Small Jellyfish as a Supplementary Autumnal Food Source for Juvenile Chaetognaths in Sanya Bay, China
Round 1
Reviewer 1 Report
Dear authors,
I carefully read your manuscript "Small jellyfish as a supplementary autumnal food source for juvenile chaetognaths in Sanya Bay, China".
You tackled a very interessting topic, however, I have some general concerns about the manuscript in the current form. There is some need to revise it before it can be considered for publication.
The introduction is a very nice summary of the current state of the art in this field, however, I miss a clear hypotheses or research question leading to the observational study you presented here. It would be nice to clearly state the importance of the knowledge gain, the reader get from your study.
Ending the introduction with a strong hypothesis builds up the strengths and importance of the data you present afterwards.
Methods are clearly described. Still, I have some comments on the methods specifically on the sampling itself. You report that you sampled in a similar way at three different sites in the bay, however, the sampling depth was always different! Please clarify this and how this might influence your results. I assume you sampled during day and a lot of zooplankton do some vertical migration over 24h. Please clarify how this might have influenced your data and the outcome of your study. Another issue with sampling is that all samples at one site in each season were taken at the same time point. Given the fact that all organisms in this study have longer generation times, it would be beneficial if there would be more information about the zooplankton composition 1-2 weeks before too. As the response of the chaetognaths population might strongly depend on the zooplankton composition prior to the sampling day.
You state that the environmental parameter stayed constant over the two seasons. Do you have some Chla or general phytoplankton data and nutrient data you could provide here as well? As it is a very important aspect of the nutrition of the zooplankton. In line 192-200 there are some values given where I was a bit confused. Please revise this part.
The discussion nicely incorporates currents studies, however, lack in novelty. As your title expresses a new food source for chaetognaths, this point is only briefly discussed in the very last part. The data are for sure of interest in the field, however, there is a lack of discussion how you interpret these findings and how important they might be for the food web. Presenting two distinct time points might give a snapshot of the population dynamic here, but it is a bit too far to speak about population dynamics of this species in general.
In my opinion, before one could go into a very detailed review of the text, these general comments should be addressed. There are some typos and species names are sometimes not written in italic, however, these are minor issues.
Author Response
- The introduction is a very nice summary of the current state of the art in this field, however, I miss a clear hypotheses or research question leading to the observational study you presented here. It would be nice to clearly state the importance of the knowledge gain, the reader get from your study. Ending the introduction with a strong hypothesis builds up the strengths and importance of the data you present afterwards.
Response: The last paragraph of “Introduction” part has been modified as suggested and the hypothesis was made clear (Lines 72-83)
- Methods are clearly described. Still, I have some comments on the methods specifically on the sampling itself. You report that you sampled in a similar way at three different sites in the bay, however, the sampling depth was always different! Please clarify this and how this might influence your results. I assume you sampled during day and a lot of zooplankton do some vertical migration over 24h. Please clarify how this might have influenced your data and the outcome of your study. Another issue with sampling is that all samples at one site in each season were taken at the same time point. Given the fact that all organisms in this study have longer generation times, it would be beneficial if there would be more information about the zooplankton composition 1-2 weeks before too. As the response of the chaetognaths population might strongly depend on the zooplankton composition prior to the sampling day.
Response: The sampling depth is 19-30m in three stations. Though the sampling depth are different, as we collect the sample by vertical trawl, the ambient zooplankton structure has not significant difference among stations according to our results. Also, the feeding results of juvenile chaetognaths were also similar from phylum levels among stations. As for the zooplankton diel migration, this is a very interesting question. As the samples were collected just in one time point, diel samplings were needed in further experiment design. For the final suggestion, it is very good suggestion. If we have information about the zooplankton composition 1-2 weeks before would be better to explain their feeding strategy. It also can answer the real time diet composition from our results and partly explain the feeding strategy of the juvenile chaetognath abundant season.
