Novel Interaction between a Rabbitfish and Black Corals

Round 1

Reviewer 1 Report

The authors documented and describe a series of observations a novel interactions between rabbit fish and black corals. After the observatios, the authors propose the hypothesis that Siganus javus on the Yongala are feeding on epibiotic algae or biofilms deposited on the antipatharians’ polyps and/or the zooplankton that the polyp had trapped but not yet indigested. Also, the authors propose that to confirm the hypothesis it is necessary to carry out gut content and morphological analys. I found the manuscript interesting and well written. I consider that this work is a good contribution to the field, however, I have few comments about some details in the text:

 

1. Line 65-66: Are you referring to figure 1a of this manuscript or to that of Malcolm et al., 1999? please clarify.

2. Line 94: Figures 2c,d do not exist, are you referring to figures 1c,d? change please.

Author Response

Reviewer 1

 

The authors documented and described a series of observations a novel interactions between rabbit fish and black corals. After the observations, the authors propose the hypothesis that Siganus javus on the Yongala are feeding on epibiotic algae or biofilms deposited on the antipatharians’ polyps and/or the zooplankton that the polyp had trapped but not yet undigested. Also, the authors propose that to confirm the hypothesis it is necessary to carry out gut content and morphological analysis. I found the manuscript interesting and well written. I consider that this work is a good contribution to the field, however, I have few comments about some details in the text:

Response: Thank you very much

1. Line 65-66: Are you referring to figure 1a of this manuscript or to that of Malcolm et al., 1999? Please clarify.

Response: We have clarified it. It now reads: “dominated by antipatharians (Figure 1a) and a rich fish community (Malcolm et al. 1999).” (Line 65-66)

2. Line 94: Figures 2c,d do not exist, are you referring to figures 1c,d? change please.

Response: Yes, we were referring to Figure 1c,d. It has been corrected (Line 94).

Reviewer 2 Report

Please see attached document. 

Comments for author File: Comments.pdf

Author Response

Reviewer 2

In this work, the authors observed rabbitfish in the close vicinity of black corals. Because the polyps appeared intact, the authors ruled out coralivory and instead speculate that the fish were either consuming food trapped by the corals or are grazing microalgae that may have been coating them.

Response: We do not speculate the fish are grazing microalgae. We hypothesised that “S. javus on the Yongala are feeding on epibiotic algae or biofilms deposited on the antipatharians’ polyps and/or the zooplankton that the polyp had trapped but not yet indigested.” (Lines 86-88).

This is an interesting observation, and I do think it could have important implications. I would just like the authors to attempt to add more quantitative data into the mix, particularly to give an idea of just how prevalent this behavior was across the 10 dives. How many total rabbitfish-black coral interactions were observed?

Response: We have included the information. (Line 78)

Although it may be too late now, I recommend bringing an Olympus TG series camera on subsequent dives if budget permits; the macro (“microscope”) lens would actually allow for you to visualize whether the black coral surfaces that had been contacted by the rabbitfish had been completely denuded of microalgae/cyanobacteria.

Response: We used an Olympus TG5 to take the photo in Figure 1b, where it is visible that the polyps are not covered on turf algae or cyanobacteria.

I have some other small comments that I have provided below that I think could aid the article. I believe if the authors are better able to quantify their observations, this would make a nice “note” for Oceans. I would therefore deem this a major revision (though most comments will hopefully be able to be addressed easily).

Response: We have address your comments below

Major comments

1. Code and data availability: maybe I read this wrong, but will the data not be publicly available upon publication? It should be. I read this at present as “only available during peer review,” though hopefully I am simply mistaken.

Response: The data is currently private for peer review. It will be publicly available upon publication.

2. Since this is a short communication (“note”), I think the Introduction could really just be a single paragraph: coral-algal-fish interactions are important. Rabbitfish and black corals can be found in the same areas along the GBR. We saw them interacting and decided to investigate further.

Response: We are following Oceans ‘Communication’ type of article guidelines. We believe our introduction is of adequate length and provides what it expected by the journal: “place the study in a broad context and highlight why it is important’”

3. MDPI uses numerical references, but the in-text references are listed as Name, year. Please update accordingly.

Response: Oceans editorial team manages that before publication.

4. Figure 1 requires scale bars.

Response: Added

5. In the Results and Discussion, there is reference to Figure 2c, d, but I only see a single panel. Were there meant to be four panels?

Response: No, it should have been ‘Figure 1c,d’. It has been corrected now (Line 94).

