ESSD-2025-207

 Long-term plankton and environmental monitoring dataset from the Marine Protected Area of the Iroise

Laetitia Drago et al.

GENERAL COMMENTS

This manuscript presents a valuable long-term dataset of phytoplankton (2010–2022) and zooplankton (2010–2023) collected across 15 stations in the Iroise Marine Natural Park, France’s first marine protected area, located off the coast of Brittany. The biological data are complemented by temperature and salinity measurements.

While this long-term dataset is highly valuable, its full potential is underutilized in the manuscript presentation due to the coarse taxonomic resolution applied (Table 3). The zooplankton classifications- limited to phylum (e.g., Cnidaria, Chaetognatha), class (e.g., Copepoda, Appendicularia), or occasionally order (e.g., Decapoda) - represent a significant reduction compared to the original EcoTaxa classifications. I would like to read -in the manuscript- some comments about this aspect. As a side note, I believe ZooScan/Ecotaxa have greater potential for taxonomic identification than what is reflected in the available dataset (Drago et al., 2025), especially when trained by an expert taxonomist.

In summary, I find the article suitable for supporting publication of the associated dataset, provided the suggested revisions are implemented. The dataset itself is valuable, demonstrating good quality and utility. My detailed review of the zooplankton component confirms its completeness, though the current organization should be improved to enhance reusability (as noted in my comments on Section 7). While the study is well-designed and generally clearly presented, several issues require attention to strengthen the manuscript for publication in ESSD.

 SPECIFIC COMMENTS

1. Introduction

This section provides a clear and well-structured background. I have suggested minor technical revisions in the corresponding section ("Technical Corrections").

A specific concern regards the imaging approach (Line 51). The claim that imaging methods allow for rapid processing of "large sample volumes" should be rephrased. A more accurate description would be that they enable "faster processing of more samples", which is distinct from handling larger individual volumes.

1. Study site

I find no issues with this section. Both the content and presentation are clear and well-structured.

1. Material and Methods

Some methodological clarifications are necessary. Please specify: (1) the criteria used for selecting sampling stations, and (2) the time required to complete all station sampling during each cruise.

The methodology for temperature measurements is unclear and contradictory. Lines 120–121 state that temperature was measured in water samples collected with Niskin bottles, stored in flasks, and analyzed on land—an unusual approach, as temperature is typically measured immediately onboard to prevent changes. However, Section 3.1.1 (line 127) mentions that temperature was measured using a WTW probe, with CTD sensors added in 2017 (line 129). This inconsistency is critical and requires thorough clarification.

The phytoplankton sampling method is not described. Additionally, it is unclear whether the shift to sampling at 15 m depth in 2016 (lines 131–132) replaced: only the near-bottom sampling, or both the sub-surface and near-bottom sampling. This ambiguity needs resolution.

There are inconsistencies regarding picoplankton analysis. The text states that "the employed methodology precluded identification and measurement of picophytoplankton" (line 166), yet Cyanobacteria (a picophytoplankton group) are later mentioned (lines 316, 320) and their abundances appear in Figures 4 and 5. This contradiction requires clarification (were Cyanobacteria quantified via a different method?).

For zooplankton collection, two key methodological details are missing: 1) was the deployed cable angle accounted for to accurately determine the sampled water layer height? 2) was the net thoroughly rinsed after retrieval to ensure all organisms were collected and none remained trapped in the mesh? These procedural details are essential for reproducibility and data reliability.

In zooplankton digitalization and identification, some details are missing:

-How many analysts processed the zooplankton samples? Were inter-calibration exercises conducted to ensure consistency, given potential operator bias during the sample fractionation and handling?

-Approximately how many organisms were analyzed per scanned sample?

-How were overlapping structures (e.g., copepod antennules) resolved during digitization?

I have a general concern regarding taxonomic resolution: why are large, distinct copepods (e.g., the Pontellidae female in Fig. 3A) only identified to the order Calanoida? Higher resolution seems feasible, since Pontellidae (as well as other calanoid families) are reported in the zooplankton dataset (Drago et al., 2025).

The review/validation of classified images was only applied to samples from 2018 onwards (lines 200–204, 256–259). What quality assurance measures were in place for pre-2018 data? This gap risks inconsistencies in the long-term dataset.

