s constructive remark. Following this suggestion as well as the requirements of other reviewers, the introduction was substantially revised and supplemented. Background information not essential to the research context (e.g., information about the Joint Danube Survey, detailed explanations of metacommunity theory, alpha and beta diversity) was either removed or significantly condensed. The revised version now focuses more directly on the study objectives, the ecological relevance of hydrological alterations in the Danube inland delta, and the specific research questions addressed in this paper.

Author response: We respectfully acknowledge the reviewer’s concern but would like to clarify our position. We believe that all the statistical analyses used in this study are relevant and fully support the statements made in the Results and Conclusions. In our view, the methods are described in sufficient detail and clarity in the Materials and Methods section to allow reproducibility and transparency. Moreover, some tables and figures are intended for the Appendix to provide additional support for the results rather than being central to the main text, helping to keep the main narrative focused. We are confident that the chosen presentation balances the need for comprehensiveness with readability, especially given the complexity and long-term nature of the dataset.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The alterations in hydrological environments is an important environmental factor affecting the community of planktonic crustaceans. In this paper, the authors analyzed the spatio-temporal dynamics of planktonic crustacean communities after the operation of the hydroelectric power plant, and tested the hypothesis that hydrological alterations in the Danube riverscape have led to increasing taxonomic and functional homogenization within sites, accompanied by growing differentiation between sites over the past three decades. The authors clearly characterized the spatiotemporal changes of planktonic crustacean using long-term series data. Thus, this paper is worth publishing. But some parts of the papers need reorganization and revision. The main comments is as followed.

1. Need revision. At the beginning, it should be explained why this research was conducted. The author proposed a hypothesis without briefly explaining how it was proposed, and did not respond to the proposed hypothesis at the end of the abstract.
2. Introduction: L34-92. This paragraph is sluggish. I suggested that the authors explained the relevant content more concisely and clearly.
3. The authors should focus on the impact of hydrological conditions on planktonic crustacean.
4. Introduction: L158-177. In this paragraph, the author did not clearly explain why such a hypothesis was proposed, and the objectives were not well distinguished from previous extensive studies.
5. I suggest that the authors should reorganize this part.
6. About the homogenization and differentiation, the authors did not discuss it well as a whole, and most parts focused on specific species.
7. Hydrological changes are important factors affecting planktonic crustacean communities, but other environmental factors can also affect their communities. If there are relevant data on other environmental factors in the literature, please provide appropriate supplementary discussions.
8. Discussion: P540-564. In order to illustrate species richness, there is unnecessary to spend so much space to explain, just list relevant literature to do it.
9. Discussion: P584-586. Why “These species …… upper parapotamal sites” led to “the taxonomic homogenisation of the community of these biotopes”?

 

Other comments:

• Check the expression of scientific names. For example, L350-354, Muller should be Müller.
• In Table A2. For Copepoda, I suggest that the authors list the species as calanoida, copepod and Harpacticoida. For Cladocera, the authors list the species as tychoplanktonic and euplanktonic species. If possible, the authors added the trait information using abbreviation.

Author Response

The alterations in hydrological environments is an important environmental factor affecting the community of planktonic crustaceans. In this paper, the authors analyzed the spatio-temporal dynamics of planktonic crustacean communities after the operation of the hydroelectric power plant, and tested the hypothesis that hydrological alterations in the Danube riverscape have led to increasing taxonomic and functional homogenization within sites, accompanied by growing differentiation between sites over the past three decades. The authors clearly characterized the spatiotemporal changes of planktonic crustacean using long-term series data. Thus, this paper is worth publishing. But some parts of the papers need reorganization and revision. The main comments is as followed.

Need revision:

Reviewer comment: At the beginning, it should be explained why this research was conducted. The author proposed a hypothesis without briefly explaining how it was proposed, and did not respond to the proposed hypothesis at the end of the abstract.

Author response: We thank the reviewer for this valuable suggestion. Added a brief explanation of the research background and the motivation for conducting this study. Clarified how the hypothesis was formulated, based on existing literature. Explicitly stated whether the hypothesis was supported or not at the end of the abstract (lines 27–32).