6. For Figure 2, since you went through the trouble to obtain these data, I would take it one step further and do the statistical analysis to show if there were depth effects within each cover bin (or across all of them). It would be a two-way chi-squared test, and you could use annotation to show where there were significant differences on the figure itself.

Response: We tested it and found no significant effect of depth on the number of colonies in each algal cover percentage group (chi squared = 1.9, p = 0.6). See code for details.

7. Figure 2: Could you add a second y axis and plot rabbitfish densities across the algal bins to show if they were more prevalent in areas with more algae on the black corals (or at certain depths)? This might actually do better as a second panel, i.e., to show the rabbitfish density data. This gets to my major comment/suggestion: to give the reader an idea of just how prevalent this behavior is. Is the provided video the lone instance captured, or did you see it occur several times over the 10 dives?

Response: We did not collect data on the rabbitfish densities across the algal depth bands, but we do not believe that information will aid/support our hypothesis, or the aim of this communication. Our hypothesis would be further investigated by fish gut content and morphological analysis (Line 89-90). We have added the information on the prevalence of the observation across our dives (Line 78).

Minor comments

Minor comments-title page

1. Key words should be alphabetized. You may also consider “marine ecology.”

Response: That is not a requirement according to the guidelines provided on the website (https://www.mdpi.com/journal/oceans/instructions). We will do it if the editor requires it though.

2. Herbivorous “fish” in the abstract (not “fishes”).

Response: We are referring to the individuals of different species within the herbivorous group.

3. I would reword the first sentence to where it sounds like this is one of many important roles, as opposed to this being THE major role they play.

Response: Assuming the comment was referring to the Abstract, we have revised the sentence (Lines 12-14)

4. Coral-algal competition paradigm (no need for the “for space” since it is implied).

Response: We believe this might not be obvious to readers outside this field.

Minor comments-Introduction

1. ….maintain reef function (not “functioning”).

Response: Corrected (Line 27).

2. Coral and algae are not benthic “communities” but “taxa.” I know what you want to say, so maybe you could change the sentence to reflect that these are the two dominant benthic taxa in many shallow tropical and sub-tropical areas.

Response: Changed to ‘taxa’ (Line 28).

3. Black coral interactions with other reef organisms. “Symbiosis” is not the correct word here because you are talking about all interactions, not just the most intimate ones that symbiosis would entail.

Response: We have added ‘or interactions’ (Line 54).

4. Actually, there is a lot of work on fish-coral interactions. I think fish-BLACK CORAL interactions, on the other hand, have received less attention, so I think you need the word “black” in there or David Bellwood and Morgan Pratchett are going to feel hurt!

Response: We have added ‘in particular with black corals’ (Line 56).

Minor comments-results and discussion

1. Line 98: This is not evident from Figure 2. I suspect there may have been figures or panels of figures in older versions of the manuscript that were later removed. Please ensure that the figures and references are updated.

Response: No, it should have been Figure 1c,d. It has been corrected now (Line 94).

2. Line 107: I would try and use a more scientific word than “steal;” maybe “taking?”

Response: Changed to ‘taking’ (Lines 108, 110)

3. Line 112: no need for the comma

Response: Deleted (Line 112).

Minor comments-references

1. The references are formatted inconsistently; sometimes all words in an article are capitalized and sometimes not. I believe they should not be for MDPI.
2. Reference #5 has a typo at the end: “fee”
3. Reference #14 appears to be missing some information.

Response: References are carefully managed by Oceans editorial team. We will address it if the editor requires it though.

 

4. Lines 118-120 should be reworded as: “While no stomach content examination was conducted by Bos et al. (2017), the rabbitfish were only found to bite the bells of the jellyfish, not the tentacular area.”

Response: Changed (Line 120).

5. Line 125: were confirmed

Response: Changed (Line 127).

6. Lines 132-134: I would word this more cautiously because it implies that this is the first observation in which reef fish play a role other than grazing algae off reefs, but I feel certain there is a rich literature of other reef fish in which their effects on corals have been documented (e.g., coralivory studies). I think this might be the first to show that BLACK corals are influenced by rabbitfish. It would be cool to see in the future if these black corals benefit from the rabbitfish; maybe the rabbitfish are removing something that could smother the corals. Or maybe it’s the opposite: the rabbitfish are stealing their food!

Response: We are stating that is in relation to herbivorous fish not all reef fish. Indeed, it will be very interesting and important to find out.

