the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 31 Mar 2025
Long-Term Monitoring of Hydrological Dynamics and Phytoplankton Biomass Indicator in Three Shellfish Ecosystems of the English Channel (2000–2024)
Abstract. This study investigates the long-term monitoring of physico-chemical parameters and biogeochemical cycles in coastal ecosystems, focusing on three stations in Normandy: Blainville-sur-Mer, Saint-Vaast-la-Hougue, and Utah Beach. Over a 24-year period, we analyzed trends in temperature, pH, chlorophyll a concentrations, and nutrient levels, aiming to assess the impacts of climate change and human activities on marine ecosystems. Results show a consistent rise in winter temperatures, particularly since 2013, alongside increasing ocean acidification, especially at Blainville-sur-Mer. These trends suggest potential consequences for planktonic communities and mollusk health. Nutrient analysis revealed significant variations, including high ammonium concentrations on the East coast and a gradual decline in phosphates over the last 15 years, highlighting the influence of anthropogenic activities. The study also identified nutrient limitations, with phosphorus dominating the East coast and nitrogen on the West coast. Our findings emphasize the need for effective nutrient management strategies to mitigate the effects of climate change and human impact, ensuring the sustainability of coastal ecosystems and aquaculture practices. This long-term monitoring is crucial for understanding ecological dynamics and guiding future coastal zone management in the face of global environmental changes.
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RC1: 'Comment on essd-2025-155', Anonymous Referee #1, 04 Jun 2025
The manuscript is currently more in the format of a conventional research paper rather than a data paper, with an extended analysis of the results and discussion but . My review follows responses to the questions asked in the reviewer guidelines:
1. Read the manuscript: are the data and methods presented new? Is there any potential of the data being useful in the future? Are methods and materials described in sufficient detail? Are any references/citations to other data sets or articles missing or inappropriate?
Is the article itself appropriate to support the publication of a data set?
2. Check the data quality: is the data set accessible via the given identifier? Is the data set complete? Are error estimates and sources of errors given (and discussed in the article)? Are the accuracy, calibration, processing, etc. state of the art? Are common standards used for comparison?
Is the data set significant – unique, useful, and complete?
My response:
The methods are not new but the dataset is being made publicly available. The data are hosted on Zenodo (link provided in the manuscript) and are accessible. The data are potentially useful in the future but there are insufficient details given in the methods to allow other researchers to re-use the data. It is not possible to assess the data quality as there is insufficient information given. For example:
Chlorophyll: no information about the filter papers used, how the samples were stored and for how long before analysis, extraction method, references for analysis.
Nutrients: how were samples processed (e.g. were they filtered) and how were they stored before analysis and for how long?
pH: method needs further information including how samples were collected and handled before analysis, how long between sample collection and analysis, details for method of analysis, pH scale being used (e.g. total hydrogen scale, seawater scale, NBS) references for analysis.
YSI sonde: Give details of calibration e.g. were the temperature and salinity probes calibrated? If so, how and with what frequency? What is the unit used for salinity?
For all determinands: were certified reference materials also run for any of the parameters? If so, give details. Need to provide information about limits of detection, accuracy and precision for each of the parameters measured
Error estimates and sources of error are not presented or discussed. There is no mention of standards used for comparison.
The data are accessible in an Excel file via the Zenodo link provided. There are many values highlighted in different colours in the sheet but there is no information about what this means e.g. do any of these colours relate to quality flags? There are no descriptions of column headers within the file so the reader has to decide what each one means. There are no units associated with each parameter in the file.
3. Consider article and data set: are there any inconsistencies within these, implausible assertions or data, or noticeable problems which would suggest the data are erroneous (or worse). If possible, apply tests (e.g. statistics). Unusual formats or other circumstances which impede such tests in your discipline may raise suspicion.
Is the data set itself of high quality?
My response:
The data are made available through Excel but there is insufficient information regarding units and header descriptions for the data to be used. There is insufficient information provided to assess the quality of the data.
