Combined effects of low temperature and low light intensity on elemental content and macromolecules of coccolithophores

Shang, Jinlong; Ke, Wenting; Wang, Yinrui; Cai, Junqin; Chen, Yan; Liu, Xi; Han, Yonghe; Zhang, Hong; Xu, Kui; Zhang, Yong

doi:10.5194/egusphere-2025-5131

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https://doi.org/10.5194/egusphere-2025-5131

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18 Nov 2025

| 18 Nov 2025

Status: this preprint is open for discussion and under review for Biogeosciences (BG).

Combined effects of low temperature and low light intensity on elemental content and macromolecules of coccolithophores

Jinlong Shang, Wenting Ke, Yinrui Wang, Junqin Cai, Yan Chen, Xi Liu, Yonghe Han, Hong Zhang, Kui Xu, and Yong Zhang

Abstract. The calcifying coccolithophores Gephyrocapsa oceanica and Emiliania huxleyi can grow preferentially in deep waters (150–200 m), however, their physiological and biochemical strategies for acclimating to the combined constraints of low temperature and low irradiance remain unclear. In this study, we subjected three coccolithophore strains (G. oceanica NIES–1318, E. huxleyi PML B92/11 and RCC1266) to low temperature (9 °C) and low light intensity (15 μmol photons m^–2 s^–1), and compared their growth rates, particulate inorganic carbon (PIC), particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP) contents, as well as carbohydrate and lipid levels, with those under standard cultivation (21 °C, 150 μmol photons m^–2 s^–1). The results revealed that low temperature and low light intensity acted synergistically to decrease growth rate, POC contents and the POC : PON and POC : POP ratios, whereas did not significantly affect POP content in any of the strains. While increased light intensity enhanced PIC and PON contents at high temperature, it reduced them at low temperature. Low light intensity was identified as the primary factor leading to reduced carbohydrate and lipid level. Collectively, these findings indicate that to acclimate to low–temperature and low–light conditions, coccolithophores prioritized reducing the metabolic cost of carbohydrate and lipid biosynthesis, thereby allocating more resources to phosphorus metabolism–a physiological adjustment that can significantly influence biogeochemical cycles in the deep ocean.

Received: 16 Oct 2025 – Discussion started: 18 Nov 2025

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Jinlong Shang, Wenting Ke, Yinrui Wang, Junqin Cai, Yan Chen, Xi Liu, Yonghe Han, Hong Zhang, Kui Xu, and Yong Zhang

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'Comment on egusphere-2025-5131', Kunshan Gao, 23 Nov 2025 reply
The paper entitled “Combined effects of low temperature and low light intensity on elemental content and macromolecules of coccolithophores” by Shang et al. reports about the growth and elemental compositions of several coccolithorphore strains. It presents a potentially valuable dataset on the physiology of coccolithophores under conditions relevant to the bottom layer of euphotic zone in the oceans. The experimental approach is sound, and the core findings are clear. However, several key aspects require clarification and expansion to fully contextualize the results and strengthen the paper's conclusions before it can be considered for publication.
Major Comments
The results are generally straightforward and presented clearly. However, some data presentations, particularly in Figures [mention specific figures, e.g., 2 and 3], could be more concise. The current expressions, while detailed, are occasionally repetitive. Streamlining this would improve readability and impact. The values (%) should be mentioned without any digits after the decimal points.

The finding about the coccolithophores beyond 100 meters is intriguing. The authors should carefully consider and explicitly discuss the physiological state of these cells. It is highly plausible that the low light (near or lower than compensating light point) and temperature levels at these depths are insufficient to support sustained growth, and cells may merely be surviving in a dormant or maintenance state. The interpretation of the data should be nuanced to distinguish between active growth and simple persistence, which has significant ecological implications.

The discussion would be significantly strengthened by addressing the gaps between the laboratory conditions and the real-world environment at 100-150 meters. Specifically, please discuss how factors not replicated in your experiment—such as spectral light quality, pressure, nutrient pulses, and microbial interactions—might influence coccolithophore physiology in situ. Acknowledging these limitations will provide a more realistic framework for applying your findings to the natural ocean.

A critical point concerns temperature. The deep at 100-150 m to ocean is typically around 4°C, yet the culture experiments were conducted at 9°C. The authors must address this discrepancy. Based on the growth response shown in Figure 1, which indicates slower growth at lower temperatures, it is essential to extrapolate or model the expected growth rates and physiological responses at 4°C. Without this, the direct applicability of the results to the deep populations is uncertain. Please include a discussion on how the key findings (e.g., growth rate, calcification) would likely be different at the in-situtemperature of ~4°C.

When comparing "POC content differences across temperatures", the authors not only mention the core result that "POC content at 9°C is lower than at 21°C" (corresponding to Result 3.2) but also unnecessarily list detailed percentage data such as "a 28.78% reduction in POC for G. oceanica NIES–1318 under HTLL and a 38.53% reduction for E. huxleyi PML B92/11" (detailed data from Result 3.2). These detailed data have already been fully presented in the "Results" section via tables and text; the discussion only needs to discuss that "low temperature and low light significantly reduce POC content" without repeating specific values.

