Benthic foraminiferal species tolerance for hydrothermal activity: a case of study from the Lucky Strike vent field

Dessandier, Pierre-Antoine; Panieri, Giuliana; Leroux, Riwan; Pelleter, Ewan; Fuchs, Sandra; Bouriat, Alizé; Boissier, Audrey; Cheron, Sandrine; Sarrazin, Jozée

doi:10.5194/egusphere-2026-133

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https://doi.org/10.5194/egusphere-2026-133

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23 Jan 2026

| 23 Jan 2026

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

Benthic foraminiferal species tolerance for hydrothermal activity: a case of study from the Lucky Strike vent field

Pierre-Antoine Dessandier, Giuliana Panieri, Riwan Leroux, Ewan Pelleter, Sandra Fuchs, Alizé Bouriat, Audrey Boissier, Sandrine Cheron, and Jozée Sarrazin

Abstract. Hydrothermal vent fields represent dynamic environments hosting rich ecosystems. At the Mid-Atlantic Ridge, the Lucky Strike (LS) vent field has been the focus of multiple biological studies. While ecological studies have been focusing on microbial and macrofaunal communities, some groups still remained out of the scope. We present here the first ecological study of benthic foraminifera inhabiting soft sediments in the peripheries of hydrothermal edifices at LS. A total of fifteen blade cores were analyzed. We combine microhabitat environmental descriptors with faunal density and diversity of benthic foraminifera (living & fossil) to investigate the impact of hydrothermal activity on their ecology. The far periphery, ~150 m away from vents, harbors a community of diverse foraminifera feeding on pre-degraded organic matter characterized by a phytoplankton detrital signal. Communities located at intermediate distance (~ 50 m) from venting showed the presence of opportunistic species likely feeding on chemosynthetic microorganisms. Finally, environments closer to active sites (few meters) showed very low abundance of living individuals, as the presence of harsh environmental conditions may limit foraminiferal growth. Unexpectedly, the presence of widespread iron-oxidizer bacterial biofilms was associated to the dissolution of all biogenic carbonate content raising questions on their impact on regional carbon budget.

Received: 13 Jan 2026 – Discussion started: 23 Jan 2026

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Pierre-Antoine Dessandier, Giuliana Panieri, Riwan Leroux, Ewan Pelleter, Sandra Fuchs, Alizé Bouriat, Audrey Boissier, Sandrine Cheron, and Jozée Sarrazin

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RC1:
'Comment on egusphere-2026-133', Anonymous Referee #1, 14 Apr 2026 reply
Does the paper address relevant scientific questions within the scope of BG? Yes

Does the paper present novel concepts, ideas, tools, or data? New foram data acquired with traditional morphological approach, not well suited in these deep sea environments where a big part of the community has soft-shells

Are substantial conclusions reached? Mainly based on comparisons with other foram assemblages

Are the scientific methods and assumptions valid and clearly outlined? The protocols used do not allow to view the total foram community. There is a lack of direct evidence for the trophic role of forams.

Are the results sufficient to support the interpretations and conclusions? In many cases, no. For example, the trophic network would need more investigations and the absence of forams in certain environments may be due to the protocol used (more precise examples in the detailed comments).

Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? The authors need to say if they picked wet or dry to collect forams.

Do the authors give proper credit to related work and clearly indicate their own new/original contribution? In the intro, there is a need for more refs from other authors and older than the work of the first author for forams. More refs are also needed in the discussion on foram trophic strategies, extreme environments in general and with low pH.

Does the title clearly reflect the contents of the paper? The paper is more about the communities of forams found in different environments around hydrothermal vents than on their tolerance to ecological parameters

Does the abstract provide a concise and complete summary? Yes

Is the overall presentation well structured and clear? Yes

Is the language fluent and precise? Not always, see detailed comments.

Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? The authors need to check the scientific names of forams through the manuscript and supplementary files as there are many typos in addition to some taxonomic discussions raised in detailed comments.

Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Exposed below in detailed comments.

Are the number and quality of references appropriate? More refs are needed in the intro and discussion.

Is the amount and quality of supplementary material appropriate? Plates 1a and 1b: some scientific names with typos, some sides not ideal for taxonomic identification

General comments:
This is a good point to finally have a study of foraminifera from these environments. The environmental data are well presented and there are some interesting points raised. However, this study does not take in account the complete community of benthic foraminifera as it is only focusing on hard shelled forams. This is problematic as it is known that a substantial part of the foram community is represented by soft-shelled forams in the deep sea (see work of Andy Gooday on morphology and Jan Pawlowski’s group on eDNA).
The vision of the trophic network is a bit simplistic and too theoretical; there is a lack of field proofs directly acquired from the forams (e.g. labeled isotopes, TEM images or microbiome analyses) as only environmental analyses are presented here and connected to foram assemblages without strong or direct evidence.
Detailed comments:
l. 20-21:”feeding on pre-degraded OM characterised by phytoplankton detrital signal” → based on which data?
l. 24-25: only data for hard-shelled forams, what about soft-shelled ones?
l. 28: field instead of filed
l. 34: “benthic organisms” is vague, you mean macro-organisms, metazoa?? Forams can also feed on larger organisms, e.g. nematods (Dupuy et al. 2010) or scavenge on dead animals (Nomaki et al. 2025).
l. 36-37: at least since the 1960s!
l. 43: there is an important body of references predating this one!
l. 45: there are very different kings of extreme environments (e.g. anoxic, deep sea, temperature, salinity,…), here you focus only on cold seeps or hydrothermal vents, right?
l. 47: expand the number of citations if possible
l. 48: here again, you refer to a certain type of extreme environment, not all of them
l. 75-78: you need to say that only hard-shelled forams were studied here
l. 98: what do you mean with “local biology”, biodiversity? Metabolic activity?
l. 125: Rose Bengal in English
l. 125-126: this protocol is only well suited for hard-shelled forams, ethanol does not preserve well soft-shelled forams. Did you do wet or dry picking? Could you tell it in the manuscript?
l. 128: Loeblich and Tappan 1987 instead of 1988 (a lot of discussions about that, e.g. ww.cambridge.org/core/journals/journal-of-paleontology/article/abs/publication-date-of-foraminiferal-genera-and-their-classification/FEC5AADF8ED5E8160F4674202DB514F5)
l. 159-163: to include dead forams can give long term tendencies, but does not replace the missing data of soft-shelled forams
l. 164-165: you need to update your taxonomy here, C. wuellerstorfi and C. pachyderma were moved to another genus a long time ago (Cibicidoides, Schweizer et al. 2009) and there are new discussions on placing wuellerstorif in Lobatula (WoRMS), there are also discussions about Epistominella in WoRMS
l. 177: can you really speak about microhabitat characterisation when you do bulk analyses?
Fig. 3: could you analyse all the samples that you examined for forams? If yes, say it in the caption as it is not clear which samples you show here
l. 201-211: are these sedimentation rates typical for this kind of environment? The deep sea?
l. 230-231: did you collect more than 300 individuals per sample? Or 300 for live and 300 for dead forams? Could you clarify this sentence?
l. 232: are the species evenly distributed or are there some dominant ones?
l. 236-237: you only used the counts of live forams here?
l. 257-259: this sentence is difficult to understand, a bit out of context
l. 270: Miliolida order
Fig. 5: it could be interesting to distinguish the different orders with specific colour codes
l. 292: 44% is not very high, is it statistically strong enough?
