Deep Heat: A Comparison of Water Temperature, Anemone Bleaching, Anemonefish Density and Reproduction between Shallow and Mesophotic Reefs

Round 1

Reviewer 1 Report

This is a very interesting paper on an emerging topic that is well written. The findings are also interesting and some observations made are quite new. The paper is based on some anedoctical observations due to the rare nature of the occurrence of the species of interest at the deeps that were surveyed. In my opinion, this ms deserves to be published, but I have a few suggestions that I think would be needed to be addressed in the production of a revised version. I detail these suggestions below. Overall, I think that this ms could be accepted after major revisions.

 

Comments and suggestions :

Introduction

The main goals of the study are not clearly presented and the relationships with the three criteria presented in lines 37-43 are not evident. Some topics of the Introduction could be further expanded and, in some cases, key facts and figures could also be included in order to put in evidence the relevance and potential impact of this study.

Methods

Although possible according to the authors guidelines of the journal, in my opinion, the inclusion of the Methods as the last section of the paper, does not contrinute to a full understanding of the work done and implies some mixing between the methods and the results sections (for instance, Figure 1 should be in the Methods section toghether with some study area characterization in order to better understand the results obtained. I suggest to change the structure of the paper or to better define which parts are relative to results and those referring to methods. This section should be further expanded, since there are many details in the results and discussion (temperature plots) sections, for which it would be important to have a description on the way results were obtained.

Results

Some measures of observation efforts per area/ or dive are needed. Numbers of orange-fin anemonefish are quite low and the sampling effort was high with more than 350 dives, which highlight its scarcity at the deepth range surveyed. The sampling effort was probably made unevenly during 2016-2021 period both spatially and temporally. This is an important information that should be presented. An effort should be made in order to present results in a more objective and whenever possible quantitative manner, being some results quite descriptive or not supported at all (e.g. lines 101-103).

Figure 3 is not essential and a sentence describing the timing of spawning would be enough.

Conclusions

In my opinion, authors should be more caution in the relationships between MHW and mesophotic communities, due to the scarcity of the data analysed and due to a wide variety of counfounding effects that were not assessed (lines 248-250).

 

Author Response

Reviewer 1

This is a very interesting paper on an emerging topic that is well written. The findings are also interesting and some observations made are quite new. The paper is based on some anecdotal observations due to the rare nature of the occurrence of the species of interest at the deeps that were surveyed. In my opinion, this ms deserves to be published, but I have a few suggestions that I think would be needed to be addressed in the production of a revised version. I detail these suggestions below. Overall, I think that this ms could be accepted after major revisions.

We thank the reviewer for their insightful comments. We have examined the structure of the paper, added more detail in the Introduction adding key facts and making our main goals clearer. We have added density estimates thanks to survey efforts and transects and we have removed superfluous figures. We hope the reviewer is pleased with the outcome.

 

Comments and suggestions :

Introduction

The main goals of the study are not clearly presented and the relationships with the three criteria presented in lines 37-43 are not evident. Some topics of the Introduction could be further expanded and, in some cases, key facts and figures could also be included in order to put in evidence the relevance and potential impact of this study.

We have considerably expanded on the Introduction and added key facts and thanks to this we have more clearly stated our main goals.

 

Methods

Although possible according to the authors guidelines of the journal, in my opinion, the inclusion of the Methods as the last section of the paper, does not contribute to a full understanding of the work done and implies some mixing between the methods and the results sections (for instance, Figure 1 should be in the Methods section together with some study area characterization in order to better understand the results obtained. I suggest to change the structure of the paper or to better define which parts are relative to results and those referring to methods. This section should be further expanded, since there are many details in the results and discussion (temperature plots) sections, for which it would be important to have a description on the way results were obtained.

Unfortunately we cannot change the order of the Methods, but we have now tried to better but briefly describe the methods at the beginning of each of the results section. We have also greatly expanded upon the Methods section.