- You state that the environmental parameter stayed constant over the two seasons. Do you have some Chla or general phytoplankton data and nutrient data you could provide here as well? As it is a very important aspect of the nutrition of the zooplankton. In line 192-200 there are some values given where I was a bit confused. Please revise this part.
Response: We have added Chla data and made revision as suggested (Lines 167-168; 196).
- The discussion nicely incorporates currents studies, however, lack in novelty. As your title expresses a new food source for chaetognaths, this point is only briefly discussed in the very last part. The data are for sure of interest in the field, however, there is a lack of discussion how you interpret these findings and how important they might be for the food web. Presenting two distinct time points might give a snapshot of the population dynamic here, but it is a bit too far to speak about population dynamics of this species in general.
Response: We totally agree this suggestion and we revised the discussion and especially the last paragraph to focus on the meaning of the findings. We added more details about the trophic ecology role of jellyfish (Lines 316-326).
- There are some typos and species names are sometimes not written in italic.
Response: We have checked and revised the species names of the whole manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments on the manuscript (jmse-978647)
General:
This manuscript revealed food items of juvenile chaetognaths in the tropical shallow embayment based on the molecular analysis of their gut contents. As a result, the authors concluded that the small jellyfishes may important food sources for the juvenile chaetognaths in a limited season (autumn). The obtained results and their conclusion are interest. Since the jellyfishes are difficult to identify from the gut content analysis by ordinally classical microscopic analysis. Thus, the applied method by the authors may overcome this problem. From this point of view, I want to recommend accepting the manuscript after careful consideration of the following detailed comments listed below.
First, how about the size of three organisms? Since as the food items of chaetognaths, the authors listed as copepods in summer and jellyfishes in autumn. The body size interaction of them (chaetognaths, copepods, and jellyfishes) is an important factor to consider how they feed the prey. While the authors discussed that the chaetognaths may feed on jellyfish detritus (L299), why they could not feed directly on living jellyfishes? Since the authors may have the formalin preserved samples, the body sizes of each component may easily be photographed and presentation of the picture for comparing their body size may help the readers to consider the adequation of the authors’ argument.
The second is the presentations in the figure. The authors applied two figures: Fig. 1 is for the map, and Fig. 2 is for the gut content. For Fig. 1, it is meaningless to show the study area. They did not compare results between stations and their map is too rough and it should be removed. Instead of the map, I want to recommend the authors to show the figure to represent the results of ambient zooplankton. In the present form, the authors presented the data on the ambient zooplankton as Appendix A and cited it frequently (see L172, 187, 191, 193). It should be presented in Figure (Fig. 1). Thus, I want to recommend the authors to present three figures: the new Fig. 1 for ambient zooplankton which shown in Appendix A in the present form, Fig. 2 (molecular analysis on gut contents) is OK, and the new Fig. 3 on the picture on juvenile chaetognaths, copepods, and small jellyfishes, to show the relative size interaction of them. From these three-figure set, the readers may easily understand their conclusions.
Detailed:
L137: Show italic for F. enflata.
L163: Show italic for p>0.05.
L165, 167: Same for the above comment.
L174: Superscript for -3, and italic for p.
L185, 188: Species names should be shown in italics.
L193: the values citing in the parentheses are the opposite: thus, 11.23 for autumn, and 2.90 for summer. Please check and correct.
L208, 209: Show italic for p>0.05.
L211: Species names should be shown in italic.
L240: It may better to avoid using the term “jellyfish”. Use exact taxonomic name.
L280, 281: Species names should be shown by italics, and use italic for p>0.05.
L291: Kruse et al. (2010). Add “et al.”.
L292: Giesecke and Gonzalez (2012). Add “and Gonzalez”.
L296-299: Since the relative size interactions between jellyfish and chaetognaths are not mentioned in the manuscript, the authors' discussion (the chaetognaths feed on the jellyfish detritus) sounds abrupt. To avoid such a feeling, showing their relative sizes by adding Fig. 3 on the three components of this study (chaetognaths, copepods, and jellyfishes) may valuable.