l. 316: did you check for the presence of benthic squatters in the planktonic foram shells? (e.g. https://www.researchgate.net/publication/315797952_Benthic_foraminiferal_squatters_species_that_inhabit_the_tests_of_other_foraminifera)
l. 321-323: foraminiferal potential food source as there was no direct measurement from the forams themselves
l. 329-330: this sentence is unclear, develop how it is a key
l. 348-350: it was shown in other environments with low pH (Baltic Sea, Charrieau et al. 2018 or mudflat with cable bacteria, Daviray et al. 2024) that rotaliids can survive in low pH environments, even with a dissolved shell; therefore other approaches could be useful here to check that no foram can live on these mats (e.g. formalin fixed samples to preserve soft-shelled, dissolved or naked forams or eDNA/eRNA to get total foram diversity)
l. 368-370: do you have refs for this suggestion? The presence of both foram groups and food source is not enough to suggest
l. 370-376: interesting hypothesis
l. 379-382: I agree with the difference of geochemistry, but how the sampling strategy of both studies could explain this difference?
l. 382-384: this is not a criterion to distinguish species as C. wuellerstorfi are also attached to their substrate; moreover, you could potentially have other species of cibicidids here
l. 384-386: Lobatula lobatula (formerly C. lobatulus) is a true genetic species found in shallow water and is well separated from these deep sea specimens, even if some look morphologically similar.
l. 391: there are older refs with in situ observations (the cited paper deals with specimens in aquaria)
l. 397: agglutinated instead of non-calcareous (as only hard-shelled forams were examined here)
l. 397-398: Vanhoeffenella instead of Vanhoeffela and Martinottiella instead of Martinorinella
l. 399-400: there is a huge variety of monothalamids, not only sessile species, but also vagile ones, soft-shelled ones, naked ones of all sizes. With the methodology used here, it is impossible to get track of all of them. Therefore you need to specify which kind of monothalamids you mean here.
l. 401-402: their occurrence there is mainly limited because of the sampling protocol, it is then impossible to say that they are absent in Lucky Strike
l. 402-404: do you have other refs showing narrower ecological preferences in agglutinated forams compared to calcitic ones?
l. 405: which species? Belonging to which groups? Be more precise here
l. 407-408: is it due to lower densities of biocoenoses or to lower preservation conditions after death?
l. 412: fresher OM deduced from what? Foram community or direct measurement?
l. 413: was the higher microbial productivity measured?
l. 416-419: this is true for opportunistic species, but it is not the case for all deep sea species
l. 423-426: seasonal sampling would be needed to check that assumption
l. 426-428: is it also the case in your samples?
l. 432: could you say which living community?
l. 434-436: could this change observed between live and dead assemblages be due to environmental changes (vent activity, current,…)?
l. 439-441: live Fissurina?
l. 447-448: absolutely, therefore it is difficult to make hypotheses out of dead assemblages here
l. 456-457: as explained in the introduction, the bypass is more due to a lack of study of the meiofauna and could not give a full picture of the trophic network in these environments
l. 466-468: the demonstration is rather indirect and needs more direct evidence
l. 469: what is the evidence of this adaptation?
l. 472: organic-walled specimens could not be targeted by this study with the protocol used
l. 482: foraminifera cannot be a trophic chain by themselves, only an element of the chain
l. 484: hydrothermal chimneys inhabited by microbial communities?
l. 487-488: you need to develop this sentence to link both before and after sentences
Supp. Files:
Corrections to make in the figure caption:
1A: 10) Fissurina, 13) Fissurina, 28) other side more interesting for identification, 32) same
1B. 8) is not Pyrgo, 9) Fissurina, 11) Fissurina, 25) other side more interesting for identification, 28) looks more like Planulina ariminensis than C. wuellerstorfi, 31) Vanhoeffenella

