The Spatio-Temporal Distribution of the Freshwater Bivalves Corbicula fluminea and Dreissena polymorpha in the Lower Sector of the Danube River and the Danube Delta

Round 1

Reviewer 1 Report

This study took lots of time cost and field work, but the presentation of their work is not good. The authors didn't distinguish the importance and innovation of their studies from other similar studies, and they didn't perform enough analysis and show important findings. I suggest the authors add more environmental factors and more analysis, show the dynamic changes of distribution of two species, update the distribution of two species and dig more important and interesting results, to get more important conclusions rather than citing lots of previous studies in the discussion.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We kindly thank you for reviewing the paper and we really appreciate the comments and recommendations. Indeed, the paper was intended to be a review of the historical records and invasion pathways of the two species but also to bring new and original data on the spreading of the two species along the Danube River, based on a timeseries data set that covers a period of 10 years long. Moreover, the study contains information on the demographic structure of the populations of the two species, which is a novelty among this kind of studies. Indeed, while a comprehensive review of ecological requirements of the two species based on the literature records was performed, we faced some limitations concerning the availability of some essential environmental parameters when we analysed our own data. So, we’ve decided to stick with the best available data (particle size of sediment and TOC concentrations) of the institute under which umbrella we’ve performed my study. The dynamic of the two species along the Danube has been shown in two dimensions: at temporal and spatial scales. Original data on multiannual abundances and demographic structure of their populations as well as a description of their extent in the same periods were provided.

Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for inviting me to review this paper. I immensely enjoyed it. The study is the result of extensive surveys of the Danube for the invasive zebra mussel, D. polymorpha, and the Asian clam, C. fluminea. The authors also undertook a comprehensive review of the biogeography of the two species, bioinvasive capabilities, and their effects on the benthic communities. The study was well-planned, executed, analyzed, and presented.  The references used are appropriate, and the paper flows well. The global review adds an essential component to the paper allowing the reader to comprehend the complexity of bioinvasions and the human footprint.

Author Response

Dear reviewer,

We kindly thank you for reviewing the paper and we really appreciate the comments.

Reviewer 3 Report

Thank you for the opportunity to read this interesting article. The study of the spread of invasive species is undoubtedly an urgent scientific problem, since the settlement of alien plants and animals constitutes a serious threat to sustainable development. The authors have studied in sufficient detail the distribution and abundance of invasive mollusks in the Danube. The choice of methods seems to be quite reasonable, although, of course, it is better to involve divers for a more accurate study of bottom microorganisms. But the use of a Van Veen dredger is also a suitable method. It is necessary to indicate in the article the volume of the dredger that was used. The reliability of the data obtained is beyond doubt.

The minor disadvantages of the article include the fact that the authors, indicating in lines 247-248 the locations with the maximum abundance of species in 2010, do not comment on what the subsequent decrease in this indicator could be due to.

In addition, it is possible to slightly shorten the descriptions of the biological features of species, since even non-specialists in malacology are well acquainted with such widespread alien species. When describing areas, it is better to use the names of objects of physical geography, rather than the names of countries.

The article can be published after minor revision

Author Response

Dear reviewer,

We would like to thank you for reviewing our manuscript and for your constructive comments and suggestions. We have addressed your comments carefully and made the corresponding changes in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Author Response

Dear Reviewer,

We kindly thank you for reviewing the paper and we really appreciate the comments and recommendations. Indeed, the paper was intended to be a review of the historical records and invasion pathways of the two species but also to bring new and original data on the spreading of the two species along the Danube River, based on a timeseries data set that covers a period of 10 years long. Moreover, the study contains information on the demographic structure of the populations of the two species, which is a novelty among this kind of studies. Indeed, while a comprehensive review of ecological requirements of the two species based on the literature records was performed, we faced some limitations concerning the availability of some essential environmental parameters when we analysed our own data. So, we’ve decided to stick with the best available data (particle size of sediment and TOC concentrations) of the institute under which umbrella we’ve performed my study. The dynamic of the two species along the Danube has been shown in two dimensions: at temporal and spatial scales. Original data on multiannual abundances and demographic structure of their populations as well as a description of their extent in the same periods were provided.

Author Response File: Author Response.pdf