The Água Clara Cave System in Northeastern Brazil: The Richest Hotspot of Subterranean Biodiversity in South America

Round 1

Reviewer 1 Report

This paper provides biodiversity information on an important cave system in Brazil, and it is very appropriate for the special issue of diversity. While I don't have any issue with the overall content (i.e. no major revisions required), there are numerous minor issues that the authors should address before the manuscript is accepted. Of particularly concer are issues 1, 6-8, 9, 12, 16-18.

1. English language and clarity issues (see details below).

2. For many cavers, the term 'cave system' refers to a single continuously traversable cave with multiple entrances. The authors use the term to refer to multiple, hydrologically connected but not contiguous caves. I suggest considering the term 'cave complex' or explicitly stating at first use that the term refers to multiple caves.

3. lines 43-49: Neither the IUCN redlist nor the term HSB safeguards species in any way, they just highlight which species or areas are in greatest need. I suggest rewording this sentence.

4. lines 88-90: Consider providing more information about how the boundaries of speleological regions are delineated: it wasn't too clear.

5. Section 1 Introduction: A little more on Brazil-specific conservation of subterranean resources is warranted here.

6. Fig. 1: The image is too low resolution and the text is much too small. Especially the legends in panes D and E are illegible even when zoomed way in.

7. Fig. 1: In pane B, there is a large karst area in the northeast corner: why isn't it numbered as a speleological region?

8. Fig 2: Cave maps would be nice if available. What's the yellow box in pane A? Why do 'some entrances of the Lapa dos Peixes cave' get a curvy yellow arrow when the others caves get white straight arrrows? Text in pane 1 is too small.

9. Sections 2-5 are all about the geology and hydrology of the system. This is not a hydrogeo journal. These sections seem way too long, going on for several pages, especially considering that sections 6-7 on the biological data are only 2 short paragraphs taking up less than half a page. Those sections should be expanded since this is a biology journal. Also, a huge chunk of section 5 (lines 251 - 288) have no citations but provide a lot of information on cave geomorphology.

10. Throughout all of the discussion of the hydrology of the section, I never got an answer to a most basic question: Do the multiple caves in the system represent a single flowpath or multiple drainages?

11. Line 306-307: 'at least 10 visits'. Why can't the authors provide a firm number on how many times the cave/s were visited?

12. I am skeptical or at least surprised by two taxa on their list: Nylanderia sp. and Mesodiplatys. Moldovan et al., 2018 state that globally there is only 1 possible troglobiont so to state that this one is as well is an extraordinary claim that, in my opinion, requires extraordinary explanation, especially considering that the species isn't identified to species. In the Mesodiplatys description, the authors call it only a potential troglobiont, citing elongated appendages, but also acknowledging it's unusually large eyes and dark pigmentation. Perhaps these taxa should atleast be discussed under notable species and defended more strongly or their designation be amended to 'potential troglobionts'.

13. Lines 341-344: I would like to see more explanation of the methods employed by Souza-Silva et al., and some clarification on how the conclusion of an adequate level of sampling completeness was determined. 78% is not that high.

14. Lines 357-361: I would like to see more explanation/ defense of this hypothesis that the size of the cave passage is driving diversity. It isn't a hypothesis that I'm familiar with. Indeed, in my experience, large passages in the tropics are often drier and contain more troglophiles. Perhaps the authors are referring to the length of passages or overall habitat extend, particularly of mesocaverns? There is a good body of literature on that subject as a driver of biodiversity.

15. In all of section 7 there is no discussion of aquatic habitats or aquatic species.

16. Section 8.3: I think this discussion of the value of the magic number is interesting, but I think it could benefit from some rewording and additional development. There are growing examples of high-diversity spots in arid areas (like parts of Australia) so I think that the tropic - vs temperate comparison is an incomplete picture. Also in lines 490-501 the authors argue that Culver and Sket did not take into account level of threat or large-scale differences in biodiversity patterns, but that was never the point of the 20 species or subsequent 25 species cutoff. Culver and Sket were always more interested in the biogeographic question of why some areas have more or fewer troglobionts, but they never argued the 20 or 25 species was a cutoff for conservation value! On another topic, I think the authors could improve this section by providing citations for alternative approaches to identifying hotspots (e.g. identifying hotspots at regional levels versus global levels or identifying natural breaks in datasets). I agree with the authors that the 25 species threshold is arbitrary, but they could use this opportunity to cite more useful alternatives.

