the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jan 2026
Temperature and light regulated patterns of physiology, morphology and elemental stoichiometry in geographically distinct isolates of a cosmopolitan diatom
Abstract. Anthropogenic influence on climate change has profound and diverse consequences on marine ecosystems. At the base of the food web, phytoplankton, are experiencing altered temperature regimes. In south-east Australia, the southward extension of warm waters, driven in part by the East Australian Current (EAC), is rapidly warming regional ocean temperatures, leading to the intensification of marine heat waves (MHWs). In this study, we investigated thermally adapted Leptocylindrus danicus strains isolated from four distinct latitudes to determine how silica production rates vary with temperature and irradiance. We also explored how the intra-specific phenotypic variability affects physiology and silica production. We found strong latitudinal effects on strain-specific cell volume (ranging from 313 ± 22 µm2 to 2070 ± 105 µm3) and pigment quotas (chl a 1.04 ± 0.21 to 3.70 ± 1.17 pg cell-1; chl c 0.26 ± 0.07 to 2.09 ± 1.50 pg cell-1), both increasing with increasing temperature. There was also a significant effect of temperature on silicification rates, which varied depending on growth irradiance and cell normalisation. By identifying temperature and light regulated shifts in growth, morphology and silicification in a cosmopolitan diatom, we can gain an improved understanding of the range in intraspecific phenotypic variability of this key phytoplankton group. This study provides an assessment on how key diatom traits vary along a latitudinal gradient, providing unique insight into how ocean warming may influence resilience and adaptation potential of L. danicus, and how shift in physiology may impact diatom-regulated carbon and silicon cycling.
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Status: open (until 13 Mar 2026)
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RC1: 'Comment on egusphere-2026-45', Anonymous Referee #1, 27 Jan 2026
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AC1: 'Reply on RC1', Katherina Petrou, 03 Feb 2026
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The authors thank the reviewer for taking time to review our paper and provide the thoughtful comments and recommendations for discussion of our study. Thank you also for the reference to the paper by Kuefner et al. it is very interesting and nicely supports the important role of temperature on diatom silicification.
Microalgal acclimation is indeed short lived, the result of a few generations – covering several weeks. The authors are somewhat curious to know in what way the reviewer believes that including the temperature over a month would influence our interpretation? Does the reviewer have a hypothesis on this point? We have temperature data for each site over the spring period, and will add a range (SD) to the table as we agree this is more informative. We are grateful for the suggestion.
The authors agree with the reviewer that nutrients would also play an important role in physiology in situ, however, in Spring nutrients are often not limiting, hence diatom blooms off the coast of NSW occur typically in spring. Furthermore, the exclusion of nutrient manipulations was also a logistic one, to better control for the effect of temperature, considered the most significant driver (as was the case in Kuefner et al 2020). As our principal aim was to use latitudinally distinct strains to assess how temperature may influence silica production. That said, the authors like the idea of adding in situ nutrient data to provide a more detailed picture of the in situ Spring conditions.
I’m not sure the authors based our hypothesis on the increase temperature resulting in shorter generation time, impacting silicification and cell biovolume, rather we were following what our data showed. This interpretation is an attempt to explain the data, which we believe has merit and is grounded in literature and logic. While we openly acknowledge that other factors may influence cell characteristics and physiology, the interpretation needs to be limited to what was tested and manipulated, rather than extrapolate too broadly. That said, we agree with the point about the inclusion of discussion around nutrients and other potential influences and the need to test these with temperature and light.
The authors are grateful for this initial discussion around our study and will incorporate these key points into the revised version of the manuscript to deepen the discourse around the findings and the potential impacts.
Citation: https://doi.org/10.5194/egusphere-2026-45-AC1 -
RC2: 'Reply on AC1', Anonymous Referee #1, 03 Feb 2026
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Thank you very much for your answers to my comments.