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Citation: https://doi.org/10.5194/egusphere-2026-133-RC1
RC2: 'Comment on egusphere-2026-133', Anonymous Referee #2, 22 Apr 2026 reply

Dear Editor,

the paper entitled "Benthic foraminiferal species tolerance for hydrothermal activity: a case of study from the Lucky Strike vent field" by Pierre-Antoine Dessandier and co-authors from IFREMER and Geo-Ocean Brest, and from the University of Tromsö describes, for the first time, first ecological benthic foraminiferal faunas and dead assemblages from the immediate vicinity hydrothermal vents on the Mid-Atlantic Ridge. They comprise the familiar bathyal faunas at distances beyond 150 m, faunas characterized by opportunistic species feeding on chemosynthetic bacteria closer to the vents, and almost no foraminifera in brown sands covered by iron-oxidizer bacterial biofilms prevailing at distances of a few meters to the chimneys. The data and observations presented in this study are of great value for the recognition and interpretation of foraminiferal zonations at distance to cold seeps and saline springs in both, terrestrial and marine environments. The subject is timely, innovative, and I therefore recommend publication with a few, mainly technical emendations .

Line 34: " benthic organisms as predators and microorganisms" rather should read "benthic macro- and meiofauna mainly as predators and bacteria".
Line 35: "These organisms" rather should read "Benthic foraminifera".
Line 39, 40: The focus on microbes and macrofauna did not impede micropaleontologists to pursue such studies, in fact the sampling requires ROVs or submersibles, which are not available for everybody.
Lines 42, 43, and 47: please provide more and appropriate citations to support your case, also considering elder and most recent publications.
Line 44: "material" should be omitted, otherwise the sentence is difficult to understand.
Line 48: replace "thus" by "may".
Line 50: please provide a reference here.
Line 52: does this statement only applies to mid-oceanic ridges or is it valid for any volcanic province?
Line 57: "endemic" should be omitted.
Line 61: please provide the oxygenation state of Fe.
Line 64: they may stand far higher temperatures, please have a look at Noémie Deldicq's work.
Lines 71, 72: " the foraminiferal compartment" should simply read "benthic foraminifera".
Lines 88, 89: " by hydrothermal slab corresponding to breccia" should simply read "by a hydrothermal breccia".
Line 93: Figure 1 is impossible to read and lacks details.. Please provide a simple, contoured bathymetric map, the main spreading axis indicated by a thick, stippled line, a shaded area for the lava lake mentioned in the text, bold dots in black or red for the stations, bold, black and larger station numbers and chimney names.
Line 100 ff: it is mandatory to either present a species name with author and year when it is mentioned only once, or, to provide a species list with all taxa mentioned in the paper as Appendix 1, complying with the ICZN. It is also mandatory that the citations of the original species descriptions are included in the reference list.
Lines 118, 119: when the deployment of a push corer does not yield sedimentary material inside the polyacryl tube, then it is not a core, not worth mentioning.
Line 125: "Bengale" should read "Bengal".
Lines 126-128: do you mean that you have determined the benthic foraminiferal species by using the Atlas of Benthic Foraminifera (Holbourn et al., 2013), and their generic affiliation mainly follows Loeblich and Tappan (1988)? Ann Holbourn's work comprises many extinct species and does not cover the whole variety of deep-sea species. You certainly also have used Gwynn Jones book on the Challenger Foraminifera, Frances parker's papers on Gulf of Mexico foraminifera and probably also the web-based WORMS, didn't you?
Line 126: please provide more details on foraminiferal sample treatment, in particular staining time, mesh size used for washing the samples, tap water or sea water used for washing the samples, later fractionation, splitting, device, etc. etc.
Line 129: I found it a pity that Plates 1 and 2 are given in the supplement. Couldn't they be included in the paper?
Line 133: please provide a key to the abbreviations used in the Table header, please also spell out the geographical coordinates, e.g. 37° 17.296'N and not 37 17.296.
Line 137: they were first thawed again and dried, right?
Line 155: grain size measurements were not mentioned before. please provide details.
