the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Mar 2026
Role of diatoms reproductive dynamics in plankton trophic webs
Abstract. Diatoms are key contributors to marine biogeochemical cycles, yet their distinctive reproductive strategies are rarely represented explicitly in ecosystem and biogeochemical models. In particular, the alternation between asexual size reduction and sexual size restitution introduces intrinsic size-structured dynamics that may influence plankton community structure and biodiversity. Here we incorporate a size-structured formulation of diatom reproductive dynamics into a coupled optical–biogeochemical plankton model to assess their impact on plankton biomass, diversity, and trophic interactions.
The model represents size-dependent asexual reproduction as a shrinking flux across diatom size classes and sexual reproduction as a restitution process activated below a critical size threshold. Using long-term simulations and a Monte Carlo ensemble exploring uncertainty in reproductive parameters, we evaluate the sensitivity of plankton communities to variations in reproduction rates.
Results show that asexual reproduction exerts a dominant control on diatom biomass and size structure, producing nonlinear, threshold-like responses capable of reorganizing phytoplankton functional composition and propagate upward through the food web. Sexual reproduction acts mainly as a secondary modulator, while trophic interactions buffer variability at higher trophic levels. These findings highlight reproductive dynamics as important regulators of plankton biodiversity and biogeochemical functioning.
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Status: open (until 07 Jun 2026)
- RC1: 'Comment on egusphere-2026-1437', Anonymous Referee #1, 20 May 2026 reply
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RC2: 'Comment on egusphere-2026-1437', Anonymous Referee #2, 21 May 2026
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General feedback
The manuscript egusphere-2026-1437 “Role of diatoms reproductive dynamics in plankton trophic webs” discusses the cascading effects of cell size dynamics of diatoms, in relation to asexual and sexual reproduction, on the planktonic foodweb. The results presented here could benefit ecosystem and biogechemical models, especially in the context of trait-based modeling, that often disregard such processes.
The authors performed simulations of a size-based model of diatoms with a planktonic food web encompassing cyanobacteria up to carnivorous mesozooplankton.
While the research question appeared to be clearly conveyed, the manuscript would benefit from clarifications with regards to the methods. The results are sometimes difficult to understand, especially the cascading effects on the food web, as the interactions between trophic levels are not clearly described.
This report is composed of three sections: (1) major comments, (2) minor comments, and (3) optional suggestions.
1 – Major comments
The model description would benefit from more explanations. I found the theoretical background sometimes difficult to understand.
a) Line 91: functional diversity biogeochemical model – the calculation of the growth rate and mortality rate were difficult to understand.
If I understand well, grazing pressure is a function of the prey size selectivity of predators (Lines 151-152), however the relation between the polynomial delta(s) (after Eq. 4) and the size-dependent predation risk was unclear?
b) Eq. (6) gives the boundary condition for the maximum size of diatoms. The text would benefit from a clearer description of the equation.
The relation between Eq. (6) and lines 127-128 was not clear to me.
Line 127: what is b(s) referencing to? I could not find it anywhere else in the text.
c) Section 2.3.: “Predation interactions are parametrized through allometric relations” (Line 151).
It is unclear which process is defined by an allometry. Is it the predation risk of diatoms, the prey preference of predators, or the ingestion rate?
If the prey size preference follows an allometry of the predator’s body size, the authors might want to discuss this assumption in the text. Some herbivorous plankton, such as dinoflagellates https://doi.org/10.1007/s00227-022-04102-2, can show an optimal prey size that is independent of their body size.
d) The manuscript is discussing the cascading effects of size dynamics of diatoms, related to sexual reproduction, on the food web.