Concerning your question : generally, the environmental conditions characterizing the ecological niche of diatoms are measured during the month preceding sampling (see, for example, Carayon et al., 2019), as the lifespan, and therefore the acclimatization period of taxa is short. I would therefore have appreciated more precise information on environmental conditions, in order to be sure that the strains collected corresponded to the expected categories.
Citation: https://doi.org/10.5194/egusphere-2026-45-RC2
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RC2: 'Reply on AC1', Anonymous Referee #1, 03 Feb 2026
reply
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AC1: 'Reply on RC1', Katherina Petrou, 03 Feb 2026
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The paper aims to identify temperature regulated patterns in silicification in multiple strains of the planctonic diatom L. danicus. By looking at strains with locally adapted thermal niches from South-East Australia, the authors aim to provide new insights into how ocean warming may influence a species’growth and how diatom phenotypic plasticity provides resilience to rapid environmental change.
General aspects in a few words :
The paper deals with interactions between biological, chemical, and physical processes in coastal environments and is thus completely within the scope of BG.
The concepts handled are not particularly new but data was specifically acquired for the paper.
Conclusions are contrasted and hardly generalizable to diatom communities as a whole.
In my opinion, the experimental design, which only considers temperature and light, should also take nutrients into account. I elaborate on this aspect in the text below.
Yes, experiments are particularly well described.
Yes
Yes
Yes
Yes, the paper si particularly well written. All the details necessary for a good understanding of the text and the objectives of the study are provided in fluent language. I have no comments regarding the form.
Yes
Yes
Yes
Specific comments :
The article is very well written. The introduction sets out the context and objectives very clearly. The methodology is well described. I therefore have no comments on the structure or presentation of the manuscript, which is of very high quality.
However, I would like to raise two methodological points that I think are important to consider. I am aware that the authors cannot generate the additional data requested at this stage, but they could at least address the limitations of their experimental design in the discussion, in order to adjust their conclusions accordingly.
1) The interpretation of the results is based on the assumption that clones are adapted to contrasting temperature conditions in situ, and annual averages for the sampling sites are provided. However, diatoms are microalgae that reproduce very rapidly, so in general the environmental conditions describing the sampling site cover a period of one month (three weeks before sampling and one week after). Do the authors have temperature records for this time period at the sampling sites? If so, it would be important to include them as they may impact the interpretation of the results. It would also be important to have in situ nutrient measurements (N, P), as these greatly affect diatom growth and physiological status.
2) The article's hypothesis is based on the fact that the higher the temperature, the greater the productivity. The increase in temperature thus implies a shorter generation time and impacts silicification and cell biovolume. However, there are many other environmental drivers that can affect these charactristics, including bioavailability of nitrogen, phosphorus, and iron. Increased nutrients also act by increasing generation time (see for example Kuefner et al., 2020). The article focuses only on the influence of temperature on the potential of planktonic diatoms to adapt to climate change. However, climate change also induces changes in the availability of macronutrients. The introduction suggests that “warmer surface waters can cause a shallowing of the surface mixed layer, forming a barrier to vertical exchange of nutrients from depth and constraining phytoplankton in the upper surface waters, exposing them to high irradiances and reduced nutrient availability.” I therefore believe that it would have been important not only to measure nutrients at the sampling sites, but also to introduce the “nutrients” variable into the experimental design. The study would have benefited from combining temperature, irradiance, and nutrients in the experimental design. The study site and biological model chosen would therefore have been particularly interesting for advancing our knowledge of how planktonic species adapt to rising temperatures combined with low nitrogen and phosphorus availability. Although it is too late to add this variable, I believe it is important for the authors to enrich their discussion with this aspect.
I think the discussion could be strengthened by these two points. The discussion at this stage does not appear to be sufficiently in-depth. The first paragraph of this section is, moreover, a repetition of the introduction; it would be more interesting to summarize the results obtained.
Kuefner, W., Ossyssek, S., Geist, J., & Raeder, U. (2020). The silicification value: a novel diatom-based indicator to assess climate change in freshwater habitats. Diatom research, 35(1), 1-16.