Minor comments-figures

1. In Figure 2, it should be “% algal cover (cyanobacteria+other microalgae)” on the x axis.

Response: The figure legend states: “For short, only ‘Cyanobacteria’ was written on the x-axis label when referring to both cyanobacteria and turf algae” (Line 145-146). We have changed the axis legend on the figure to be ‘Cyanobacteria’ instead, since it is the predominant one.

Reviewer 3 Report

It is interesting observation in relation to the senescence of black corals. I have seen also similar algae turfs growing on Antipathella wollastoni in the Canaries. Authors may keep their eyes open to see parasitic zoanthids growing among the turfs too.

 

 

Author Response

Reviewer 3

It is an interesting observation in relation to the senescence of black corals. I have seen also similar algae turfs growing on Antipathella wollastoni in the Canaries. Authors may keep their eyes open to see parasitic zoanthids growing among the turfs too.

 Response: Thank you. Indeed, it seems to be a common occurrence but unfortunately not reported before. Reports of zoanthids overgrowing black corals have been reported here: doi.org/10.2984/66.1.4, and doi.org/10.1007/s12526-021-01184-x

 

 

Round 2

Reviewer 2 Report

Review of Gress et al. Oceans

 

Summary

            In this work, the authors observed rabbitfish in the close vicinity of black corals. Because the polyps appeared intact, the authors ruled out coralivory and instead speculate that the fish were either consuming food trapped by the corals or are grazing microalgae that may have been coating them. This is an interesting observation, and I do think it could have important implications. I would just like the authors to attempt to add more quantitative data into the mix, particularly to give an idea of just how prevalent this behavior was across the 10 dives. How many total rabbitfish-black coral interactions were observed? Although it may be too late now, I recommend bringing an Olympus TG series camera on subsequent dives if budget permits; the macro (“microscope”) lens would actually allow for you to visualize whether the black coral surfaces that had been contacted by the rabbitfish had been completely denuded of microalgae/cyanobacteria. I have some other small comments that I have provided below that I think could aid the article. I believe if the authors are better able to quantify their observations, this would make a nice “note” for Oceans. I would therefore deem this a major revision (though most comments will hopefully be able to be addressed easily). 

 

Major comments

1.    Code and data availability: maybe I read this wrong, but will the data not be publicly available upon publication? It should be. I read this at present as “only available during peer review,” though hopefully I am simply mistaken.

2.    Since this is a short communication (“note”), I think the Introduction could really just be a single paragraph: coral-algal-fish interactions are important. Rabbitfish and black corals can be found in the same areas along the GBR. We saw them interacting and decided to investigate further.

3.    MDPI uses numerical references, but the in-text references are listed as Name, year. Please update accordingly.

4.    Figure 1 requires scale bars.

5.    In the Results and Discussion, there is reference to Figure 2c, d, but I only see a single panel. Were there meant to be four panels?

6.    For Figure 2, since you went through the trouble to obtain these data, I would take it one step further and do the statistical analysis to show if there were depth effects within each cover bin (or across all of them). It would be a two-way chi-squared test, and you could use annotation to show where there were significant differences on the figure itself.

7.    Figure 2: Could you add a second y axis and plot rabbitfish densities across the algal bins to show if they were more prevalent in areas with more algae on the black corals (or at certain depths)? This might actually do better as a second panel, i.e., to show the rabbitfish density data. This gets to my major comment/suggestion: to give the reader an idea of just how prevalent this behavior is. Is the provided video the lone instance captured, or did you see it occur several times over the 10 dives?

 

Minor comments

Minor comments-title page

1.    Key words should be alphabetized. You may also consider “marine ecology.”

2.    Herbivorous “fish” in the abstract (not “fishes”).

3.    I would reword the first sentence to where it sounds like this is one of many important roles, as opposed to this being THE major role they play.

4.    Coral-algal competition paradigm (no need for the “for space” since it is implied).

 

Minor comments-Introduction

1.    ….maintain reef function (not “functioning”).

2.    Coral and algae are not benthic “communities” but “taxa.” I know what you want to say, so maybe you could change the sentence to reflect that these are the two dominant benthic taxa in many shallow tropical and sub-tropical areas.

3.    Black coral interactions with other reef organisms. “Symbiosis” is not the correct word here because you are talking about all interactions, not just the most intimate ones that symbiosis would entail.

4.    Actually, there is a lot of work on fish-coral interactions. I think fish-BLACK CORAL interactions, on the other hand, have received less attention, so I think you need the word “black” in there or David Bellwood and Morgan Pratchett are going to feel hurt!