Reviewer comment: Introduction: L34-92. This paragraph is sluggish. I suggested that the authors explained the relevant content more concisely and clearly. The authors should focus on the impact of hydrological conditions on planktonic crustacean.

Author response: We have carefully revised the indicated paragraph (L34–92) to improve clarity and conciseness. In the revised version, we shortened background details and placed stronger emphasis on the impact of hydrological conditions on planktonic crustaceans. This restructuring highlights the ecological relevance of hydrological variability to Copepoda and Cladocera, while avoiding unnecessary details. The newly added and reorganized text can be found in lines 39–62 and 111–122. We believe these changes make the introduction more focused and better aligned with the reviewer’s suggestion.

Reviewer comment: Introduction: L158-177. In this paragraph, the author does not clearly explain why such a hypothesis was proposed, and the objectives are not well distinguished from those of previous extensive studies. I suggest that the authors should reorganize this part.

Author response: We have reorganized the paragraph (lines 158–177) to more clearly justify the proposed hypothesis. Specifically, we now explain how the hypothesis arises from identified knowledge gaps in previous studies and from the unique hydrological context of our study system. In addition, we have revised the section on research objectives to clearly distinguish them from those addressed in earlier works. These revisions highlight the novelty of our study and provide a stronger rationale for the hypothesis. The newly added text can be found in lines 139–152.

Reviewer comment: About the homogenization and differentiation, the authors did not discuss it well as a whole, and most parts focused on specific species.

Author response: We appreciate this valuable comment. In the revised version, we expanded the discussion on homogenization and differentiation at the community level. Specifically, we now emphasize how hydrological connectivity, dispersal limitation, and local environmental filters jointly shape patterns of taxonomic and functional homogenization within sites and differentiation among sites. To strengthen this section, we also integrated relevant literature from other floodplain systems. The newly added text can be found in lines 610–626. We believe this addition clarifies the mechanisms driving the observed patterns and addresses the reviewer’s concern.

Reviewer comment:  Hydrological changes are important factors affecting planktonic crustacean communities, but other environmental factors can also affect their communities. If there are relevant data on other environmental factors in the literature, please provide appropriate supplementary discussions.

Author response: We fully agree that, in addition to hydrological changes, other environmental factors play a significant role in shaping planktonic crustacean communities. In the revised discussion (lines 627–640), we added a section addressing the influence of other environmental factors, which are frequently reported as important drivers of zooplankton dynamics in floodplain ecosystems. These variables can mediate both taxonomic composition and functional structure, often interacting with hydrological conditions. By including these aspects, we believe the discussion now provides a more comprehensive view of the environmental determinants influencing crustacean zooplankton.

Reviewer comment: Discussion: P540-564. In order to illustrate species richness, there is unnecessary to spend so much space to explain, just list relevant literature to do it.

Author response: We shortened the section on species richness and now illustrate it more concisely by listing relevant literature (lines 525–536).

Reviewer comment: Discussion: P584-586. Why “These species …… upper parapotamal sites” led to “the taxonomic homogenisation of the community of these biotopes”?

Author response: We revised the text to better explain the underlying mechanism. The dominance of a few widespread and tolerant species in the upper parapotamal sites reduced the relative contribution of less common and more habitat-specific taxa.

 

Other comments:

Reviewer comment:  Check the expression of scientific names. For example, L350-354, Muller should be Müller.

Author response: We corrected “Muller” to “Müller” and carefully checked the entire manuscript for consistency in the expression of scientific and author names.

Reviewer comment: In Table A2. For Copepoda, I suggest that the authors list the species as calanoida, copepod and Harpacticoida. For Cladocera, the authors list the species as tychoplanktonic and euplanktonic species. If possible, the authors added the trait information using abbreviation.

Author response: We accept all the proposed changes and will revise Table A2 accordingly by classifying Copepoda and Cladocera as requested. In addition, we have added a database with the categorization of species traits for the identified taxa.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors The authors have answered and justified the changes made. After revision, the manuscript is much improved, so I propose to accept it in its present form.