Figure 1 would benefit from an accurate revision. The map should be enhanced by 1) clear delineation of the boundaries of the Iroise MPA, 2) improved visibility of isobaths to better relate station positions to bathymetry, 3) inclusion of station B7 (mentioned in line 101 and figure caption), 4) accurate representation that transect B extends further north than transect D (line 102). Moreover, the background of temperature data should be removed as it represents results rather than methods, and the two 2016 snapshots are not representative for a long-term study.

1. Database structure and analysis

In this section (lines 265-294), the phytoplankton dataset should be presented as the first one, before zooplankton (second dataset), like it is presented in the methodological section and in sections 5.2 and 5.3.

For phytoplankton, the unit should be “cells/L”, not “individuals/L” (line 289 and somewhere else).

Phytoplankton cell concentration was considered for the surface and bottom abundance (lines 289, 290). What about the samples collected only at 15 m depth since 2016 (see line 132)?

1. Concluding remarks

It should be explained which were the “conditions” that were recorded to decrease in small pelagic fish (line 360).

Are there planktonic data in the Iroise Sea outside the MPA or in other Atlantic European MPAs that can be compared with the present dataset?

These datasets provide valuable opportunities for large-scale comparative studies and investigations of plankton dynamics in other MPAs, although the broad taxonomic classification may restrict some functional trait-based analyses (e.g., to size and biovolume structure).

1. Data availability (Plankton datasets)

The plankton abundance data are reported with inconsistent decimal precision (1–6 decimal places for zooplankton –file .csv; 0-3 decimal places for phytoplankton – file .csv). Consistency would improve clarity.

The taxon listing in the zooplankton dataset seems disorganized without a clear logical structure. For better usability, the taxa should be organized taxonomically (from Ctenophora to Tunicata), presenting species/genera/families in alphabetical order within their respective group (e.g., within copepods, or cladocera, or tunicates, etc….).

TECHNICAL CORRECTIONS

1. Introduction

The assertion in the first sentence is a well-documented and widely accepted knowledge in biological oceanography, so it does not need citation support. Moreover, the reference ‘Grigoratou’ (cited as ‘in press’ on line 33) is missing from the References section and thus inaccessible to readers.

L 35- Suggested change: ….this carbon passively through the sinking of molts, carcasses and fecal pellets, and actively through diel vertical migration…..

L36- Suggested change: At the base of aquatic…

L37- Suggested change: ….(e.g., Chavez…..

L43- Suggested change: …into plankton dynamics across…

L52,53- Remove repetition: “traditional taxonomic identification and novel trait-based analyses (Irisson et al., 2022; Orenstein et al., 2022).” is already said on line 48.

1. Material and Methods

L106- The three coastal stations should be named here and Fig 1 should be cited.

L109- It should be clarified what does it mean that two stations (Douarnenez and D1) were “treater together”.

L124, 125- “is” must be replaced by “was”.

L125- it must be clarified which depth is considered “subsurface”.

L127-129, 207- Temperature should be always mentioned before salinity for coherence.

L131- Suggested change: At the transect stations….

L132- Suggested change: At costal stations…

L133- Clarification: specify if the glass of the flask was dark.

L133-135- Suggested change: The present dataset comprises 785 phytoplankton samples in total (Fig. 2). Their number varied annually………………..conditions. The sampling effort increased notably from 2010 until a peak of 97 samples in 2017 and then gradually decreased to about 50 samples in 2022.

L149- Suggested change: ….57 cm mouth diameter…

L150- Suggested change:…was deployed vertically to a maximum depth……

L154- The “1:3 sample-to-formaldehyde ratio” here reported is wrong. It should be the opposite, i.e., 1:3 formaldehyde-to-sample ratio.

L154- a verb is missing: The annual number of zooplankton samples ranged from …

L155- It should be explained what exactly means “reflecting variations in sampling strategy”.

L159- Remove “then”

L166- “measurements” should be replaced by “counts”.

L173- Suggested change: sieving the samples through a 1000 μm mesh….

L179, 180- This info is already given on line 168. Repetitions should be removed.