4. Check the presentation quality: is the data set usable in its current format and size? Are the formal metadata appropriate? Check the publication: is the length of the article appropriate? Is the overall structure of the article well structured and clear? Is the language consistent and precise? Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Are figures and tables correct and of high quality?
Is the data set publication, as submitted, of high quality?
My response:
There is insufficient information regarding units and header descriptions for the data to be used. There is insufficient information provided to assess the quality of the data.
Figures are directly from an R package and contain a lot of unnecessary text (e.g. titles in each sub plot) which make them very cluttered, difficult to read and make the actual plots too small. Legends are repeated in each sub plot of a figure. The place names Saint-Vaast-la-Hogue and Tocquaise are given for the same location – only one should be used throughout the text and figures as it adds confusion to use both.
I have attached an annotated pdf with my comments. If the paper is to be published as a data paper there needs to be the necessary method and QC details and analysis of data quality which are not currently provided. There is currently no analysis and discussion of the quality of the data.
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RC2: 'Comment on essd-2025-155', Sébastien Lefebvre, 26 Jun 2025
This is a very interesting database that has strong potential for publication. I have added specific comments and suggestions for improvements:
Introduction and Discussion: It would be valuable to emphasize the significance of this database compared to other long‑term survey efforts, such as the SOMLIT program in France (see Goberville et al., 2010 and the SOMLIT website). The strength of the present dataset lies in its high quality and regional scale, allowing comparisons across ecosystems with differing dynamics (e.g., the Bay of Seine vs. the Normanno‑Breton Gulf; see Dauvin, 2012, https://doi.org/10.1016/j.marpolbul.2011.12.010). It would also be worth mentioning if connections can be made with existing aquaculture databases from the same area.
Terminology: Replace the term “nutrient salts” (not common) with “dissolved nutrients” and ensure this terminology is used consistently throughout the manuscript.
Methods : Please justify why three stations were selected from the available six, and why certain variables were chosen for analysis. An explanation could be that these stations were used as examples to highlight specific patterns, but this needs to be stated clearly. Develop the section 2.3: further to clearly describe the statistical methods and functions used, especially for the time‑series analyses.
Results: Consider adding or discussing a PCA conducted on seasonally detrended data to strengthen the presentation of results (see Goberville et al., 2010). Figure 7: The legend and axis labels are too small and should be enlarged for readability. Table 2: The three sites differ primarily in the periods where P < Si < N and N < Si < P occur. The differences between Saint‑Vaast‑la‑Hougue and Utah are very slight, and this should be emphasized in the text (Section 3.4).
Discussion: The trend of decreasing dissolved nutrients (including silicate, which is not directly influenced by human activity) suggests that freshwater inputs have decreased over the study period, potentially due to reduced river discharge. Climate change and shifts in precipitation patterns could be significant drivers of these observations and deserve stronger discussion. Lower agricultural inputs could be part of the explanation but only for N and P. The discussion on changes in the phytoplankton community is speculative given the available dataset. Without supporting data, this section (particularly the references to Mangala) should be removed or significantly revised.
Citation: https://doi.org/10.5194/essd-2025-155-RC2 -
EC1: 'Comment on essd-2025-155', Sabine Schmidt, 06 Jul 2025
Dear co-authors
I urge you to take the comments of the two reviewers seriously. Both consider the dataset to be of interest. However, they both agree that a better description of how the dataset was collected and qualified is needed to enable it to be reused. I therefore urge you to thoroughly revise the way the dataset is presented.
Citation: https://doi.org/10.5194/essd-2025-155-EC1 -
AC1: 'Comment on essd-2025-155', Julia Sosinski, 20 Jul 2025
We would like to thank the reviewers and editor for their constructive and insightful comments. Their feedback has been extremely helpful in improving the quality and clarity of our manuscript and dataset. Below, we summarize the main changes made in response to the reviews.
**1. Materials and Methods – Data acquisition and quality control:**
We have substantially revised the *Materials and Methods* section to include detailed protocols for all measured parameters.