17. Lines 518 - 550. The authors site IDH as a driver of biodiversity but I don't think the argument is especially strong. They say that flood pulses can be classified as intermediate disturbance, but how do they come to that conclusion. Most of their examples in this section suggest niche-partitioning and habitat diversity as drivers, but the link between niche separation and IDH isn't very strong to me or even conflated.

18. Lines 560-573: Again the authors potentially conflate two separate mechanisms: they begin by talking about the size of cave systems, but then most of this paragraph is about environmental history of the region. Those are two different mechanisms driving diversity or if not, the link isn't defined clearly.

19. Line 575: What does 'official' mean in this sentence?

20. Table 2: Why are collembola species numbers not chronological? I.e. 1, 2, 4, 7?

21. Table 2: Spiripockia has a remarkable morphology. Surely this is a noteable species. Also, Pulmonata I don't think is currently recognized as a valid taxon.

The English is generally quite good and usually easy to understand. However, throughout the document there are minor wording issues like better word options, areas where fewer words would be better, passive voice, and phrasings that seem confusing or at least distracting. The paper could benefit from careful editing by a native speaker perhaps. There were more of these than I could keep track of.

The biggest areas where I struggled to understand the authors meaning were:

Lines 64-67

Line 151-152 (unique karst implications and non-karstifiable coverings)

Line 164-166

Lines 194-197

Line 206

Line 266-270 (I think this section can be shortened and resolved by introducing the term 'floodwater maze'.

Line 376 (morphologic, genetic differences or both?)

Line 458-459

Line 569: I think refugia vs refuge might be more appropriate here?

Author Response

Comments and Suggestions for Authors

This paper provides biodiversity information on an important cave system in Brazil, and it is very appropriate for the special issue of diversity. While I don't have any issue with the overall content (i.e. no major revisions required), there are numerous minor issues that the authors should address before the manuscript is accepted. Of particularly concern are issues 1, 6-8, 9, 12, 16-18.

