Spectral Characteristics of Beached Sargassum in Response to Drying and Decay over Time

Round 1

Reviewer 1 Report

This contribution is a concise methodology study of the ability to discriminate fresh Sargassum from its decayed state using spectral remote sensing. Presumably, the goal of this study is to demonstrate that using large-scale satellite data would be worthwhile although the methods used in the paper are near-surface in situ and mesocosm experiments. The paper is a solid contribution and methodologically sound, but I feel that it's impact is limited by the lack of even a preliminary comparison of their in situ data to any satellite imagery. As a result, the conclusions are more limited in their applicability and much more speculative - in terms of application to large-scale satellite RS data - than such a study ideally would be. My opinion is that this paper is publishable, but perhaps not as significant or impactful as it could be if even one satellite image from e.g. Sentinel-2 could be used.

My other comments are minor suggestions. Figure 3 would benefit from a caption that tells the reader that colors are by elapsed time from fresh (purple) to decayed (or dry?) in yellow.  Figure 4, the acronym ASD needs to be defined in the caption and the gray lines are difficult to see (replace with black lines). Figure 5 refers to an A and B in the caption that doesn't seem to be included in the figure, and how the lines shown in Figure 5 relate to Figure 3 is unclear. Finally, I suggest including Figure S1 as part of the main paper around Line 132. This would add value to the paper, and it is necessary to demonstrate the soundness of the methodology.

Pending very minor improvements, I recommend publication of this work.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The author demonstrated, through both outdoor and indoor experiments, that there are significant differences in the spectral reflectance between fresh and decomposed seaweed. This could potentially be observed using Planet Scope and Sentinel-2 for monitoring purposes.

The following are the opinions and suggestions for this article:

The data collection procedures in Section 2.2 lack details on several aspects, including the calibration plate used for correcting measurement angles in the spectrometer, as well as the time interval for collecting dark current readings.

In line 119,“The condition of Sargassum was visually assessed to locate samples within four different states: fresh, dry, mixed...” it would be more accurate to describe the state of the seaweed using quantitative parameters such as drying time, length, or pigment content.

(https://doi.org/10.3390/rs14020346 and ttps://doi.org/10.3390/s22134656)

The description of time in lines 138-139 doesn't mention the time zone.

In line 141,“we found changeable weather conditions did not appear to have a large impact on the spectral response (Figure S2)”, it would be more appropriate to use quantitative and statistical measures to indicate the differences between them, such as one-way analysis of variance (ANOVA).

In lines 148-156, relevant manuscripts should be cited to explain why current temperature, measurement time, and measurement time interval were chosen.

Considering the context in the following lines, "Planet" should be changed to "Planet Scope" in line 166 to avoid ambiguity.

The results did not mention the use of Principal Component Analysis (PCA) in lines 170-173.

To improve readability, it is recommended to add a vertical line as highlighted in Figure 4 or label the visible light range in the figure, as mentioned in line 179.“As Sargassum dries or decays, the...”

Section 3.2 utilized an indoor experimental setup while Section 3.1 was conducted outdoors, resulting in mismatched wavelength ranges between the two experiments. It may be helpful to provide an explanation for why a single spectrophotometer was not employed throughout both experiments.

Section 3.3 is the pivotal point of this thesis as it presents the J-M distance and transformed divergence (TD) with values ranging between 0 to 2. Two samples are considered substantially separated if both the J-M distance and transformed divergence exceed 1.9. However, if these values are less than 1.8, additional adjustments may be necessary as the degree of separation is insignificant. In cases where the value is less than 1, merging the two sample classes should be considered.

I strongly recommend adding transfer separation degree to increase persuasion, and adding horizontal lines at positions 1.8, 1.9, and 1.0 on the y-axis in Figure 4.

In lines 224-226 and 269, “The coloured vertical...”, the processing of hyperspectral data for Planet Scope and Sentinel-2 is mentioned, but it is unclear whether the data was resampled using response functions from the two satellites before analysis or if only the spectral range of the response function was used for analysis.

To enhance the discussion, it may be beneficial to include additional studies related to seaweed physiological ecology, as well as examples from real-world applications of algal research conducted in coastal areas, such as those presented in publications https://doi.org/10.1002/rse2.327.

Regarding the images, lines 212-218 mention "Figure 5" but its location should come after Figure 4. Additionally, it may be helpful to adjust the order of C and A before zooming in on specific areas in Figure 1 to display the general range first.

The Figure 1 should be placed after the first paragraph of Section 2.1 (between lines 92 and 93).

Lines 110-115 should be included in Section 2.1.

In summary, I believe that major revisions should be made to this article.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Spectral characteristics of beached Sargassum in response to 2 drying and decay over time provide a significant contribution to the problem of pelagic Sargassum bloom. Beached vegetal biomasses is impacting coastal ecosystems and economy due to questionable management option.  Spectral response of fresh and decay Sargassum improve the understating of natural processes and have many application to monitoring and management strategies necessary to remove material from beaches. English level is fine and figures are clear.

The major limitation of the present paper is the limited reference list (see scopus export file into folder). Unfortunately, the publication does not take into account many publications of scientific community which should be cited and also discussed in order to comment results and the implications on other research topics.

The risk is that this well-presented spectral library is not eligible for publication in a high-impact factor journal such as remote sensing without a deeper evaluation at local and international level.

Some improvement can also be done in terms of structure/organization of the paper and supplementary material in order to improve the readability of the paper.   

Finally, some detail revisions are listed as follow:

Line 58: please add some references related to seagrass or Sargassum management. There is a huge literature about seagrass wrack in the Mediterranean Sea for example.

Line 113: it should be better to insert table 1 and remove it from SM

Line 114: Figure 1b is missing. Is it possible to prepare figure 1 (a, b, c) on vertical instead horizontal ?

Line 132: it should be better to insert S1 and remove it from SM

Line 142: it should be better to insert S2 and remove it from SM

Line 213: in Figure 5 the letter b is not indicated

Line 227-228: Correct figure 5

Comments for author File: Comments.zip

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have revised and improved the manuscript. It is recommended to be accepted for publication.

Author Response

Thank you

Reviewer 3 Report

changes made are not many, but the article seems improved.

the references, at the end of the text, is still partially inconsistent and does not always comply with the journal's rules.

Author Response

Thank you.

The reference list has been modified and this new version of the manuscript will be uploaded.