L196- Remove: (J) Centropagidae

L197- Instead of “Podon”, this category should be better named Podonidae, because both Podon and Pleopis may occur in coastal zooplankton samples and their images are not easily distinguishable.

1. Data quality control

This section compiles information that has already been discussed in previous sections.

For example, on lines 252-254 (already on lines 159-161) and on lines 256-259 (already on lines 200-204). Repetitions should be removed.

1. Database structure and analysis

L296, 297- Suggested change: Figure 4 shows the mean annual phytoplankton abundances across the sampling area, highlighting the remarkable temporal and spatial variability throughout the study period. .

L298- Suggested change: ….and 2022 in transect B, with ….

L299- Suggested change: In transect D, remarkable abundance…..

L312, 313- Suggested change: In surface waters, the phytoplankton composition showed interannual and spatial variations along both transects.

L318- Suggested change:…coast-offshore gradient.

L344- Suggested change: …at offshore stations…

1. Concluding remarks

L365- Suggested change: …health in the Iroise Marine Natural Park. Beyond its ecological significance, this MPA and the Iroise Sea hold particular…..

Figure 2- In my opinion the last sentence is not appropriate in a figure caption, and it should be moved to the concluding section.

Figure 4- “Transect B” and “Transect D” should be indicated on the upper and lower panels, respectively

Figure 5- L324-326 (Each stacked bar….at that station) provide a redundant info with respect to line 324.

Table 3- Commas for decimals in the “%” column should be replaced by points.

Why some “annotation categories” are not considered in the “groups” column”? It seems that “nauplii<Crustacea”, “megalopa<Brachiura, “Ostracoda”, “Cirirpedia” - just to mention some categories as example- have not been included in the groups considered for the present dataset. If this is not the case, the names should be repeated in the “groups” column.

It should be said in the caption that the groups are listed in decreasing number of images

References

The following references seem incomplete. In some cases, the link should be provided.

Berthou et al, 2010

Chamberlain and Vanhoorne 2023

Duhamel et al., 2011

Picheral et al 2017

The key figure is well-designed, but station B7 (referenced in the text and included in Supplementary Table 1) is missing. Additionally, I recommend centering the inset map of France more effectively by shifting it slightly to the right, ensuring the full study area boundary is visible.

Supplementary Table 1

The legend for the orange and green colors used to highlight rows requires clarification. The term “classification” is ambiguous—does it refer to “taxonomic identification”? If so, this should be explicitly stated, as it is critical for dataset quality and reusability. Additionally, the specific inconsistency in classification (e.g., whether species were grouped at genus level, genera at family level, etc.) during some years should be clearly explained. For example, does orange indicate years where identifications were resolved only to higher taxonomic levels?

If the same color scheme applies to the “coastal station sampling plan”, the legend should also be included in the second sheet of the file.

Lastly, in the table caption, “Colored colors” should be corrected to “Colored cells”.

Supplementary Table 2

The profiles of turbidity, oxygen, fluorescence reported in this table are not mentioned in the text.

Supplementary Table 3

The Ecotaxa ID and the names of the projects would be more useful if accompanied by links that give access to the projects.

General comments:

This manuscript presents long-term phytoplankton and zooplankton monitoring data, with the associated environmental parameters, from the Iroise Marine Natural Park, Iroise Sea, a place of cultural and economic importance to France’s sardine fishery. These datasets were collected to support current and future studies into plankton community dynamics and biodiversity patterns in the Iroise Sea.  

While useful, this manuscript could be strengthened by improving on the taxonomic resolution of the identifications or an explanation of the reasoning behind the current resolution. Additional information could be provided to support some of the statements by the authors in regards to the background and importance of the area and the research conducted. Better connections could be built between the Introduction and Concluding Remarks to more comprehensively connect the paper together. Greater detail into the QA/QC procedures could be included, as well. Lastly, the Figure captions could be improved by removing some parts and unifying the text of others.  

In conclusion, I find the manuscript suitable for publication with the associated datasets, if the following issues are addressed prior to publication. 

Specific comments:

1. Introduction



Minor revisions suggested in “Technical Corrections” section. 

2. Study site



This section could be re-written to more clearly explain the scientific importance of the site. See “Technical Corrections”. 