1. English language and clarity issues (see details below).
2. We made an effort to enhance the language, particularly in the areas you highlighted in your review. We sincerely appreciate your valuable suggestions.
3. For many cavers, the term 'cave system' refers to a single continuously traversable cave with multiple entrances. The authors use the term to refer to multiple, hydrologically connected but not contiguous caves. I suggest considering the term 'cave complex' or explicitly stating at first use that the term refers to multiple caves.
4. The term "Cave system" typically refers to a grouping of caves that are interconnected through accessible passages or linked hydrologically, or it can describe a cave with a vast network of chambers and passages. In this particular context, we are specifically referring to the hydrological connection among the caves. Therefore, we prefer to maintain the term "Cave system."
5. lines 43-49: Neither the IUCN redlist nor the term HSB safeguards species in any way, they just highlight which species or areas are in greatest need. I suggest rewording this sentence.
6. OK. Corrected in the text.
7. lines 88-90: Consider providing more information about how the boundaries of speleological regions are delineated: it wasn't too clear.
8. OK. Corrected in the text.
9. Section 1 Introduction: A little more on Brazil-specific conservation of subterranean resources is warranted here.
10. We added a paragraph on this subject as suggested.
11. Fig. 1: The image is too low resolution and the text is much too small. Especially the legends in panes D and E are illegible even when zoomed way in.
12. The figure was rearranged.
13. Fig. 1: In pane B, there is a large karst area in the northeast corner: why isn't it numbered as a speleological region?
14. The figure was rearranged
15. Fig 2: Cave maps would be nice if available. What's the yellow box in pane A? Why do 'some entrances of the Lapa dos Peixes cave' get a curvy yellow arrow when the others caves get white straight arrrows? Text in pane 1 is too small.
16. The figure was rearranged and corrected.
17. Sections 2-5 are all about the geology and hydrology of the system. This is not a hydrogeo journal. These sections seem way too long, going on for several pages, especially considering that sections 6-7 on the biological data are only 2 short paragraphs taking up less than half a page. Those sections should be expanded since this is a biology journal. Also, a huge chunk of section 5 (lines 251 - 288) have no citations but provide a lot of information on cave geomorphology.
18. We sincerely appreciate your observations and suggestions. We have incorporated additional information on the biology, which aligns with the manuscript's primary focus. However, considering the lack of a compiled literature focused on the regional and local geology of the Serra do Ramalho area, we believe it is crucial to retain this characterization of the geological and hydrological settings. This information holds potential significance for numerous readers.
19. Throughout all of the discussion of the hydrology of the section, I never got an answer to a most basic question: Do the multiple caves in the system represent a single flowpath or multiple drainages?
20. A flow path traverses all the caves within the system; however, this flow path can receive water from various small tributaries originating from different sources such as epikarst, among others.
21. Line 306-307: 'at least 10 visits'. Why can't the authors provide a firm number on how many times the cave/s were visited?
22. We changed it on the text. There were 10 visits to the cave system.
23. I am skeptical or at least surprised by two taxa on their list: Nylanderia sp. and Mesodiplatys. Moldovan et al., 2018 state that globally there is only 1 possible troglobiont so to state that this one is as well is an extraordinary claim that, in my opinion, requires extraordinary explanation, especially considering that the species isn't identified to species. In the Mesodiplatys description, the authors call it only a potential troglobiont, citing elongated appendages, but also acknowledging it's unusually large eyes and dark pigmentation. Perhaps these taxa should atleast be discussed under notable species and defended more strongly or their designation be amended to 'potential troglobionts'.
24. We highly value your observations. As a result, we have included further information in the text regarding these two species, specifically addressing their troglobitic status and providing arguments in support of our findings.
25. Lines 341-344: I would like to see more explanation of the methods employed by Souza-Silva et al., and some clarification on how the conclusion of an adequate level of sampling completeness was determined. 78% is not that high.
26. We added a reference indicating some estimates of sampling completeness: Ávila A.C., Pires M.M., Rodrigues E.N., Costi J.A., Stenert C., Maltchik L. Drivers of the beta diversity of spider assemblages in southern Brazilian temporary wetlands. Ecol Entomol. 2019, 45(3):466–475. https://doi. org/ 10. 1111/ een. 12816
27. Lines 357-361: I would like to see more explanation/ defense of this hypothesis that the size of the cave passage is driving diversity. It isn't a hypothesis that I'm familiar with. Indeed, in my experience, large passages in the tropics are often drier and contain more troglophiles. Perhaps the authors are referring to the length of passages or overall habitat extend, particularly of mesocaverns? There is a good body of literature on that subject as a driver of biodiversity.
28. Indeed, we proposed that the voluminous chambers and conduits within the ACCS might play a role in the development of highly troglomorphic (hypogeomorphic) species, such as harvestmen, whip spiders, and springtails. As mentioned earlier in the text, the presence of extensive underground voids suggests that these species would need to cover significant distances in their search for food or potential mates. Consequently, individuals could potentially benefit from possessing longer and more sensitive appendages, aiding both in sensory perception and locomotion. This hypothesis aligns with the findings of Trontelj et al. (2012), highlighting the importance of pore size in the evolutionary process of cave organisms.
29. In all of section 7 there is no discussion of aquatic habitats or aquatic species.
30. We genuinely appreciate your observation regarding this matter. Regrettably, we inadvertently overlooked highlighting the importance of these particular species and habitats. However, we have considered your suggestion and included a new paragraph dedicated to discussing this subject in greater detail.
31. Section 8.3: I think this discussion of the value of the magic number is interesting, but I think it could benefit from some rewording and additional development. There are growing examples of high-diversity spots in arid areas (like parts of Australia) so I think that the tropic - vs temperate comparison is an incomplete picture. Also in lines 490-501 the authors argue that Culver and Sket did not take into account level of threat or large-scale differences in biodiversity patterns, but that was never the point of the 20 species or subsequent 25 species cutoff. Culver and Sket were always more interested in the biogeographic question of why some areas have more or fewer troglobionts, but they never argued the 20 or 25 species was a cutoff for conservation value! On another topic, I think the authors could improve this section by providing citations for alternative approaches to identifying hotspots (e.g. identifying hotspots at regional levels versus global levels or identifying natural breaks in datasets). I agree with the authors that the 25 species threshold is arbitrary, but they could use this opportunity to cite more useful alternatives.
32. We sincerely appreciate your observation. We added a discussion presenting other possibilities, as you have suggested.
33. Lines 518 - 550. The authors site IDH as a driver of biodiversity but I don't think the argument is especially strong. They say that flood pulses can be classified as intermediate disturbance, but how do they come to that conclusion. Most of their examples in this section suggest niche-partitioning and habitat diversity as drivers, but the link between niche separation and IDH isn't very strong to me or even conflated.
34. We genuinely appreciate your observation regarding this matter. However, we maintain our confidence in the interpretation that the flood pulses represent intermediate disturbances, as detailed in the text where we provide a thorough explanation of our conclusion.
35. Lines 560-573: Again the authors potentially conflate two separate mechanisms: they begin by talking about the size of cave systems, but then most of this paragraph is about environmental history of the region. Those are two different mechanisms driving diversity or if not, the link isn't defined clearly.
36. We sincerely appreciate your observation. We have corrected this paragraph, as you have suggested.
37. Line 575: What does 'official' mean in this sentence?
38. We removed the term “oficially”
39. Table 2: Why are collembola species numbers not chronological? I.e. 1, 2, 4, 7?
40. I must admit that I did not fully comprehend your question…
41. Table 2: Spiripockia has a remarkable morphology. Surely this is a noteable species. Also, Pulmonata I don't think is currently recognized as a valid taxon.
42. We sincerely appreciate your observation. We have corrected this, changing “Pulmonata” by “Eupulmonata”.

