Continuous Zonal Gradients Characterize Epipelagic Plankton Assemblages and Hydrography in the Subtropical North Atlantic
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Review for the paper "Continuous zonal gradients characterize epipelagic plankton assemblages and hydrography in the subtropical North Atlantic" by Antonio Bode, M. Ángeles Louro, Elena Rey, Ángel F. Lamas submitted to "Oceans".
General comment.
Plankton assemblages play a critical role in various ecological and biogeochemical processes. The impact of global natural changes on these communities can lead to significant alterations in global biogeochemical cycles, ecosystem functioning, and predator-prey interactions, ultimately resulting in trophic changes. While there has been notable progress in studying plankton in the North Atlantic, certain areas require further attention. Specifically, our understanding of large-scale variations in plankton in tropical regions remains limited. To address this knowledge gap, the authors conducted a comprehensive study aimed at elucidating how environmental gradients influence plankton abundance and composition along a transect crossing the Atlantic Ocean at 24°N. The study revealed significant spatial differences in hydrological gradients and various planktonic variables. This research provides an informative snapshot of environmental-plankton datasets and holds promise for future monitoring studies. However, there are some issues that need to be addressed before the paper can be accepted. To enhance the visualization of the main findings, I would recommend incorporating additional analyses. These analyses could further illuminate the observed spatial differences in the hydrological gradients and the influence of these gradients on plankton abundance and composition.
Major Points:
1. Introduction: The goal of the study should be clearly stated and the description of plankton assemblages should be expanded to include the analysis of relationships between plankton and the environment.
2. Material and Methods: The authors should provide data on the environmental conditions in the study region. Additionally, a brief overview of the ecosystems in the study area would be beneficial for readers to better understand the environmental context in which the study was conducted.
3. Material and Methods: It is recommended to include a detailed description of the methods used to process and treat phytoplankton, microplankton, and zooplankton samples. This information will enhance the reproducibility of the study and provide transparency in the methodology.
4. Results: It is suggested to perform an analysis to investigate the community structure of mesozooplankton. Cluster analysis could be a relevant tool to visualize the structure of mesozooplankton assemblages. This additional analysis will provide valuable insights into the organization and composition of mesozooplankton communities, further enhancing the understanding of plankton dynamics in the study area.
5. Results: Comparing plankton between two provinces, the North Atlantic Subtropical West (NASW) and the North Atlantic Subtropical East (NASE), would be a valuable addition to the study. This comparison will enable the examination of potential differences in planktonic communities and their responses to environmental gradients within different regions of the North Atlantic Subtropical zone.
6. Discussion: The authors should provide additional data regarding phytoplankton blooms in the study region. Given the use of fine nets for collecting micro- and phytoplankton, it is essential to justify that all organisms were quantitatively captured. If there were phytoplankton blooms across the transect, the nets may have become clogged, potentially leading to an underestimation of plankton abundance. Regardless of the presence or absence of blooms, this potential limitation should be acknowledged in the discussion section. Additionally, since sampling was conducted during sunlight hours (10:00-16:00) in the upper 200-m layer, it is important to consider that some zooplankton populations might have been under-sampled due to diel vertical migrations. This limitation should also be addressed and discussed in the manuscript.
7. Please include a conclusion that summarizes the main findings of the study. The conclusion should provide a concise overview of the key results and their significance in the broader context of plankton research.
Specific remarks.
L85. Consider replacing "were collected busing" with "were collected using".
Table 1. Consider replacing "calanoida", "eufausiacea", "decapoda", "foraminifera" with "Calanoida", "Euphausiacea", "Decapoda", "Foraminifera".
L210. Consider replacing "eufausiacea" with "Euphausiacea".
Comments on the Quality of English Language
Minor revision.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
The authors investigated the hydrology and plankton composition of the North Atlantic subtropical waters from east to west. Generally speaking, the author has done a good job of statistical analysis and discussion in this manuscript. However, I have a few suggestions for the author to revise this manuscript before it can be considered for publication.
1. Please provide hydrological profiles of all stations (from east to west), including temperature, salinity, chlorophyll concentration, nutrients, etc. This will facilitate the readers to understand the various environmental parameters during the study period. And indicate the depths of DCM and MLD in the contour plots.
2. The Figure S1 should be included in this manuscript.
3. How is the POC of each particle in the Figure S1 determined? This should be written in the Materials and Methods. Also, why use area instead of volume?
4. Line 304-318. “Such hydrographic and biogeochemical heterogeneity is consistent with our findings of non-linear gradients……” In addition to temperature and salinity, should other factors be considered? For example, nutrients. Ekman pumping has the potential to bring deep nutrients to surface waters. Evaporation or rainfall may affect the nutrient concentration in the surface water. In addition, nutrient changes in NASE should be influenced by dust storms from the Sahara Desert. I suggest that the authors discuss these factors' potential impacts on plankton community composition in this area.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
L. 28 – "N Atlantic" – this notation confuses a little, because the chemical element nitrogen (N) is mentioned later. I recommend either use full word, or explain this abbreviation on the first use.
L. 80 – "167 stations where occupied…" – maybe better "we made detailed CTD profiles between the surface and ca. 5000 m on 167 stations with a CTD-rosette system equipped with conductivity, salinity, depth and chlorophyll fluorescence sensors".
L. 82 – "From this study…" – "For…"
L. 85 – "busing a net …" – "using".
L. 85-86 – Nets of what types were used?
L. 86-87 – Plankton samples were preserved in formaldehyde – both, zoo- and phyto?
L. 102 – How were categorized other groups of phytoplankton (Chlorophyta, Euglenophyta, Cryptista etc.) if they were determined at all?
L. 114-115 – "taxonomic identification … was determined" – "taxonomic composition of zooplankton was determined…".
L. 130-131 – The verb is absent.
Fig. 3 – The Y axis of the Depth of chlorophyll maximum would be more natural in reversed scaling.
L. 200-201 – "Fig. 5" –> "Fig. 6"
L. 307 – "eddie" – "eddy"
L. 316 – "SCM" – must be "DCM"?
L. 341 – "though" – "through"
L. 363-370 – The explanation of non-linear gradients of hydrological parameters and linear gradients of planktonic characteristics is somewhat unclear. Why non-linear environmental gradients would be levelled out by individual species? What is the role of species' niches partition? It is difficult to conceive without addressing the cited paper. Please clarify this.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
Accept
Comments on the Quality of English Language
Minor revision
Reviewer 2 Report
Comments and Suggestions for Authors
The authors have done an excellent revision. I have no more questions or suggestions. I recommend this manuscript be considered for publication in this journal.
Reviewer 3 Report
Comments and Suggestions for Authors
I am satisfied with the authors' answers. Iam sure the paper is ready for publication in the present form.