3. Material and Methods

Line 113, Figure 1 caption: Not sure why the temperature data is included on these figures for the specific days. Differences between spring and summer? If it is relevant, it could be better explained why. Since the addition of temperature data represents only specific days, it is probably better removed. 

Lines 120-121: “Samples were promptly divided into flasks and delivered to IDHESA laboratory



(Brest site accreditation no. 1-1827 and Quimper site accreditation no. 1-1828) for analysis of temperature and salinity.”



Temperature was not measured immediately?

Line 164-165: “Taxonomic identification was performed to the lowest feasible level, …”



The data as presented in the manuscript shows only phylum-level. Why?

4. Data quality control

Lines 244-259: This whole section seems repetitive of previous information given.

6. Concluding remarks

Information from here could be used earlier. Minor revisions suggested in “Technical Corrections” section. 

Technical corrections:

Line 33: “… marine and freshwater ecosystems (Grigoratou, in press).” 



Please update the reference now that this article is published. 



Grigoratou, M., Menden-Deuer, S., McQuatters-Gollop, A., Arhonditsis, G., Artigas, L. F., Ayata, S.-D., Bedikoğlu, D., Beisner, B., Chen, B., Davies, C., Diarra, L., Elegbeleye, O., Everett, J., Garcia, T., Gentleman, W., Gonçalves, R., Guy-Haim, T., Halfter, S., and Hinners, J.: The immeasurable value of plankton to humanity, BioScience, biaf049, https://doi.org/10.1093/biosci/biaf049, 2025.

Line 34: (Simon et al., 2008). 



Is there a more recent reference?

Line 38: “… with substantial economic implications.” 



Please mention one or two of these implications. 

Line 49: “… providing unprecedented views into the diversity and distribution of zooplankton and phytoplankton.”  



Add a line about what the diversity and distribution of plankton can tell us.

Line 59: “… significant challenges remain …” 



Provide an example(s) of the challenges. 

Line 77-79: “The MPA’s monitoring activities align with two major European directives: the Water Framework Directive (WFD/DCE) for coastal waters and the Marine Strategy Framework Directive (MSFD/DCSMM) which aims to achieve Good Environmental Status of marine waters.” 



Please reference the policy instruments.

Line 81-83: “Their monitoring is particularly relevant for MPAs like the Iroise Marine Natural Park, as the rapid responses of these organisms to environmental changes can serve as early warning signals of ecosystem shifts.” 



How are the early warning signals relevant to the Iroise Marine Natural Park in particular? As the sentence is written, the first half of the sentence and second half don't relate.

Line 83: “It is also particularly relevant for fisheries …” 



How fisheries relate to the MPA could be more clearly explained. 

Line 85: “The Iroise area also serves as a natural laboratory …” for what? 

Line 90-94: Moving these two sentences earlier in the paragraph would answer earlier questions. 

Lines 81-94 could be re-written for clarity and taking into account the comments made in the Concluding Remarks.

Line 104: “(See Supplementary Table 1).” 



Suggest adding "Transect sampling plan" for clarity, since there are two sheets in the Excel.

Line 105: “Since that year, the sampling frequency has … “



Suggest "From 2017 until 2023, the sampling frequency increased from three to ...."



Perhaps mention that in 2020, sampling frequency was only three times and why. 

Line 106-107: “… every month (Supplementary Table 2).” 



Suggest adding "...across the indicated time periods in Supplementary Table 2."

Lines 107-108: “The highly variable weather of the region occasionally prevented comprehensive sampling of hydrobiological variables and plankton at all stations.”



Could this be connected to the comment at Line 105. Could also add “.."such as in 2020 ...", if they are connected.  

Lines 119-120: “… following the Service d’Observation en Milieu LITtoral (SOMLIT) (Cocquempot et al., 2019) and Institut Universitaire 120 Européen de la Mer (IUEM) protocols.” 



Might be worth briefly summarizing these protocols. Or are the protocols what is explained in 3.1.1-3 below?

Lines 131, 132, 149: Replace “was” with “were” for agreement across paragraphs. 

Line 144-145: “Indeed, the funding agency needed to be reassured on the fact that collecting this data was useful given its cost.” 