Comments on the Quality of English Language

The English is generally quite good and usually easy to understand. However, throughout the document there are minor wording issues like better word options, areas where fewer words would be better, passive voice, and phrasings that seem confusing or at least distracting. The paper could benefit from careful editing by a native speaker perhaps. There were more of these than I could keep track of. The biggest areas where I struggled to understand the authors meaning were:

Lines 64-67

Line 151-152 (unique karst implications and non-karstifiable coverings)

Line 164-166

Lines 194-197

Line 206

Line 266-270 (I think this section can be shortened and resolved by introducing the term 'floodwater maze'.

Line 376 (morphologic, genetic differences or both?)

Line 458-459

1. We genuinely appreciate your observation. We have diligently worked towards improving the language, specifically focusing on the areas you highlighted earlier.

Line 569: I think refugia vs refuge might be more appropriate here?

1. Changed as suggested.

Author Response File: Author Response.docx

Reviewer 2 Report

This is a fine paper on the richness of the Brazilian caves.
Apart from some minor comments and corrections that authors may find in the PDF file, I have no major complaints and think that the minor revision is sufficient.

All the best,

Comments for author File: Comments.pdf

Author Response

Thank you immensely for your valuable comments and observations, which have undoubtedly enhanced the manuscript. We have implemented most of your suggestions throughout the text, aiming to meet the high-quality standards you expect. Regarding your suggestion to include the author and year of description for each troglobitic species, we have decided to incorporate the references of the original descriptions. This choice allows readers to access the primary sources for further exploration and examination. Once again, we express our gratitude for your input.

Author Response File: Author Response.docx

Reviewer 3 Report

General Comments

The work is very interesting, it is well planned, the tables are adequated, the references are appropriate and the figures and photographs are of quality and are informative.  The part about Regional Geology, Hydrogeology and Local karst I cannot judge objectively since I lack sufficient knowledge in this discipline and I do not have updated information on Brazil.