Line 164: even if you disagree, and you may have sound reasons for that, I strongly recommend to use the genus and species denominations provided by WORMS. Your personal opinion could be documented by e.g. "Cibicides lobatulus (Lobatula lobatula of authors)"
Line 159: One never must do this, never ever. There is an old paper by John Murray explaining why. You can not ameliorate the diversity of the living fauna you have observed in a given sample volume by an aliquot of the dead assemblage that has been formed in thousands of years. Living fauna and dead assemblage have to be analysed separately. Strictly.
Line 165: pooling species of the same genus but with different ecological preferences is not straightforward.
Lines 228-235: please only discuss the dead assemblage here.
Line 265, Table 3: please also provide the p-values in a separate column.
Line 301: it would be appropriate to insert a short subchapter summarizing the visual observations made while sampling and linking them to sedimentary properties. Doing so, the following chapters were much better comprehensible.
Line 309: please refer to the core numbers and age models, otherwise the reader is confused.
Line 313: has this been described before? I do not remember.
Line 317: is it now organic carbon?
Line 318: please refer to a data table.
Line 330: if this is the case, please quote the d13C values measured on dried bacteria from these microbial mats., and link them to the respective values from foraminiferal tests.
Line 349: what a pH has ben measured on-site in these mats by Victor 6000?
Line 350: you are probably aware that arenaceous foraminifera inhabit salt marsh soils with pH values of 6.18? Why should arenaceous deep sea foraminifera should not be able to live in such acidic environments? have you observed some, at least in the dead assemblage?
Line 370: do you mean the last spring bloom?
Line 381: convincing, I agree.
Line 391: this is an experimental study. Please also refer to foraminiferal distribution studies.
Line 392: it is rather due to their microhabitat preference and flux of organic matter. Please check Altenbach et al., 1999, Journal of Foraminiferal Research 29, 173–185, there Figure 2
Line 441: the genus Fissurina comprises 480 different species according to WORMS. The can not all have the same ecological requirements, hence it is not justified to provide general statements on the behaviour of this genus.
Line 444: exactly, see above.
Line 461: there are only a very few papers documenting that predators are seeking out for foraminifera as prey. Mostly, they become ingested accidentally by sediment dwellers, and they survive the passage through the digestive system. With reference to the ability of foraminifera to consume a large volume of food in a short period, and do not provide it to a higher trophic level, they are rather considered as a dead-end street in the food web.
Line 472: has this been said before?
Line 281 ff: the last paragraph of the Conclusions is quite speculative, hardly based on data produced by this study, and may be omitted. Deep-sea mining is not in sight.
Supplements: to my view, only Supplement 2 and 6 deserve to be provided separately. The other figures, in particular the beautiful plates with foraminiferal images, should be included in the paper, either as genuine Figures or as Appendices. I also recommend to polish up the plates in that the specimens should be oriented in the usual way with the aperture up, brought to the same scale, and arranged in an artistic manner, same as in most taxonomic papers. The images are so beautiful, they simply deserve it. Giuliana Panieri may give advise, she knows how to do that.

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Citation: https://doi.org/10.5194/egusphere-2026-133-RC2

Pierre-Antoine Dessandier, Giuliana Panieri, Riwan Leroux, Ewan Pelleter, Sandra Fuchs, Alizé Bouriat, Audrey Boissier, Sandrine Cheron, and Jozée Sarrazin

Supplement

https://doi.org/10.5194/egusphere-2026-133-supplement

Pierre-Antoine Dessandier, Giuliana Panieri, Riwan Leroux, Ewan Pelleter, Sandra Fuchs, Alizé Bouriat, Audrey Boissier, Sandrine Cheron, and Jozée Sarrazin

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Short summary

This study focuses on foraminiferal distribution in the Luck Strike vent field, one of the most studied hydrothermal vents. Our results demonstrate that diversity increased where vent-derived particles are mixed with pelagic sedimentation, as it's the case in seafloor massive sulfide targeted for deep-sea mining by the industry. This study also revealed the impact of microbial biofilms on carbon budget though carbonate dissolution.


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