 

Results

Some measures of observation efforts per area/ or dive are needed. Numbers of orange-fin anemonefish are quite low and the sampling effort was high with more than 350 dives, which highlight its scarcity at the depth range surveyed. The sampling effort was probably made unevenly during 2016-2021 period both spatially and temporally. This is an important information that should be presented.

Thanks to the reviewer we have combined observation efforts per area which has led to the inclusion of density estimates in the paper which we believe greatly improve the paper.

 

An effort should be made in order to present results in a more objective and whenever possible quantitative manner, being some results quite descriptive or not supported at all (e.g. lines 101-103).

We agree and we have now included more quantitative results.

 

Figure 3 is not essential and a sentence describing the timing of spawning would be enough.

We agree and Fig 3 has been removed.

 

Conclusions

In my opinion, authors should be more caution in the relationships between MHW and mesophotic communities, due to the scarcity of the data analysed and due to a wide variety of counfounding effects that were not assessed (lines 248-250).

We agree and we have downplayed the relationship between the two.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Haguenauer and colleagues is a well written report of anemone bleaching at mesophotic depths in French Polynesia. This information is key to understanding the role of these deeper ecosystems in providing a refuge for shallow water populations. The methods are appropriate, but I would like to see one additional piece of information: what proportion of these species live in the mesophotic versus shallow ecosystems? Do you have that information? If a very small percentage lives at depth, the likelihood that they will provide a significant amount of larvae to the shallows is low, especially if threats in the shallows continue.

Finally, one key reference is missing. Rocha et al (2018, Science 361: 281-284) made similar observations and reached a similar conclusion: that mesophotic ecosystems have a limited potential as refuges. This should be cited early in the introduction. As is, the introduction gives the impression that this paper is the first to reach this conclusion, which is not the case.

Author Response

Reviewer 2

The manuscript by Haguenauer and colleagues is a well written report of anemone bleaching at mesophotic depths in French Polynesia. This information is key to understanding the role of these deeper ecosystems in providing a refuge for shallow water populations. The methods are appropriate, but I would like to see one additional piece of information: what proportion of these species live in the mesophotic versus shallow ecosystems? Do you have that information? If a very small percentage lives at depth, the likelihood that they will provide a significant amount of larvae to the shallows is low, especially if threats in the shallows continue.

We thank the reviewer for their comments and we have now compared the proportion of anemonefish between shallow and mesophotic reefs as yes we did have that information. Infact, thanks to these comments we have modified the paper so that we better compare multiple measures between shallow and mesophotic reefs.

 

 

Finally, one key reference is missing. Rocha et al (2018, Science 361: 281-284) made similar observations and reached a similar conclusion: that mesophotic ecosystems have a limited potential as refuges. This should be cited early in the introduction. As is, the introduction gives the impression that this paper is the first to reach this conclusion, which is not the case.

We thank the reviewer for this additional reference, which we now refer to the Introduction.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic of the paper is interesting, that is can coral reefs and associated species living in deeper zones act as refuges and sources for recolonization of reefs in more shallow areas that have been impacted by marine heat waves as a result of anthropogenic climate change? Unfortunately, however, I find that the results are not sufficiently substantial to merit publication. They consist of (few) observational data that seem to have been collected opportunistically. There is nothing inherently wrong with this, but the observations are so few and results so inconclusive that it is difficult to see what substantially new knowledge is presented here. I also find the manuscript to be poorly organized. Detailed comments follow below, in order of occurrence in the manuscript.