It would be helpful to have a table or figure showing the trophic relationships between trophic levels, such as the prey preferences of grazers and predators. The lack of description of the trophic linkages makes it difficult to understand the results.
e) Section 2.3.1 – It is unclear how the optical trait is related to diatoms size. The text would benefit from a description of the size – optical trait relationships in the model.
f) Line 258: “… indicating a competitive displacement as dinoflagellates become increasingly dominant under enhanced asexual reproduction …” Could the authors explain why? Are the dinoflagellates feeding on small diatoms?
g) Are the dinoflagellates autotrophs or mixo/heterotrophs? From the text, it is unclear if dinoflagellates are strictly autotrophs or mixotrophs. The authors might want to specify it.
h) Line 260-263: “Smaller phytoplankton groups … show limited sensitivity to the asexual reproduction perturbation … suggesting that their dynamics are primarily controlled by processes other than direct reproduction rate modulation in this parameter regime …”
This paragraph refers to phytoplankton other than diatoms. However, in this sentence, it seems that the asexual reproduction rate perturbation is applied to all phytoplankton groups. Is it true?
2 – Minor comments
a) Line 241-244: Panels g and j show strong transition zones. Interestingly, panels h and i show a similar pattern as in d-f. Do the authors have an idea why?
b) Line 275-279: It might be useful to also plot the contribution of large sizes.
c) Spelling mistakes
Line 17: “… drinkable water, and a clean and sustainable ...”
Line 31: “… especially in multicellular zooplankton ...”
Line 43: “... whole diatom community as small cells becomes more abundant ...” It is not clear what this becomes is.
Line 44: “… the original size, a common strategy is sexual reproduction ...”
Line 47: “… showed that newborn cells shrinking below their sexualization
size threshold (SST) acquire sexual competence ...”
Line 78-79: The sentence “In the asexual part of the reproduction cycle one of the two daughter cells is smaller than the other by two times the frustule width” was unclear to me. Could the authors reformulate?
Line 123: “… conditions are required. At t0 the distribution ...”
Line 133: “… newly generated … composed of clones, evolve ...”
Line 138-139: “… abiotic regulations of growth predation …” This sentence is unclear, could the authors reformulate? Maybe some commas are missing.
Line 141: “… and in particular in term of cohorts time scale evolution as shown in Fig.1” Do the authors mean the evolution timescale of cohorts?
Line 146: “… on the BFM98 model (Álvarez et al. 2025).”
Line 151: “Predation interactions …”
Line 196: “… ni (t) represents the concentration ...”
Line 206: “… of 50 µm …”
Line 222: “phasing” Do the authors mean “dynamics”?
Line 229: “… reproduction rates with constant multiplicative factors …”
Line 256: “… perturbations below unity …” Do the authors mean below 1? Please also check Line 269. The word “unity” is unclear.
Line 269: This sentence is unclear. Could the authors reformulate?
Line 302: “… coherently with previous results …” Do the authors mean “in accordance with” or “in coherence with” previous results?
Line 317: “… pathways, damping high-frequency …” Do the authors mean “dampening”?
Line 333: “… changes in the Shannon index reflect …”
Line 375: The sentence is unclear. Could the authors reformulate?
Line 389: “… depends on ...”
3 – Suggestions
Please find below a list of suggestions aimed at improving the text and figures. Elements in this section are optional for the review of the manuscript, but I think it would improve the overall clarity of the text.
a) In Fig. 2: What is the reason behind choosing the numbers for the trophic levels? They do not correspond to the ESD or the size classes described below, which makes it more difficult to compare the figure and the caption.
b) Fig. 4: The authors might want to increase the fontsize of the figure, if possible.
Citation: https://doi.org/10.5194/egusphere-2026-1437-RC2
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- 1
The manuscript reports the extension of an existing biogeochemical plankton model with diatoms. The novelty compared to similar models is an explicit representation of the special diatom life history with sexual reproduction after a number of cell divisions. The manuscript has three parts: first a theoretical analysis of the diatom size trajectories between sexual reproduction events, a description of the new diatom module in the existing biogeochemical model, and finally analysis of the results, including comparison with data and sensitivity of parameters.