The final part that refers to the Brazilian legislation on the conservation of caves and the threats faced by karstic ecosystems in the study area adds value to the work. It is necessary to show the fragility of the subterranean environment and try to make the society aware of the importance of biodiversity in caves so that they can actively participate in its conservation.

Some specific comments:

1. The sampling methods are not detailed, nor when or how they have been carried out in the at least 10 visits mentioned ( “at least 10 visits conducted in total” )... Please expand this information.

2. It is a pity that the recent faunal captures have been preserved in 70% ethanol and not in 95% ethanol that would allow DNA to be extracted from the material later… I advise authors to use pure alcohol with a look to the future.

3. Based on the data, it seems that little is known about the stygobiont fauna, and regarding the troglobiont fauna, you have estimated the level of sampling effort, and I think you should also include a note on the sampling effort carried out in the aquatic environment, even if it was a small effort... to try to understand the scarcity of stygobionts.

4. The authorship of all genera and species must be given the first time they are cited in the text, this is mandatory and thus you avoid having to cite them in "References".

5. Page 11, line 375. Is there any work that justifies the statement: “… Serra do Ramalho area, may comprise cryptic species complexes.”? Please references!!.

6. Page 12, line 412. Change Table 1 to Table 2.

I hope to be able to read this work published soon

All the best

Author Response

The work is very interesting, it is well planned, the tables are adequated, the references are appropriate and the figures and photographs are of quality and are informative.  The part about Regional Geology, Hydrogeology and Local karst I cannot judge objectively since I lack sufficient knowledge in this discipline and I do not have updated information on Brazil.

The final part that refers to the Brazilian legislation on the conservation of caves and the threats faced by karstic ecosystems in the study area adds value to the work. It is necessary to show the fragility of the subterranean environment and try to make the society aware of the importance of biodiversity in caves so that they can actively participate in its conservation.

Thank you immensely for your valuable comments and observations, which have undoubtedly enhanced the manuscript. We have implemented most of your suggestions throughout the text, aiming to meet the high-quality standards you expect.

Some specific comments:

1. The sampling methods are not detailed, nor when or how they have been carried out in the at least 10 visits mentioned (“at least 10 visits conducted in total” )... Please expand this information. R. We changed it on the text. There were 10 visits to the cave system.
2. It is a pity that the recent faunal captures have been preserved in 70% ethanol and not in 95% ethanol that would allow DNA to be extracted from the material later… I advise authors to use pure alcohol with a look to the future. R. Thank you for your suggestion. We will consider it in our future field works.
3. Based on the data, it seems that little is known about the stygobiont fauna, and regarding the troglobiont fauna, you have estimated the level of sampling effort, and I think you should also include a note on the sampling effort carried out in the aquatic environment, even if it was a small effort... to try to understand the scarcity of stygobionts. R. We genuinely appreciate your observation regarding this matter. Regrettably, we inadvertently overlooked highlighting the importance of the aquatic species. However, we have considered your suggestion and included a new paragraph dedicated to discussing this subject in detail.
4. The authorship of all genera and species must be given the first time they are cited in the text, this is mandatory and thus you avoid having to cite them in "References". R. We fully acknowledge your observation regarding this matter. Nonetheless, we have made the decision to incorporate the references of the original descriptions, rather than including the author and year of description for each troglobitic species. This approach enables readers to directly access the primary sources of description, facilitating further exploration and examination.
5. Page 11, line 375. Is there any work that justifies the statement: “… Serra do Ramalho area, may comprise cryptic species complexes.”? Please references!!. R. Indeed, the aforementioned observations stem from ongoing research conducted by our team, resulting in the absence of published articles on this subject at the present time.
6. Page 12, line 412. Change Table 1 to Table 2. R. Changed.

I hope to be able to read this work published soon

Thank you so much!!!!

All the best

Author Response File: Author Response.docx