Table 1: For salinity, show 35.00 at St. W4 (same digit for the other numbers).
Fig. 2: “small jellyfish” is not an adequate taxonomic name here. Please use as “Cnidaria” and “Ctenophora” which are comparable for the other taxonomic representation in the panel.
Appendix A: Break of the line may be needed between July 2014 and October 2014. For “Range” of October 2014, the “±” should be replaced by “-“. For taxonomic classification, why the only jellyfish is not followed with the presentation styles of the other taxa? It should be separated as Cnidaria and Ctenophora.
Appendix B: There are duplicate lines are available for the same species (see lines 3-5 [Temora turbinata] and lies 6-8 [Canthocalanus pauper] in W3-Sagen-Jul-j_diet). Why the authors show them separately? Is it OK to show them by sum? Please note that the similar presentations are available for the other Clone-ID also.
Appendix C: Break of the line is needed between Summer and Autumn. It is anomalous that the presence of the taxa that only occurred at ambient or occurred for the gut content. To avoid such anomalous presentation, showing taxonomic levels more summarized style such as family may better to consider.
Author Response
- First, how about the size of three organisms? Since as the food items of chaetognaths, the authors listed as copepods in summer and jellyfishes in autumn. The body size interaction of them (chaetognaths, copepods, and jellyfishes) is an important factor to consider how they feed the prey. While the authors discussed that the chaetognaths may feed on jellyfish detritus (L299), why they could not feed directly on living jellyfishes? Since the authors may have the formalin preserved samples, the body sizes of each component may easily be photographed and presentation of the picture for comparing their body size may help the readers to consider the adequation of the authors’ argument.
Response: We have added Figure 4 to show the relative size interaction of juvenile chaetognaths, small jellyfish, and copepod nauplii. Also, from the size relationship we think chaetognaths could feed directly on living jellyfishes, we have revised related sentences in the abstract and the discussion (Lines 28-30; 298-300).
- The second is the presentations in the figure. The authors applied two figures: Fig. 1 is for the map, and Fig. 2 is for the gut content. For Fig. 1, it is meaningless to show the study area. They did not compare results between stations and their map is too rough and it should be removed. Instead of the map, I want to recommend the authors to show the figure to represent the results of ambient zooplankton. In the present form, the authors presented the data on the ambient zooplankton as Appendix A and cited it frequently (see L172, 187, 191, 193). It should be presented in Figure (Fig. 1). Thus, I want to recommend the authors to present three figures: the new Fig. 1 for ambient zooplankton which shown in Appendix A in the present form, Fig. 2 (molecular analysis on gut contents) is OK, and the new Fig. 3 on the picture on juvenile chaetognaths, copepods, and small jellyfishes, to show the relative size interaction of them. From these three-figure set, the readers may easily understand their conclusions.
Response: For Fig. 1, we prefer to retain the use of Figure 1 for reasons that it could provide basic geographic information for readers about where the Sanya Bay located in the south China sea and the sampling station located in the Sanya bay. Besides, these three stations are not so closely to nearshore which could reduce the disturbance of human activities. For the represent the results of ambient zooplankton, we have added Figure 2 for the zooplankton structure which shown in Appendix A. For the last suggestion, we have added Figure 4 to show the relative size interaction of juvenile chaetognaths, small jellyfish, and copepod nauplii.
- Detailed:
L137: Show italic for F. enflata.
Response: We have shown italic for F. enflata. Lines: 132,137
L163: Show italic for p>0.05.
Response: We have shown italic for p>0.05. Line: 163
L165, 167: Same for the above comment.
Response: We have shown italic for p. Lines: 165, 167
L174: Superscript for -3, and italic for p.
Response: We have superscript for -3, and italic for p. Line: 175
L185, 188: Species names should be shown in italics.