- **Chlorophyll a** concentrations were determined following filtration of three 100 mL aliquots through Whatman GF/F glass fiber filters (nominal pore size 0.7 µm). Filters were stored frozen at −20 °C and extracted in 90% acetone for 12–24 h in the dark at 4 °C. Measurements were performed using a Turner Designs fluorometer, following the method described by Strickland & Parsons (1972). Results are expressed in µg L⁻¹.
- **Dissolved nutrients** (NH₄⁺, NO₂⁻, NO₃⁻, PO₄³⁻, and Si(OH)₄) were measured via spectrophotometry. At the time of collection, samples were pre-filtered through a 50 µm mesh filter mounted directly on the Niskin bottle to remove large particles. After collection, samples were centrifuged at 4200 rpm for 10 minutes to remove residual suspended matter, ensuring that only the dissolved fraction was analyzed. Samples were kept at 4 °C in the dark and analyzed within 4 hours of collection to prevent degradation.
- **In situ temperature and salinity** were recorded using a YSI 6600 multi-parameter sonde, calibrated before each field campaign according to the manufacturer's instructions. Salinity calibration used certified NaCl standards (35 PSU). The accuracy of the salinity sensor was ±0.1 PSU and ±0.15 °C for temperature. Barometric pressure compensation was systematically verified.
- **pH** was measured in the laboratory using a Mettler Toledo F2 pH meter with a LE420 glass electrode. The instrument was calibrated daily using standard buffer solutions (pH 4.00, 7.00, and 10.00 at 20 °C). Measurements were conducted at a controlled temperature of 20 °C, on the NBS scale, without CO₂ equilibration. Water samples were stored in the dark at 4 °C and analyzed within 4 hours.
- For all parameters, details on accuracy, precision, and detection limits have been added in the revised manuscript. Where possible, certified reference materials were used.
**2. Dataset format and metadata:**
We have revised the dataset hosted on Zenodo to improve usability and transparency:
- Column headers now include full variable names and units.
- A separate sheet provides a detailed variable dictionary, including methods and units.
**3. Justification of station and variable selection:**
We clarified in Section 2.1 that the three stations were selected. These stations were chosen primarily because they offer the most complete and continuous datasets since the beginning of the monitoring program in 2000, ensuring the robustness and reliability of long-term analyses. In addition to their data quality, these sites represent contrasting environmental conditions that allow for the exploration of a representative gradient along the Normandy coastline.
**4. Statistical analysis – PCA and time-series methods:**
Following RC2’s suggestion, we developed Section 2.3 to better explain the statistical approach. We performed Principal Component Analyses (PCA) on seasonally detrended data.
**5. Figures and terminology:**
All figures have been redesigned to improve clarity:
- Font sizes and axis labels were enlarged.
- Redundant legends and subplot titles were removed.
- The confusion between “Tocquaise” and “Saint-Vaast-la-Hougue” was resolved. Only one name is now used consistently throughout the manuscript and figures.
**6. Discussion – Clarifications and removals:**
We revised the discussion to better reflect the dataset’s scope:
- The speculative section on phytoplankton community shifts (including the reference to Mangala) has been removed.
- We expanded the discussion on the observed decrease in dissolved nutrient concentrations. We now consider plausible explanations including reduced river discharge, climate change, shifts in precipitation, and decreasing agricultural inputs (mainly for N and P). The case of silicates, less directly influenced by human activity, is discussed with reference to hydrological changes.
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We hope these substantial revisions meet the expectations of the reviewers and the editor, and we remain available for any additional improvements needed.
Sincerely,
Sosinski Julia
On behalf of all co-authors
Citation: https://doi.org/10.5194/essd-2025-155-AC1 -
EC2: 'Reply on AC1', Sabine Schmidt, 20 Jul 2025
I encourage you to submit rapdily the revised version of your article that incorporates the reviewers' comments, as detailed in your response. I look forward to receiving the new version.
Citation: https://doi.org/10.5194/essd-2025-155-EC2
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EC2: 'Reply on AC1', Sabine Schmidt, 20 Jul 2025
Data sets
Hydrobiological Data from 6 Stations of the HYDRONOR Observatory (2000 - 2024) Julia Sosinski et al. https://zenodo.org/records/15058836
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