These two sentences should be removed and developed further in Concluding Remarks (see next comment as well). Suggest: “The funding agency needed to be reassured that collecting this data was useful given its cost.” Does “this data” refer to both phyto and zoo? Or just zooplankton data? Please clarify. 



Please clarify that the collection went ahead by other methods? Or went ahead with reduced effort? 2014 is not included in the Supplementary files sampling plans, but some sampling data is included in Figure 2. 

Line 145-146: “Publishing such datasets in open access is then a way to reassure the funders that collecting such datasets is indeed useful for the scientific community.”



Could remove this sentence and develop this point more fully in the Concluding Remarks. Add here, “See Concluding Remarks.” 



Or alternatively, could say something along the lines of “Sampling was (suspended/reduced) in 2014, then resumed in 2015 after reassuring the funders of the utility of this data. See Concluding Remarks.”

Line 165-166: “… generally identified to genus and species.”



Suggest “generally identified to genus or species.”

Line 212 – is the renaming of the station relevant here? Does it appear elsewhere in the ms or appendices? If not, suggest deletion of line. If so, please link more clearly. 

Line 221: is it ‘Ecotaxa’ or ‘Ecostaxa’?

Line 251: “… removal based on a 0.001 quantile threshold.” 



This was not mentioned earlier in section 3.3.1. 

Line 254: Is Beatriz part of NMBAQC or any similar QA/QC programmes? Yes, consistency is good with one analyst, but what about checking accuracy of taxonomic ID? How is that accounted for?

Line 262-263: “This temporal heterogeneity in sampling effort should be considered when interpreting long-term trends in plankton communities from this dataset.”



Possible influences of this heterogeneity on interpretation?

Line 292: “(Chamberlain and Vanhoorne., 2023).”



Remove the “.” after Vanhoorne. 

Line 301-302: “Interestingly, there does not appear to be a consistent coastal-to-offshore gradient in phytoplankton abundance throughout the years in either northern and southern stations.”



Remove "Interestingly"; tell us why it is interesting or what can be interpreted from this lack of consistent gradient.

Lines 307-308, Figure 4 : “… with different colours indicating the absolute abundance of each phylum.”



Suggest “… with the size of each coloured bar indicating …” for clarity, especially since the last sentence of the caption says “Each phylum is represented by a distinct colour …”

Lines 323-326: There is some repetition in the first and second sentence that can be combined for clarity. 

Lines 327-328, Figure 5: “Each phylum is represented by a distinct colour.” 



Suggest the same as in Figure 4 caption, “Each phylum is represented by a distinct colour as shown in the legend.”

Figures: Figure 5,6 and 7: x axis labels are not legible. Can you maybe move the legend to underneath the graphs, allowing more space for the labels? 

Line 340: “… as it only contains 3 images.”



Suggest “… as it contains only 3 images.”

Line 341: “The zooplankton community shows clear spatial gradients in dominant groups (Fig. 7).”



Does this tell us anything in particular?

Lines 350-356: In this caption, there is some repetition in describing the Figure. Suggest combining or eliminating parts of the first and second sentences, with the fourth sentence. 

Line 354, Figure 7: Line 340: “… as it only contains 3 images.”



Suggest “… as it contains only 3 images.”

Line 357, Figure 7: “Each faunistical group is represented by a distinct colour.”



Suggest the same as in Figure 4 and 5 captions, “Each phylum is represented by a distinct colour as shown in the legend.”

Lines 360-362: “... highlighting the critical importance of long-term monitoring of plankton communities (Holland et al., 2025) which constitute their primary food resource (Brosset et al., 2016; Sommer et al., 2018).”



This point could be made much more strongly in the previous sections and explicitly reinforced between lines 80-95.

Lines 367-369: “This makes the long-term monitoring of plankton communities crucial not only for biodiversity conservation but also for preserving the economic and cultural heritage that led to its designation as France's first Marine Protected Area.”



This point as well could be made more explicit earlier in the text, such as between lines 80-95.

Line 371: Again, but how is the analyst’s work QA/QCed?

Key Figure

The inset boundary appears to cut off the study area. 

Supplementary Table 1

It is unclear what the colour scheme means. 

Supplementary Table 2

Supplementary Table 3

It would be useful to include links to the Ecotaxa projects.