Sub-frontal niches of plankton communities driven by transport and trophic interactions at ocean fronts
Abstract. Observations and theory have suggested that ocean fronts are ecological hotspots, associated with higher diversity and biomass across many trophic levels. The hypothesis that these hotspots are driven by frontal nutrient injections is seemingly supported by the frequent observation of opportunistic diatoms at fronts, but the behavior of the rest of the plankton community is largely unknown. Here we investigate the organization of planktonic communities across fronts by analyzing 8 high resolution transects in the California Current Ecosystem containing extensive data for 24 groups of bacteria, phytoplankton and zooplankton. We find that a distinct frontal plankton community characterized by enhanced biomass of not only diatoms and copepods but many other groups of plankton such as chaetognaths, rhizarians and appendicularians emerges over most fronts. Importantly, we find spatial variability at a finer scale (typically 1–5 km) than the width of the front itself (typically 10–30 km) with peaks of different plankton taxa at different locations across the width of a front. Our results suggest that multiple processes, including horizontal stirring and biotic interactions, are responsible for creating this fine-scale patchiness.
Inès Mangolte et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2023-471', Anonymous Referee #1, 06 Apr 2023
- AC1: 'Reply on RC1', Ines Mangolte, 10 May 2023
RC2: 'Comment on egusphere-2023-471', Anonymous Referee #2, 28 Apr 2023
- AC2: 'Reply on RC2', Ines Mangolte, 10 May 2023
Inès Mangolte et al.
CCE-fronts code and data https://zenodo.org/record/7734963
CCE-fronts A https://doi.org/10.5446/61004
CCE-fronts C https://doi.org/10.5446/61005
CCE-fronts E https://doi.org/10.5446/61006
CCE-fronts F https://doi.org/10.5446/61007
Inès Mangolte et al.
Viewed (geographical distribution)
The manuscript of Mangolte et al. constitutes an interesting analysis on plankton communities dynamics in response to a frontal region in the California Current. As explain by the authors, although fronts are well known to be ecological hotspots with high plankton diversity due to the injection of nutrients into the euphotic layer, the mechanisms between nutrient supply and higher trophic levels is still poorly understood. Furthermore, the impacts of the fronts on plankton distribution and on the behavior of the plankton communities have been scarcely studied in situ. Since several years, researchers have fully realized the significance of this problem, but limited by the observation means (especially biological parameters), the current understanding is very limited.
Based on these backgrounds, I think this work is a very good attempt.
In this study, in situ datasets were achieved during several cruises lead in the California Current between 2008 and 2017 with a similar sampling methodology consisting to perform CTD stations spaced at high resolution along transects across frontal structures. These fronts have been identified thanks to satellite observations and the use of a MVP. Plankton samples were analyzed post cruises with 3 methods : flow cytometry, HPLC and ZooScan. This methodology is clear. The identification of frontal structures is well supported by supplementary information in Appendix.
The authors used these large datasets to study the response of plankton communities (in term of biomass and taxonomy) to frontal dynamics. Generally, the results are fairly well presented and are interpreted appropriately in the discussion.
In the conclusion, the authors are well aware of the limitations of their method and in particular they highlighted the importance of leading Lagrangian cruises with instruments able to sample at high temporal and spatial resolution the physical and biological variables. This part could be improved. Indeed, it lacks a bit of connection with the context and the scientific questions developed in the introduction.
The appendix section is very supplied with figures. Although these results are interesting, the authors should consider if all of them are really relevant. Indeed, in my opinion the total number of additional figures is excessive.
Finally, for me the grammar is ok, but I am not a native English speaker, that is why I let the English editing service check.
I recommend the manuscript for minor revisions prior to publication in Biogeosciences.
After a concise presentation of the context of this study (i.e., fronts and their potential impact on plankton), the authors have well exposed their hypothesis based on the work of Lévy et al., 2018 as well as their scientific questions. Then, the authors provided a short description of the region studied and introduced the CCE-LTER program and cruises during which the data were acquired.
However, the end of the Introduction (Ln 52-63) is a little confusing, with a lot of information. The information is relevant, although the more technical details should be indicated in the methodology. I think this last paragraph should be simplified. Based on the objectives that the authors have previously defined, they can just briefly explain how they would answer them.
Ln 12 : I understand that it is an introductory sentence for open your Introduction, but can you provide some references.
Ln 43 : Do not write in italics “California Current Ecosystem”.
Ln 48 : Define the acronym SSH as Sea Surface Height.
Ln 52 : Here there is a change of topic, please, start a new paragraph.
Ln 52-53 : “The empirical measurements [...]” : This sentence should be in the methodology section.
Ln 54 : Move “(with a spacing of 1 to 5 km between stations)” in the methodology section (Ln 68).
Ln 55-61 : “We identified [...], We first investigate [...], We find [...], We examine [...]” : I think here the authors provided too much detail which should be in the Results section.
Ln 61-63 : “We find that [...]” : This sentence should be in the Results section.
My main remark concerns the section 2.2. Indeed, in this section the authors explained how the fronts have been identified (supported by supplementary information in Appendix). I understand why the authors have organized their manuscript like this. However, they should add a sentence at the beginning of this part to clearly indicate that all the characteristics of these frontal structures are described in the Appendix. (I think it is difficult for the reader to well understand this part without read before the Appendix).