When describing "growth rate changes", the authors repeat strain-specific data such as "an 81.39% decrease in growth rate for G. oceanica under LTLL and a 63.18% decrease for E. huxleyi PML B92/11" (corresponding to Result 3.1). However, they do not subsequently analyze the reasons for "strain-specific differences in growth rates", making these data mere result restatements without adding new argumentative value.
Mechanistic Exploration:The discussion proposes the hypothesis that "stable POP content under low temperature and low light is due to phosphorus being preferentially allocated to nucleic acids and membrane phospholipids, with reduced investment in non-essential metabolic pathways" (corresponding to the result that POP shows no significant change in Result 3.2). However, it only cites Shemi et al. (2016)’s research on "membrane remodeling under phosphorus starvation" as indirect support, without providing direct data from this study on "changes in nucleic acid/membrane phospholipid content" (e.g., detecting RNA content or phospholipid composition via molecular biology methods). The weak connection between the hypothesis and the study’s own data reduces the persuasiveness of the mechanistic explanation.

- Ambiguous Mechanism for the Temperature-Dependent Reversal of Calcification
Regarding the counterintuitive result that "high light reduces PIC content at low temperatures", the discussion proposes two hypotheses: "photoinhibition disrupts ion transport" and "coccoliths act as microlenses for light concentration". However, it fails to clarify the primary-secondary relationship or synergistic effect between these two hypotheses:
If "ion balance disruption by photoinhibition" is the main cause, supplementary data on "changes in intracellular Ca²⁺/HCO₃⁻ concentrations under low temperature and high light" should be provided. Otherwise, such speculation should only be focused on low enzymatic activities related to photosynthesis and calcification, the latter demands energy from the former.

If the "microlens effect" is the main cause, an explanation is needed for "why the light-concentrating effect of coccoliths suddenly becomes prominent at low temperatures but not at high temperatures".

The simultaneous proposal of two hypotheses without targeted data support leads to a superficial mechanistic explanation.

Strain-Specific Differences: Inadequate Analysis of Causes and Lack of Universal Discussion
The study involves three coccolithophore strains (G. oceanica NIES–1318, E. huxleyi PML B92/11, RCC1266), and results show strain-specific variations in multiple indicators (e.g., the PIC:POC ratio only increases significantly for G. oceanica under LTLL, Result 3.3). However, the discussion only mentions at the end that "strain diversity helps coccolithophores adapt to different habitats" and does not further analyze the causes of these differences:
It fails to link the original habitat differences of the strains (e.g., NIES–1318 isolated from coastal waters of Japan, PML B92/11 from coastal waters of Norway) to explore whether "habitat adaptability causes differences in strain responses to low temperature and low light";

It does not explain strain specificity from a genetic background perspective (e.g., sequence differences in calcification-related genes or photosynthetic genes), resulting in "strain differences" being merely a descriptive feature of the results rather than a deep insight into "the diversity of coccolithophore adaptation strategies".

Extension of Ecological Significance: Insufficient Specific Linkage to Deep-Sea Biogeochemical Cycles
The discussion proposes that "the adaptation strategies of coccolithophores affect deep-sea biogeochemical cycles" but only generally mentions "enhanced carbon sequestration" and "underestimation of carbonate production", without establishing specific quantitative or process-based connections:
It does not combine the "changes in PIC:POC ratio" in this study (e.g., a 63.15% increase in PIC:POC for G. oceanica under LTLL) to assess the "potential increase in deep-sea carbon sinking rate ";

It does not explore the impact of "stable POP content" on deep-sea food chains (e.g., phosphorus is a limiting factor for deep-sea plankton; whether stable POP affects the feeding efficiency or trophic transfer of zooplankton), leading to ecological significance discussions remaining at a macro level without specific integration with deep-sea ecological processes.

Literature Comparison: When comparing with previous studies, the discussion has gaps in explaining "result differences":
Regarding the discrepancy that "this study finds decreased POC at 9°C, while previous studies reported unchanged or increased POC at 14°C/15°C", the authors only attribute it to "stronger inhibitory effects at 9°C" but ignore whether "light intensity conditions in previous studies (e.g., 60–480 μmol photons m⁻²s⁻¹ in Feng et al., 2008, vs. 15 μmol photons m⁻²s⁻¹ in this study) are also contributing factors", neglecting cross-study comparisons of "temperature-light interaction effects". Cellular quota of POC depends on C assimilation and cell division, so better to focus on POC production rate.

In summary, the manuscript addresses an interesting topic but requires revisions to fully realize its potential. The most critical issues are the interpretation of deep-water populations as "growing" versus "surviving," the discussion of experimental limitations relative to the deep ocean environment, and the crucial temperature extrapolation to 4°C. Addressing these points will greatly improve the manuscript's robustness and ecological relevance.

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Citation: https://doi.org/10.5194/egusphere-2025-5131-CC1

Jinlong Shang, Wenting Ke, Yinrui Wang, Junqin Cai, Yan Chen, Xi Liu, Yonghe Han, Hong Zhang, Kui Xu, and Yong Zhang

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https://doi.org/10.5194/egusphere-2025-5131-supplement

Jinlong Shang, Wenting Ke, Yinrui Wang, Junqin Cai, Yan Chen, Xi Liu, Yonghe Han, Hong Zhang, Kui Xu, and Yong Zhang

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Short summary

Here, we revealed that low temperature and low light intensity acted synergistically to decrease growth rates and particulate organic carbon contents, whereas did not significantly affect particulate organic phosphorus contents of three calcifying coccolithophores strains. These results are important for assessing the effect of phytoplankton on deep–sea biogeochemical cycles.


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