Food Sources for Benthic Grazers in Trophic Networks of Macrophyte Habitats in a Transitional Baltic Ecosystem

Round 1

Reviewer 1 Report

Review comments on water manuscript

 

This study examined trophic structure of littoral food web in a lagoon system using stable isotope signature of major basal food resources as well as consumers. Although I acknowledge the value of study to some extent, there were several places where I am confused about the contents. I believe that there are major problems in analytical approaches and some of the result interpretations.

 

 

L.84: The aim or objective of this study is unclear and partially inconsistent with what seemed to have been carried out. Specifically, the TL of consumers were probably estimated (L. 208-) and it reads these TL were for animals other than grazers because some of grazer values were used as baseline to estimate others. Then, the question is why was it necessary to estimate TL of others not the base line animals (L.206-) when the study aim was to focus on base-line organisms (L.84, and L.89, specially), i.e. gastropoda and amphipoda?

 

L.93: Why were those two specific sites were selected? How were they representative of other similar sites in the lagoon? Strong statement to support the reason is needed partially because there were not spatial or temporal replicates.

 

L.125: Was the pore size for GF/F 0.22µm not 0.7µm as described in the line 140 later?

 

L.209: Bithynia tentulata, is probably misspelled (this should be Bithynia tentaculate probably as were in other places in the text).

 

L.210: I understand that those grazers were used as base-line delta15N for TL estimate of others. However, I am very confused about how TL_baseline was calculated. There was no mentioning to how they were measured (I can very weakly assume based on the table 1, they were assigned to TP 2.0… as they are considered as primary consumer grazers, but this needs to be clearly stated). Also, those two species in Mollusca was used as baseline without much justifications. While the authors called amphipoda also as grazers, as in L.84,85 (I guess these amphipods included those crustaceans shown in Table1?). If so, why then were those not used as baseline but only selected two species were selected as grazers. I do not understand well the logic behind this approach.

 

Figure 2: Provide explanations about different types of symbols used in the figure

 

L.250: Macrophyte grow on ..? Something might be wrong grammatically. I did not understand that was meant by this sentence.

 

Table 2: Table caption must be provided properly.

 

L.348: Connected processes; the meaning is unclear, and needs to be rephrased

 

L.355: Because there are no explanations of what the expectations are when productivity explain the gradient, the sentence meaning is unclear. Possibly revise by rephrasing it or adding more explanations.

 

L.388: What kind of environmental factors possibly explained the gradient? Some explanations need to be provided in relation to general or site-specific knowledge of isotope representation of the environment.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Review of

Food Sources for benthic grazers in trophic networks of macrophyte habitats in a transitional Baltic ecosystem.

 

This well written paper explores the ecological differences between two sites in the Baltic with a focus on the macrophyte habitats. This is an excellent paper although limited by the data involved being both site limited and also temporally limited. The methods are sound although my main criticism is the use of simple statistics to view the differences within a complex dependent environment.

My comments are minor:

1. Figure 1. Can the gradients being described in line 71 be shown on the map.
2. Line 93. How exactly were the sites selected? Does this influence the results.
3. Line 185. I appreciate the difficulty in collecting data at this level of intensity and the limitations in comparing two sites. However, there are some solid data to play with and it seems a pity that methods that do not violate assumptions of independence and normality are used. Methods like Random Forests or Bayesian Networks can handle the complex interactions more securely. Comparing various distributions on a simple basis limits the conclusions about the factors involved.
4. Table 2 citation was scrambled.
5. Can the results be translated to a graphical model of the trophic system? Perhaps in a classic network manner?
6. Line 348 remove ‘of’
7. Line 353. Any comments on using other isotope combinations to explore this relationship.
8. Line 365. Can the authors comment on the variability in the system especially for the sample period. Was this a particularly unusual year or season? Is there a reference that explores that variability?
9. Line 410. Is there a lag from the summer and northern site for the onset of the seasons?
10. Line 434 any comments on the likely influence of the larger fish that migrate through both sites and may influence the habitat character?
11. Line 439 add ‘having’
12. Appendix B is in the draft but is not used.
13. There is merit in comparing the stomach content from other studies. See Neuenfeldt, S., Bartolino, V., Orio, A., Andersen, K.H., Andersen, N.G., Niiranen, S., Bergström, U., Ustups, D., Kulatska, N. and Casini, M., 2020. Feeding and growth of Atlantic cod (Gadus morhua L.) in the eastern Baltic Sea under environmental change. ICES Journal of Marine Science, 77(2), pp.624-632 noting that this does not focus on your fish species.

Author Response

Please see the attachment.

Author Response File: Author Response.docx