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Thank you for submitting the revised version of your manuscript to PeerJ.
In the revised version the authors took into consideration all comments and remarks. I recommend accepting your manuscript for publication in PeerJ.
[# PeerJ Staff Note - this decision was reviewed and approved by Dezene Huber, a PeerJ Section Editor covering this Section #]
Dear Dr. Campbell,
Your submission has been reviewed. The reviewers provided detailed comments, and I ask that you consider these carefully and correct the errors when revising the manuscript.
Although the reviewers referred to the corrections as "minor revisions," I found their criticism to be serious, so you should pay special attention to their comments.
I look forward to receiving your revised revision.
Language is clear, intelligible and professional. But there are some typing and grammatical errors which should be corrected.
Introduction is sufficient and gives clear background to understanding of the problem.
Structure of the article is conformed to the acceptable format. Figures have sufficient resolution. However, some minor corrections are necessary in Figs and Tables. Citing literature should be checked.
The research question and knowledge gap is clearly defined. In general Methods described with sufficient detail to replicate. Geographic coordinates of sampling sites provided in Supplemental materials are very useful for further monitoring of the lagoon ecosystem.
The findings provide new comprehensive knowledge about seagrass distribution, coverage and biomass within one of the impacted lagoons of the Panama. Also data on the elemental and stable isotopic composition of the seagrass and their spatial variability were obtained. Such data are required to understand the current state of the lagoon ecosystem, health of the seagrass community and to provide baseline data for monitoring programs.
The main goal of the revised study was to provide expaned data on the distribution and coverage of Thalassia testudinum as well as the elemental and stable isotopic composition in its leaves in Bahia Almirante, a lagoon exposed to anthropogenic press, to estimate the current health state of the lagoon ecosystem and provide a baseline dataset for the monitoring programs. To achieve this aim, a comprehensive bay-wide sampling in single survey was done, at each site the coverage, biomass and seagrass bio-indicators such as leaf morphology, tissue carbon, nitrogen and phosphorus content and stable isotopic signatures were obtained. The obtained results are clear and support conclusions. The manuscript is clearly written in professional, unambiguous language. If there is a weakness, then this is some negligence in the design of figures, tables and literature (as I have noted below). The article can be published after revision.
Basic reporting
Language is clear, intelligible and professional. But there are some typing and grammatical errors which should be corrected.
Introduction is sufficient and gives clear background to understanding of the problem.
Structure of the article is conformed to the acceptable format. Figures have sufficient resolution. However, some minor corrections are necessary in Figs and Tables. Citing literature should be checked.
Experimental design
The research question and knowledge gap is clearly defined. In general Methods described with sufficient detail to replicate. Geographic coordinates of sampling sites provided in Supplemental materials are very useful for further monitoring of the lagoon ecosystem.
Validity of the Findings
The findings provide new comprehensive knowledge about seagrass distribution, coverage and biomass within one of the impacted lagoons of the Panama. Also data on elemental and stable isotopic composition of the seagrass and their spatial variability were obtained. Such data are required to understand the current state of the lagoon ecosystem, the health of the seagrass community and to provide baseline data for monitoring programs.
Specific comments
All references cited in the text should be provided in the References list and vice versa. Those are CARICOMP (there are not it in the references list, I believe you mind UNESCO (1998)), Fourqurean & Rutten, 2003 (absent in the references list), Ralph et al. 2007 (does not cited in the text). At lines 180 and 379 Atkinson, Smith (1982) should be 1983. I am not sure but in my feeling the references cited only in Table S5 are not needed in the main References list. Please consult the editor on this matter. Also for references marked with a, b and ets. it is better to give letters as the Reference appears in the text. Sometimes "a" follows "b". This rule is right for the Figs numbers (for example Fig7 a,b,c,d,e at lines 263-279). What are Reference you mean at lines 177 (Fourqurean et al., 1992) and 363 (Carruthers et al., 2005), a or b? At line 430 O’Leary et al. 2017 not O’leary.
Abstract
The statement “The high nutrient availability and depth-restricted distribution of seagrasses suggest that many of these meadows may be approaching or have already surpassed a ‘tipping point’, in which seagrasses retreat to shallower depth” is not fully supported by the results. I suggest that you provide data on depth limit of Thalassia testudinum in intact areas in the other regions or early data on it vertical distribution in the studied area, to provide more justification for this statement.
Figures
The signature of Y axis at Figs. 2b, 4b, 7a and 7b should be changed as g dry mass m-2 or g dry weight m-2. Similarly it should be done in Table S4 (last column) and Table 1 (last column).
Fig. 1. Because you claiming that “Bahja Almirante receives moderate to high freshwater input and nutrient loading from the inflowing rivers” it would be helpful to map the rivers or river mouth in the Fig. This can help audience in understanding of the impact of land runoff on lagoon's ecosystem.
Minor changes over the text
Lines 160-161 check the punctuation.
Lines 164 and 168. The abbreviation DI is not needed after distillated water.
Line 300 The benthic community at all sites was dominated
Lines 327 and 328. While two sampling sites are in reserve areas (Site 4 is in Matumbal Bay Special Use Zone and Site 8 is in Isla Bastimentos National Marine Park)
Line 389. site, we found a significant…
Line 421 - 422. "these meadows may be characterized as relatively eutrophic". Eutrophy is a characteristic of a water area, not of a community.