Furthermore, this section 2.2 is closely related to the section 2.5 named ‘regional context’ concerning the satellite products used in addition to the MVP data to identify these fronts. That is why, I suggest to move this section ‘regional context’ just after the section 2.2.
Ln 65 : Remove “California Current Ecosystem Long Term Ecological Research”. You have previously defined the acronym CCE-LTER in the Introduction (Ln 43).
Ln 67-68 : “[...] stations regularly spaced at high resolution” : Provide here the resolution.
Ln 119 : Add a reference to the section ‘regional context*’ after ‘SSH’. *section 2.5 in the manuscript or 2.3 in the revised manuscript (if you follow my previous suggestion).
Ln 130-134 : “The distribution of density [...]” : This sentence should be in the Results section.
Ln 135 : Do not start a new paragraph.
Ln 175 : Remove “Sea Surface Temperature” and “Sea Surface Height”. You have previously defined these acronyms.
Ln 182 : Add references after FSLE.
Ln 190 : Replace “then” with “secondly”.
Ln 195-196 : “In particular front C3 [...]” : I understand that you referred here to Fig. 5. But please indicate that for help the reader. It is also necessary for all this section (Ln 198-205).
Ln 207-221 : Here also please indicate at which figures you referred for help the reader.
Ln 231-233 : Please keep the same name (calanoids or copepods) in the text as in Fig. 6. (See also my comments about Fig. 6 in the Technical corrections).
Ln 236 : “wide physical fronts (such as E1 and F3)” and “narrow fronts (such as A and C2)”. Can you provide an order of magnitude to highlight why fronts E1 and F3 are wider than fronts A and C2 ?
This discussion contains rich information and the organization in scientific questions is very appreciable.
Ln 279 : “This dataset” refers to our dataset or the dataset used in the works that you cited previously ? Please clarify this sentence.
Ln 292 : Concerning the use of the SPASSO software during cruises, you can also add the followingreferences : Rousselet et al. (2018) (https://doi.org/10.5194/bg-15-2411-2018) and Barrillon et al. (2023) (https://doi.org/10.5194/bg-20-141-2023).
Ln 293 : Add references
Ln 317 : Add references
This part is a little short and can be improved (see my general comments).
Ln 28 : remove one “between”
Ln 44 : Write “Table 1” not “Tab. 1” (the word "Table" is never abbreviated and should be capitalized when followed by a number, following the Biogeosciences guidelines).
Ln 67 : Add parenthesis after “(Fig. 1”
Ln 78, 80, 84, 86 : Add a space between “100” and “m”.
Ln 92 : Add a space between “100” and “%”.
Ln 93 : Add a space before “The”.
Ln 129 : Add a space between “50” and “m”.
Ln 263 : Add a space between “100” and “m”.
Ln 268 : Write “Fig. 6” not “fig. 6”. See also Ln 271 and legend of figure 7. (Check I all the manuscript).
Ln 275 : Add a space between “10” and “m”.
Ln 277 : Add a space between “20” and “m”.
Ln 281 : Write in capitals “First”
In all the manuscript for Appendix figures do not write “sup. Fig Ax” or “Sup. Fig. Ax” just “Fig. Ax”.
In all the manuscript, units should be written exponentially (e.g. m s -1 not m/s) following the Biogeosciences guidelines. (See Ln 93, 105, 294 in the text and check also the units in the figures).
Please, consider changing the written of the coordinates in your maps, with a degree sign and a space when naming the direction (e.g. 36 ° N, 120 ° W), following the Biogeosciences guidelines.
Check the units on the legend of your figures. There are a lot of plots were units are missed.
There are some figures (for instance Fig. 3, 4, 5, A5, A11, A12, A13) where the typography is very small. I understand that sometime you have constraints for making figures, but where it is possible please increase the size of typography for help the reader.
Add “Latitude” and “Longitude” on the axis.
On the SST panel, the red crosses are not very visible on this colormap. Please, consider changing the color of the crosses.
On the Chl-a panel, the contrast of Chl-a is not very visible. Maybe, you can modify the color scale.
Correct the legend as : “Transect names (A, C2, C3, E1, E2, F1, F2, F3) ”
Legend : Define acronyms PRO as Prochlorococcus and SYN as Synechococcus.
Although calanoids is an order of copepods, please keep the same name in the figure and in the legend.
Nice figure !
Figures A1, A2, A3, A4
Add “Latitude” and “Longitude” on the axis.
Indicate in the legend that the black dots correspond to the CTD stations. In my opinion there are not all necessary and you can just keep the ones that indicate the transects with the frontal stations.
As for Fig. 1, the red crosses are not very visible on this colormap.
Add units of FSLE. Is it day -1 ?
Correct the legend as : “Prochlorococcus on the top row, Synechococcus on the bottom row [...]”.
HPLC (left column) and Flow Cytometry (right column).
Figures A11, A12, A13
Please consider if all these figures are really relevant (see my general comments). My suggestion is to choose only a few fronts that can be considered representative of all observed.
Furthermore on these figures, there are a lot of panels and the typography is minuscule. I suggest to present a limited number of variables.