 

Minor comments-results and discussion

1.    Line 98: This is not evident from Figure 2. I suspect there may have been figures or panels of figures in older versions of the manuscript that were later removed. Please ensure that the figures and references are updated.

2.    Line 107: I would try and use a more scientific word than “steal;” maybe “taking?”

3.    Line 112: no need for the comma

 

Minor comments-references

1.    The references are formatted inconsistently; sometimes all words in an article are capitalized and sometimes not. I believe they should not be for MDPI.

2.    Reference #5 has a typo at the end: “fee”

3.    Reference #14 appears to be missing some information.

4.    Lines 118-120 should be reworded as: “While no stomach content examination was conducted by Bos et al. (2017), the rabbitfish were only found to bite the bells of the jellyfish, not the tentacular area.”

5.    Line 125: were confirmed

6.    Lines 132-134: I would word this more cautiously because it implies that this is the first observation in which reef fish play a role other than grazing algae off reefs, but I feel certain there is a rich literature of other reef fish in which their effects on corals have been documented (e.g., coralivory studies). I think this might be the first to show that BLACK corals are influenced by rabbitfish. It would be cool to see in the future if these black corals benefit from the rabbitfish; maybe the rabbitfish are removing something that could smother the corals. Or maybe it’s the opposite: the rabbitfish are stealing their food!

 

Minor comments-figures

1.    In Figure 2, it should be “% algal cover (cyanobacteria+other microalgae)” on the x axis.

Author Response

We have already revised the manuscript based on previous comments. Please see below.

 

Reviewer 2

In this work, the authors observed rabbitfish in the close vicinity of black corals. Because the polyps appeared intact, the authors ruled out coralivory and instead speculate that the fish were either consuming food trapped by the corals or are grazing microalgae that may have been coating them.

Response: We do not speculate the fish are grazing microalgae. We hypothesised that “S. javus on the Yongala are feeding on epibiotic algae or biofilms deposited on the antipatharians’ polyps and/or the zooplankton that the polyp had trapped but not yet indigested.” (Lines 86-88).

This is an interesting observation, and I do think it could have important implications. I would just like the authors to attempt to add more quantitative data into the mix, particularly to give an idea of just how prevalent this behavior was across the 10 dives. How many total rabbitfish-black coral interactions were observed?

Response: We have included the information. (Line 78)

Although it may be too late now, I recommend bringing an Olympus TG series camera on subsequent dives if budget permits; the macro (“microscope”) lens would actually allow for you to visualize whether the black coral surfaces that had been contacted by the rabbitfish had been completely denuded of microalgae/cyanobacteria.

Response: We used an Olympus TG5 to take the photo in Figure 1b, where it is visible that the polyps are not covered on turf algae or cyanobacteria.

I have some other small comments that I have provided below that I think could aid the article. I believe if the authors are better able to quantify their observations, this would make a nice “note” for Oceans. I would therefore deem this a major revision (though most comments will hopefully be able to be addressed easily).

Response: We have address your comments below

Major comments

1. Code and data availability: maybe I read this wrong, but will the data not be publicly available upon publication? It should be. I read this at present as “only available during peer review,” though hopefully I am simply mistaken.

Response: The data is currently private for peer review. It will be publicly available upon publication.

2. Since this is a short communication (“note”), I think the Introduction could really just be a single paragraph: coral-algal-fish interactions are important. Rabbitfish and black corals can be found in the same areas along the GBR. We saw them interacting and decided to investigate further.

Response: We are following Oceans ‘Communication’ type of article guidelines. We believe our introduction is of adequate length and provides what it expected by the journal: “place the study in a broad context and highlight why it is important’”

3. MDPI uses numerical references, but the in-text references are listed as Name, year. Please update accordingly.

Response: Oceans editorial team manages that before publication.

4. Figure 1 requires scale bars.

Response: Added

5. In the Results and Discussion, there is reference to Figure 2c, d, but I only see a single panel. Were there meant to be four panels?

Response: No, it should have been ‘Figure 1c,d’. It has been corrected now (Line 94).

6. For Figure 2, since you went through the trouble to obtain these data, I would take it one step further and do the statistical analysis to show if there were depth effects within each cover bin (or across all of them). It would be a two-way chi-squared test, and you could use annotation to show where there were significant differences on the figure itself.

Response: We tested it and found no significant effect of depth on the number of colonies in each algal cover percentage group (chi squared = 1.9, p = 0.6). See code for details.