The problem of diatom sexual reproduction is interesting and the impacts of ignoring this life history in traditional biogeochemical models deserves to be investigated. However, I struggled reviewing the manuscript because the central methodological description lacked a concise description of central assumptions and parameters. I was therefore unable to properly review the results and discussion sections of the manuscript, and assess the validity of the results.
Major comments:
1. Central elements of the methodology are missing or are unclear (section 2.3):
a) how does the ratio between the size of new sexually reproduced cells (large) and the size of sexual reproduction (small) enter into the model? It seems as if all cells become smaller, regardless of their species, until they reach a lower limit (50 um), where there is a flux from the smallest size class towards the largest one. That rate of sexual reproduction is only described loosely as being proportional to NPP. Further, if that is correctly understood, then the diatom model essentially models a fictive species that has a ratio between new cells and sexually reproducing cell of a factor 10 (the size range of diatom cells) which is much larger than the ratio in individual species (50/20). If that is correctly understood, then the sexual reproduction model does not faithfully represent the sexual reproduction dynamics of the diatoms. The implication of this approximation should be discussed.
b) How is the growth rate rho (or is it a division rate?) modeled? I miss a description of the physiological model of the diatoms: which resources do the use? What are the affinities (and how do they scale with size)? What is the maximum growth rate (a unimodal size dependency is alluded to, but it should be shown). Are there any density-dependent terms? Here I miss equations for the full diatom model and figures that show the data that the size-based relations have been fitted to.
c) How is the central equation (9) derived? I miss a description of all the parameters and relations that enter into this relationship.
d) It would be great to see an analysis of the diatom model in isolation and in an idealized setting. E.g. solving for the size distribution under a specific light and nutrient environment. How does the distribution look?
e) Lastly, I miss a better description of the “mother-model”. It is described as a “optical” model, however, the optical-related traits play no role in the present manuscript. Specifically, I miss a description of the main principles and the main governing equations, with a full set of equations and parameters in the appendix (parameters and equations for the new diatom model could go in the main text).
2. The theoretical analysis (section 2.2) feel very disjoint from the rest of the manuscript. It uses the methods of characteristics to calculate the size trajectories of diatoms (fig 1). However, this is done with an idealized division rate, which is different from the emergent division rates in the rest of the paper. Further, these trajectories could have been calculated without entering into the entire discussion of characteristics by just integrating (4) directly; the abundances (3) are never used. Finally, the central result does not appear to be used in the rest of the manuscript (perhaps it is, but then I did not find it). As it is, the manuscript would be sharper without this section.
3) The model contains a sensitivity analysis, which is nice. However, I miss a comparison of the new model with sexual reproduction to the original model without sexual reproduction. Essentially addressing the questions: how important is it to add sexual reproduction to resolve community dynamics.
Minor comments:
Line 12. “…secondary modulator”. Please be more specific
Line 16. Is biodiversity a “mechanism”? would it be better to describe as a “property”?
Line 18. Perhaps better to remove “coarse” because FR type of representations can actually be quite complex.
Line 29 and 33: “e.g.” instead of “i.e.”
Line 43. “… as abundance increases”.
Line 52-58. This paragraph feels a bit out of place here. It might work better before the previous paragraph.
Line 53. I would add “affinitiy to light and nutrient uptakes” as other properties that are influenced by cell size.
Line 75: 50-20% in mass or diameter?
Line 76: What does “this” refer to in “…departing from this theoretical…”?
Line 77. “mechanisms are “ => “as”
Line 79-83. Why is this information relevant here?
Line 87. Remove “with a method”
Line 95. Is S really defined all the way down to a size zero?
Eq 1 (and elsewhere): The differential “d” is an operator and should not be in italics.
Line 115 (and elsewhere): Units should not be in italics.
Section 2.3.1: The optical traits appears to be of secondary importance to this manuscript. Perhaps just move to a supplementary.
Line 211. Is there a reference that describes the site?
Fig 4. All panels should have the same colour scale so it is easy to see which parameters matters compared to the others. Font size on axes should be increased.