Biodiversity and Environmental Factors Structuring Diatom Assemblages of Mineral Saline Springs in the French Massif Central

Round 1

Reviewer 1 Report

Dear Author

This is a well-designed study. The data collected was fully analysed and easy to read.  The obtained results have certain significance regarding biodiversity and environmental factors structuring diatom assemblages of mineral saline springs in the French Massif Central.

The abstract should include 1 or 2 more sentences about the research method.

"The main aim of our project was to evaluate the biodiversity of seventy-nine mineral saline springs situated in the French Massif Central and the influence of environmental factors in order to have a better knowledge of the ecology of the observed diatom species" is too general for this study. Please specialize the hypothesis question for this study. 

 

In the introduction, the authors talk too much about the environmental conditions of a hot spring. But the connection between hot springs and diatoms is too short "In mineral springs, these microalgae are studied by diatomists all over the world (e.g. [21-26])". It is difficult for the reader to accept this statement. Please provide a detailed review of the bio-diversity of diatom in hot springs.

Tables 1-2-3 can be combined.

The results on diatom diversity are pale compared to the results of too in-depth an analysis of environmental factors.

The author wrote, "Overall, 307 different species were observed. The diatom community of the studied saline springs in the French Massif Central shares many species with other thermal springs in Europe such as Poland [24] and Italy [59,67] and also in other parts of the world such as Chile [68]. Some rare species were observed such as Pseudostaurosira cubonii described from a spring in Italia (Sicilia) [69]." Authors should analyse and list diatoms shared in common among these similar ecosystems (preferably having a supplementary list of over 300 identified diatom species).

Best wishes

Author Response

Many thans for all the comments. It will improve the MS. 

All comments were taken into account. 

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a neat, in depth study of the benthic diatom communities found seventy-nine (79) mineral saline springs situated in the French Massif Central region.  This study is valuable. Springs are abundant but endangered and diatom biofilms are important components of these ecosystem services, but their species composition is less well understood. The authors are among the few groups with the expertise to be able to combine detailed species work of a relatively ill-studied and specific diatom flora with wider ecological and environmental considerations.

The English is far from perfect but the manuscript in this current form is quite readable and clear. It could benefit of a more thorough proof reading by the authors to correct minor errors.

Nonetheless it is an overall well-written paper. The introduction is adequate and the methods and chosen data analyses are sound. The result are clear and complete and discussion is satisfactory.

My own major quibble is the usage of the term “observed richness”. Why no stick with the well-know and widespread used “species richness, S” if both terms simply refer to number of species per sample?

I do recommend the publication of the paper.

Minor comments below:

Line 34 – include a small definition of “crenal”. It is an obscure term

Line 86 – the main aim of the paper is not very clear in this paragraph

Line 98 – “departments” – this term is not obvious for the readers unfamiliar of French administrative organization.

Line 149 - reference for piper diagrams

Line 169 – Confusing. Please clarify. Is Species richness (i.e number of species, S) to be used interchangeably with Chao1 index? Why? They are not the same thing.

Line 176 – if you log-transformed the species abundance data how did you down-weighted rare species? Log-transformation is a severe transformation, but it does not down-weights the abundance of rare species. Please clarify.

Line 182 – Reference for MRPP analysis

Line 203 – Figure 2 impossible to discern the orange diamond and very difficult to see blue diamond and pink diamond.

Line 233 – ACP’s group 1 and 2 are not delimited in figure 2. Do both include all samples?

Line 258 – So, species richness (named “observed richness”) and Chao1 were both measured. In fact, most results (e.g Figs 4; Figs 10; table 7) are for “observed richness”. This term is also somewhat confusing to the reader. Given it represents the number of species why not uses the more widespread term “species richness, S”.

Line 317 – Please include the legend of the used OMNIDIA codes in Figure 9.

Line 423 – 426 these are results already mentioned in lines 275-288. Redundant paragraph.

Line 513 – low diversity in springs with man-made structures is not discussed. Any thoughts on the subject?

Author Response

Many thans for all the comments. It will improve the MS. All comments were taken into accounts.

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of the manuscript (diversity-2203791) titled:

Biodiversity and environmental factors structuring diatom assemblages of mineral saline springs in the French Massif Central

 I have some questions and recommendations:

1. Line 86 – The aim of this study is to show the biodiversity – all groups of organisms …? I suggest redrafting the aim of the research presented in this manuscript.

2. Why do the authors in the introduction not cite their work from BIOM, 2020: Biodiversity and ecology of diatoms in mineral springs of the area of Sainte Marguerite (Saint-Maurice-es-Allier, Massif central, France) as preliminary research from this area?

3. From the description in Materials and methods it follows that the samples in particular springs (all 79) was taken only a one-time, is it true? For how many years were the samples collected, because from the description of the methods I only got information that since December 2014.

4. I suggest adding a column in table S1 with information on the dominant type of substrate from which samples were taken in individual springs. The type of substrate determines the presence of specific species.

5. Line 141 - there is Naphrax, and it should be Naphrax®

6. What are the reasons for assuming that species with a relative abundance of more than 1% are dominant? In diatom ecology, depending on the ecosystem (flowing or stagnant waters), we use more than 5% or even 10% relative abundance.

7. The Piper diagram does not clearly show the colors used in the description of the obtained results, especially the orange diamond is not visible.

8. I believe that the plates with photos of dominant species are not necessary in this work. They contain only pictures taken in SEM, and it is worth to include an illustration from LM and SEM with such documentation. However, one of the dominant species, Crenotia angustior, is missing from the plates. Also in Fig. 8, Nitszchia communis is illustrated by photos c and d, not a and b, while a and b are Nitzschia valdecostata.

9. Planothidium frequentissimum is considered a cosmopolitan species with a wide range of tolerance to environmental conditions, occurring in large numbers in many types of ecosystems. Therefore, it is difficult to consider it as an indicator of specific features of the environment, except for extreme conditions. As the authors themselves pointed out, its occurrence is limited by water temperature and currently they indicate high level of mineralization.

Author Response

Many thans for all the comments. It will improve the MS. All comments were taken into accounts.

Author Response File: Author Response.pdf