7. Figure 2: Could you add a second y axis and plot rabbitfish densities across the algal bins to show if they were more prevalent in areas with more algae on the black corals (or at certain depths)? This might actually do better as a second panel, i.e., to show the rabbitfish density data. This gets to my major comment/suggestion: to give the reader an idea of just how prevalent this behavior is. Is the provided video the lone instance captured, or did you see it occur several times over the 10 dives?

Response: We did not collect data on the rabbitfish densities across the algal depth bands, but we do not believe that information will aid/support our hypothesis, or the aim of this communication. Our hypothesis would be further investigated by fish gut content and morphological analysis (Line 89-90). We have added the information on the prevalence of the observation across our dives (Line 78).

Minor comments

Minor comments-title page

1. Key words should be alphabetized. You may also consider “marine ecology.”

Response: That is not a requirement according to the guidelines provided on the website (https://www.mdpi.com/journal/oceans/instructions). We will do it if the editor requires it though.

2. Herbivorous “fish” in the abstract (not “fishes”).

Response: We are referring to the individuals of different species within the herbivorous group.

3. I would reword the first sentence to where it sounds like this is one of many important roles, as opposed to this being THE major role they play.

Response: Assuming the comment was referring to the Abstract, we have revised the sentence (Lines 12-14)

4. Coral-algal competition paradigm (no need for the “for space” since it is implied).

Response: We believe this might not be obvious to readers outside this field.

Minor comments-Introduction

1. ….maintain reef function (not “functioning”).

Response: Corrected (Line 27).

2. Coral and algae are not benthic “communities” but “taxa.” I know what you want to say, so maybe you could change the sentence to reflect that these are the two dominant benthic taxa in many shallow tropical and sub-tropical areas.

Response: Changed to ‘taxa’ (Line 28).

3. Black coral interactions with other reef organisms. “Symbiosis” is not the correct word here because you are talking about all interactions, not just the most intimate ones that symbiosis would entail.

Response: We have added ‘or interactions’ (Line 54).

4. Actually, there is a lot of work on fish-coral interactions. I think fish-BLACK CORAL interactions, on the other hand, have received less attention, so I think you need the word “black” in there or David Bellwood and Morgan Pratchett are going to feel hurt!

Response: We have added ‘in particular with black corals’ (Line 56).

Minor comments-results and discussion

1. Line 98: This is not evident from Figure 2. I suspect there may have been figures or panels of figures in older versions of the manuscript that were later removed. Please ensure that the figures and references are updated.

Response: No, it should have been Figure 1c,d. It has been corrected now (Line 94).

2. Line 107: I would try and use a more scientific word than “steal;” maybe “taking?”

Response: Changed to ‘taking’ (Lines 108, 110)

3. Line 112: no need for the comma

Response: Deleted (Line 112).

Minor comments-references

1. The references are formatted inconsistently; sometimes all words in an article are capitalized and sometimes not. I believe they should not be for MDPI.
2. Reference #5 has a typo at the end: “fee”
3. Reference #14 appears to be missing some information.

Response: References are carefully managed by Oceans editorial team. We will address it if the editor requires it though.

 

4. Lines 118-120 should be reworded as: “While no stomach content examination was conducted by Bos et al. (2017), the rabbitfish were only found to bite the bells of the jellyfish, not the tentacular area.”

Response: Changed (Line 120).

5. Line 125: were confirmed

Response: Changed (Line 127).

6. Lines 132-134: I would word this more cautiously because it implies that this is the first observation in which reef fish play a role other than grazing algae off reefs, but I feel certain there is a rich literature of other reef fish in which their effects on corals have been documented (e.g., coralivory studies). I think this might be the first to show that BLACK corals are influenced by rabbitfish. It would be cool to see in the future if these black corals benefit from the rabbitfish; maybe the rabbitfish are removing something that could smother the corals. Or maybe it’s the opposite: the rabbitfish are stealing their food!

Response: We are stating that is in relation to herbivorous fish not all reef fish. Indeed, it will be very interesting and important to find out.

Minor comments-figures

1. In Figure 2, it should be “% algal cover (cyanobacteria+other microalgae)” on the x axis.

Response: The figure legend states: “For short, only ‘Cyanobacteria’ was written on the x-axis label when referring to both cyanobacteria and turf algae” (Line 145-146). We have changed the axis legend on the figure to be ‘Cyanobacteria’ instead, since it is the predominant one.