1. Title. I appreciate "tongue in cheek" humoristic titles, but to be honest I cannot really see the connection between "How deep is your love" and the contents of the paper.
2. The abstract is rudimentary and does not provide a sufficient overview of the paper. Notably, there is no mentioning of any methods applied, so readers will have to guess how the data were generated.
3. L. 52-56. Given the findings from other species, how novel is the finding of spawning in deeper zones in the present paper?
4. L. 59. investigated -> investigate
5. L. 64-69. If spawning at these depths is so rare, then I would question if your (few) observations of spawning in the mesophotic zone would be of much biological significance, e.g. as contributors to recolonization of shallow zones that have been impacted by marine heat waves. As a whole, I miss a quantitative assessment/ quantitative arguments about the possibility of recolonization (e.g. information about fecundity, recruitment patterns etc.).
6. L. 91-94. A lot of emphasis is put on this single observation of bleaching. How much can really be concluded from this? I am not an expert in corals, but I wondered if bleaching can also occur due to other factors (and if not, this would be worth pointing out).
7. L. 104-111. Based on three observations I do not think much can be concluded about the fit of time of reproduction with lunar cycle (and one of the three clutches does not fit the expected pattern).
8. L. 134-136. Yes, I agree, but again you have very few observations and it would be good with some qualification of the statement, e.g. information about fecundity etc.
9. L. 140-150. Again, you observed only three breeding pairs and 2 of them followed the expected lunar cycle whereas the third did not. I do not think much can be concluded based on this.
10. L. 174-208 including Figs. 4 and 5.. Here you present new results that have not been mentioned before. It becomes quite confusing. These results should have been presented in the results section and better integrated in the general context of the paper.
11. L. 226. The discussion ends abruptly in the middle of a sentence.

In total, I have mixed feelings about the paper. The topic is certainly important, but the study is based on very few observations and is therefore preliminary in nature. I do not think much can be concluded on the basis on this, but if more data could be collected and/or the biological significance of the findings were better substantiated then there would be potential for a useful publication.

 

Author Response

Reviewer 3

 

The topic of the paper is interesting, that is can coral reefs and associated species living in deeper zones act as refuges and sources for recolonization of reefs in more shallow areas that have been impacted by marine heat waves as a result of anthropogenic climate change? Unfortunately, however, I find that the results are not sufficiently substantial to merit publication. They consist of (few) observational data that seem to have been collected opportunistically. There is nothing inherently wrong with this, but the observations are so few and results so inconclusive that it is difficult to see what substantially new knowledge is presented here. I also find the manuscript to be poorly organized. Detailed comments follow below, in order of occurrence in the manuscript.

We thank the reviewer for the critical but pertinent comments. As such we have examined the structure of the paper and moved a lot of material from the Discussion to the results section as well as deleted other parts. We have also transformed our observational data into quantitative measures that have now been compared between shallow and mesophotic reefs. We thank the reviewer as this data always existed but we needed these comments to realise this.

 

1. I appreciate "tongue in cheek" humoristic titles, but to be honest I cannot really see the connection between "How deep is your love" and the contents of the paper.

We hesitated, but due to this comment, coupled with our new data comparing multiple measures between shallow and mesophotic reefs, we have changed the title to better match the paper.

 

2. The abstract is rudimentary and does not provide a sufficient overview of the paper. Notably, there is no mentioning of any methods applied, so readers will have to guess how the data were generated.

We have now changed the Abstract substantially and it should better match the paper now.

 

3. 52-56. Given the findings from other species, how novel is the finding of spawning in deeper zones in the present paper?

To our knowledge, only one paper on fish to date has shown vertical connectivity from mesophotic to shallower zones – and for that reproduction is necessary. Apart from that paper, the reproduction of only one other species, Stegastes, has been in investigated in mesophotic reefs. A such we believe our results are still novel.

 

4. 59. investigated -> investigate

Changed as suggested

 

5. 64-69. If spawning at these depths is so rare, then I would question if your (few) observations of spawning in the mesophotic zone would be of much biological significance, e.g. as contributors to recolonization of shallow zones that have been impacted by marine heat waves. As a whole, I miss a quantitative assessment/ quantitative arguments about the possibility of recolonization (e.g. information about fecundity, recruitment patterns etc.).