Clear, unambiguous, professional English language used throughout. Intro & background to show context. Literature is redundant. Structure conforms to PeerJ standards, discipline norm. Some figures are inappropriately described and labeled. Raw data supplied.
Original primary research within Scope of the journal. Research question well defined, relevant & meaningful. It is stated how the research fills an identified knowledge gap. Rigorous investigation performed to a technical & ethical standard. Methods described with sufficient detail & information to replicate.
All underlying data have been provided; they are robust and controlled. Conclusions are not well stated, are not well linked to original research question & are not limited to supporting results.
In the manuscript “Seagrass structural and elemental indicators reveal high nutrient availability within a tropical lagoon in Panama” the authors presented a comprehensive dataset on seagrass coverage and composition across 24 sites in Bahía Almirante Bay, using a single survey. They focused on spatial variation in leaf morphology (length and width), elemental content (% nitrogen and phosphorus) and stable isotopic signatures (δ13C and δ15N) in the dominant turtlegrass Thalassia testudinum. The sensitivity of seagrasses in Bahía Almirante to light and depth was revealed. The authors documented the eutrophic status of this bay. Additionally, they conducted a literature review to compare N and P content in the leaf to values reported for T. testudinum in other regions across the Caribbean Sea.
It is good work; however, I see some inconsistencies here.
1. It was “single time point”, the authors did not include monitoring of the benthic community of the bay in the goals of the work, but they devoted two paragraphs to it in the Introduction, made assumptions in the Discussion and Conclusion. If they wanted to focus on monitoring of the benthic community in the bay, then it would be correct to make a comparative analysis of their results with data on seagrass temporal variability of Caribbean Coastal Marine Productivity Program (1998) for two sites of Bahía Almirante, as well as with the study described T. testudinum nutrient content for three sites of the Bocas archipelago (Carruthers et al. 2005b). At the same time, it is necessary to make appropriate additions to the goals of the work and in M&M. If monitoring will be included in the goals of the work, then Fig. 6 should indicate the average values obtained by the authors only for points close to the sites that were studied earlier (Carruthers et al. 2005). Without this analysis, the monitoring text must be removed from the manuscript or minimized upon before acceptance.
2. There is a weakness in the statistical analysis. Before a statistical comparison, the proportional data must be transformed (square root or arcsin), as they are percentages. I think that untransformed data set may be the reason of unsatisfactory results of the cluster analysis of the benthic community composition between sites that used % cover per group. If the benthos is primarily composed of bare sediment or covered practically only by dominant T. testudinum, corresponding % data gives too heavy weight in calculations, crushing data on other components of the community. If the authors still will not get an interesting result, then the cluster analysis could be excluded from the results of the work. The authors' comparative analysis of the composition of communities living near the open ocean, the city and other areas is quite good and relevant. And it will not be necessary to keep silent about the places that did not fall into the cluster, or for some reason fell into one large (medium) cluster.
3. I think that the calculation of the mean value, and especially SE and CV, for biomass is incorrect since the distribution is far from the normal distribution. It is advisable to enter the data in the text what is the fundamental difference between places with a biomass of 20-40 and 120-140 g per m2. There may be different stages of succession, or/and different growth rates. May be they are young and old individuals?
4. References are too mach.
Some notes on the text, tables, and figures:
Line 61. Seagrasses are sensitive to light not only in Bahía Almirante. The authors did not study nutrient availability in the bay water or bottom sediment.
The sentences located on lines 64-66 and 127-128 should be removed.
Lines 62-64. I do not understand why “The high nutrient availability and depth-restricted distribution of seagrasses suggest that many of these meadows may be approaching or have already surpassed a ‘tipping point’, in which seagrasses retreat to shallower depth”.
The sentences located on lines 112-113, 193-195 and 280-282 should be supplemented with references.
Lines 172 and 308-309. What means “long-lived”?
Lines 172-175 and 182-195. The literature data and the justification for the need to study N, P, δ15N and δ13C contents should be included in the Introduction.
Lines 189 and 199. It is necessary to transcribe the abbreviations DIC and IRMS.
Lines 280-282. Need to move it to the Discussion.
Lines 388-389. Mathematical statistics allows you to remove extreme bouncing values from the dataset, however, if there is a lot of data.
Table 2. It is necessary to explain the reason for the appearance of a large SE value and why the median is much higher than the mean value.
Fig. 1 or Fig. 3. It is desirable to draw isobath.
Figs 2 and 6. It is necessary to draw (a), (b), (c), etc.
Fig. 4. It is necessary to enter in M&M an explanation of why the transformed data is shown on the Y-axis, and not the absolute values.
Fig. 4b. It is necessary to draw a regression line and specify the correlation coefficient.
Fig. 6. It is necessary to include in the table title, which is shown by the black and blue lines. Specify the year of the previous study.
Fig. 7. “Distance to the open ocean”. Pacific Ocean or Carribean Sea? Linear regression and coefficient of correlation must be indicated. “Depth” and “Distance to open ocean” are not “seagrass structural and elemental characteristics”.
Fig. 8. Poor quality. What does the color of the dots and lines mean?
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