Response: We have shown italic for F. enflata. Lines: 188, 191
L193: the values citing in the parentheses are the opposite: thus, 11.23 for autumn, and 2.90 for summer. Please check and correct.
Response: We have corrected the values. Line: 196
L208, 209: Show italic for p>0.05.
Response: We have shown italic for p>0.05. Lines: 211-212
L211: Species names should be shown in italic.
Response: We have shown italic for F. enflata. Line: 214
L240: It may better to avoid using the term “jellyfish”. Use exact taxonomic name.
Response: We have revised this term and use “Cnidaria” and “Ctenophora”. Lines 242,243
L280, 281: Species names should be shown by italics, and use italic for p>0.05.
Response: We have reorganized this paragraph and shown italic for species names.
L291: Kruse et al. (2010). Add “et al.”.
Response: We have added “et al” after “Kruse”. Line 283
L292: Giesecke and Gonzalez (2012). Add “and Gonzalez”.
Response: We have added “and Gonzalez” after “Giesecke”. Line 285
L296-299: Since the relative size interactions between jellyfish and chaetognaths are not mentioned in the manuscript, the authors' discussion (the chaetognaths feed on the jellyfish detritus) sounds abrupt. To avoid such a feeling, showing their relative sizes by adding Fig. 3 on the three components of this study (chaetognaths, copepods, and jellyfishes) may valuable.
Response: We have added Figure 4 to show the relative size interaction of juvenile chaetognaths, small jellyfish, and copepod nauplii.
Table 1: For salinity, show 35.00 at St. W4 (same digit for the other numbers).
Response: We have shown 35.00 at St. W4. Line169
Fig. 2: “small jellyfish” is not an adequate taxonomic name here. Please use as “Cnidaria” and “Ctenophora” which are comparable for the other taxonomic representation in the panel.
Response: We have revised this term and use “Cnidaria” and “Ctenophora” instead of “small jellyfish”, see in Figure 3.
Appendix A: Break of the line may be needed between July 2014 and October 2014. For “Range” of October 2014, the “±” should be replaced by “-“. For taxonomic classification, why the only jellyfish is not followed with the presentation styles of the other taxa? It should be separated as Cnidaria and Ctenophora.
Response: We have added the break line between July 2014 and October 2014. “Range” of October 2014, the “±” has all been replaced by “-”. We have separated “jellyfish” as “Cnidaria” and “Ctenophora”.
Appendix B: There are duplicate lines are available for the same species (see lines 3-5 [Temora turbinata] and lies 6-8 [Canthocalanus pauper] in W3-Sagen-Jul-j_diet). Why the authors show them separately? Is it OK to show them by sum? Please note that the similar presentations are available for the other Clone-ID also.
Response: We show them separately because the similarities are different. We separate them in 3% and think it is not Ok to show them by sum. Because the higher percentage of similarity means they are more likely to this species. The similarity of 90-92% means the sequence detected may only can identified to the phylum of this species.
Appendix C: Break of the line is needed between Summer and Autumn. It is anomalous that the presence of the taxa that only occurred at ambient or occurred for the gut content. To avoid such anomalous presentation, showing taxonomic levels more summarized style such as family may better to consider.
Response: We have added the break line between July 2014 and October 2014. We have revised and shown taxonomic levels more summarized style “family” in Appendix C.
Author Response File: 
Author Response.docx
Round 2
Reviewer 1 Report
Dear Authors,
I read through the revised version of the manuscript.
You nicely addressed the comments. However, I still struggle with the fact, that the the increased growth of chaetognaths is only due to the additional nutrition of small jellies. I do not think this is untrue, however, only a zooplankton sample from an earlier time point of other zooplankton prior to the sampling day would eclude the possibility of other zooplnakton peak, which could also lead to the increase of chaetogneths. Nevertheless, the jellies wills till contribute for sure!
Otherwise, nice study!
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