We now quantify frequency of spawning at depth with that in shallow areas and find that spawning frequencies are in fact quite similar between these two zones and hence they are biologically significant. As we mention in the discussion it is still an open issue whether larvae from mesophotic couples recruit onto shallow habitats as most, if not all, parentage analysis studies until today did not sample mesophotic individuals. Hopefully this paper will help highlight this bias in future parentage studies.

 

6. 91-94. A lot of emphasis is put on this single observation of bleaching. How much can really be concluded from this? I am not an expert in corals, but I wondered if bleaching can also occur due to other factors (and if not, this would be worth pointing out).

While other factors, such as salinity, dissolved oxygen, light, etc… can also affect corals causing bleaching, thermal stress is largely recognized as the main cause of coral bleaching and the association of high temperature with coral bleaching observed in this study supports this hypothesis. In addition, in French Polynesia bleaching is known to be associated with marine heatwaves (Lesser 2019; Brown 1996)”.

 

7. 104-111. Based on three observations I do not think much can be concluded about the fit of time of reproduction with lunar cycle (and one of the three clutches does not fit the expected pattern).

We agree and we have toned down the discussion on the synchronisation with the lunar cycle and removed the figure.

 

8. 134-136. Yes, I agree, but again you have very few observations and it would be good with some qualification of the statement, e.g. information about fecundity etc.

We are a little unsure as to the question as the line numbers do not seem to match up with the reviewers questions. However if the reviewers refers to fecundity at depth, unfortunately we could not count the eggs as we do normally in shallow waters using ImageJ as the camera lens used at depth was not appropriate for macro photographs.

If we have not answered the question, please do not hesitate to query it again.

 

9. 140-150. Again, you observed only three breeding pairs and 2 of them followed the expected lunar cycle whereas the third did not. I do not think much can be concluded based on this.

We agree and as stated above, we have toned down the synchronisation with lunar cycle part in the publication.

 

10. 174-208 including Figs. 4 and 5.. Here you present new results that have not been mentioned before. It becomes quite confusing. These results should have been presented in the results section and better integrated in the general context of the paper.

We have re-structured the paper and now either the Figure has been removed or moved into the Results section.

 

11. 226. The discussion ends abruptly in the middle of a sentence.

We have modified the discussion now and checked the ending.

 

In total, I have mixed feelings about the paper. The topic is certainly important, but the study is based on very few observations and is therefore preliminary in nature. I do not think much can be concluded on the basis on this, but if more data could be collected and/or the biological significance of the findings were better substantiated then there would be potential for a useful publication.

Thanks to the comments of all the reviewers we have added more data to the paper, better comparing the shallow and mesophotic reefs. The paper is now also better structured and the introduction is more inconclusive and our aim better defined. I hope you will now find it acceptable for publication.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Re: Haguenauer et al. " Deep heat: A comparison of water temperature, anemone bleaching, anemonefish density and reproduction between shallow and mesophotic reefs.

 

I have read through the revised manuscript with great pleasure. Although I was quite critical regarding the initial submission, I do think the authors have done a great job in revising their paper. First of all, the new version is much better written, more logically structured and more coherent. Also, the claims and considerations are now much better substantiated by quantitative arguments, and in cases where conclusions are weakened by limited data this is clearly acknowledged. I therefore recommend acceptance, although I find that the paper would benefit from additional proofreading and improvement of the English.

 

 For instance, l. 68-70 does not read well and the same goes for l. 76-78 (and the whole para for that matter). I think the problem consists in listing assumptions of the deep reef refuge hypothesis. In some cases these are listed as sentences, in others as points, followed by "however...". It becomes quite confusing and should be written in a more consistent manner.

Author Response

We thank the reviewer for their earlier critical comments which we agree helped in significantly improving the manuscript.

We have read through the paper again and improved the English in multiple places. In particular, we have modified the first and second paragraphs, as pointed out, specifically focusing on the list of assumptions. We hope the English has improved sufficiently now.