Cryoconite holes (water reservoirs) significantly contribute to biodiversity and biogeochemical processes on glacier surfaces. However, the lack of seasonal observations of cryoconite biota limits our knowledge of glacial ecosystem functioning. We studied photoautotrophs, consumers and sediment characteristics (community structure, biomass, elemental composition, organic matter content, δ13C, δ15N) from cryoconite holes in the upper and lower parts of the Forni Glacier ablation zone (Italy) throughout the ablation season. Dominant cyanobacteria were Oscillatoriaceae and Leptolyngbyaceae, while dominant green algae were Zygnemataceae and Chlorellaceae. Tardigrades (Cryobiotus klebelsbergi) were the dominant consumers. The biomass of consumers negatively correlated with the biomass of green algae, indicating that grazing likely controls algal communities in the upper part. Green algae dominated the upper part, while a shift from green algae- to cyanobacteria-dominated communities was observed in the lower part during the season. The increase in δ13C of cryoconite organic matter (OM) in the lower part followed the trend of the community shift of photoautotrophs potentially affected by precipitation. Also, δ13C of tardigrades positively correlated with δ13C of cryoconite OM in the upper part, indicating some cryoconite OM as their food. Some photoautotrophic taxa appeared only on specific dates, and no spatio-temporal changes in the cryoconite general elemental composition were found. Our data indicate that changes in the community structure and biomass of cryoconite biota on the Forni Glacier likely depend on the interplay between phenology, stochastic events (e.g., rainfall) and top-down or bottom-up controls. We demonstrate that multiple observations are essential for understanding the ecology of biota inhabiting cryoconite holes throughout the ablation season.

Department of Analytical Chemistry Faculty of Chemistry Adam Mickiewicz University Poznań Poland

Department of Animal Taxonomy and Ecology Faculty of Biology Adam Mickiewicz University Poznań Poland

Department of Botany and Plant Ecology Wrocław University of Environmental and Life Science Wrocław Poland

Department of Earth and Environmental Sciences University of Milano Bicocca Milan Italy

Department of Ecology Faculty of Science Charles University Prague Czech Republic

Department of Environmental Science and Policy University of Milan Milan Italy

Department of Water Protection Faculty of Biology Adam Mickiewicz University Poznań Poland

Institute of Geochemistry Mineralogy and Mineral Resources Faculty of Science Charles University Prague Czech Republic

See more in PubMed

Azzoni, R. S. , Senese A., Zerboni A., Maugeri M., Smiraglia C., and Diolaiuti G. A.. 2016. “Estimating Ice Albedo From Fine Debris Cover Quantified by a Semi‐Automatic Method: The Case Study of Forni Glacier, Italian Alps.” Cryosphere 10: 665–679. 10.5194/tc-10-665-2016. DOI

Bosson, J. B. , Huss M., Cauvy‐Fraunié S., et al. 2023. “Future Emergence of New Ecosystems Caused by Glacial Retreat.” Nature 620: 562–569. 10.1038/s41586-023-06302-2. PubMed DOI

Brodie, C. R. , Leng M. J., Casford J. S., et al. 2011. “Evidence for Bias in C and N Concentrations and 13C Composition of Terrestrial and Aquatic Organic Materials due to Preanalysis Acid Preparation Methods.” Chemical Geology 282: 67–83. 10.1016/j.chemgeo.2011.01.007. DOI

Bryndová, M. , Stec D., Schill R. O., Michalczyk Ł., and Devetter M.. 2020. “Dietary Preferences and Diet Effects on Life‐History Traits of Tardigrades.” Zoological Journal of the Linnean Society 188: 865–877. 10.1093/zoolinnean/zlz146. DOI

Buda, J. , Łokas E., Pietryka M., et al. 2020. “Biotope and Biocenosis of Cryoconite Hole Ecosystems on Ecology Glacier in the Maritime Antarctic.” Science of the Total Environment 724: 138112. 10.1016/j.scitotenv.2020.138112. PubMed DOI

Cameron, K. A. , Hodson A. J., and Osborn M.. 2012. “Carbon and Nitrogen Biogeochemical Cycling Potentials of Supraglacial Cryoconite Communities.” Polar Biology 35: 1375–1393. 10.1007/s00300-012-1178-3. DOI

Citterio, M. , Diolaiuti G., Smiraglia C., Verza G. P., and Meraldi E.. 2007. “Initial Results From the Automatic Weather Station (AWS) on the Ablation Tongue of Forni Glacier (Upper Valtellina, Italy).” Geografia Fisica e Dinamica Quaternaria 30: 141–151.

Dastych, H. , Kraus J., and Thaler K.. 2003. “Redescription and Notes on the Biology of the Glacier Tardigrade Hypsibius Klebelsbergi Mihelcic, 1959 (Tardigrada), Based on Material From Ötztal Alps, Austria.” Mitteilungen aus dem Hamburgischen Zoologischen Museum und Institut 100: 77–100.

Crosta, A. , Valle B., Caccianiga M., et al. 2025. “Ecological Interactions in Glacier Environments: A Review of Studies on a Model Alpine Glacier.” Biological Reviews 100: 227–244. PubMed PMC

Di Mauro, B. , Garzonio R., Baccolo G., et al. 2020. “Glacier Algae Foster Ice‐Albedo Feedback in the European Alps.” Scientific Reports 10, no. 1: 4739. PubMed PMC

Dubnick, A. , Wadham J., Tranter M., et al. 2017. “Trickle or Treat: The Dynamics of Nutrient Export From Polar Glaciers.” Hydrological Processes 31: 1776–1789. 10.1002/hyp.11149. DOI

Franzetti, A. , Navarra F., Tagliaferri I., et al. 2017. “Potential Sources of Bacteria Colonizing the Cryoconite of an Alpine Glacier.” PLoS One 12: e0174786. 10.1371/journal.pone.0174786. PubMed DOI PMC

Frossard, J. , and Renaud O.. 2019. “permuco: Permutation Tests for Regression, (Repeated Measures) ANOVA/ANCOVA and Comparison of Signals.” R package version 1.1.0. https://CRAN.R‐project.org/package=permuco.

Gobbi, M. , Ambrosini R., Casarotto C., et al. 2021. “Vanishing Permanent Glaciers: Climate Change Is Threatening a European Union Habitat (Code 8340) and Its Poorly Known Biodiversity.” Biodiversity and Conservation 30: 2267–2276. 10.1007/s10531-021-02185-9. DOI

Guidetti, R. , Bonifacio A., Altiero T., Bertolani R., and Rebecchi L.. 2015. “Distribution of Calcium and Chitin in the Tardigrade Feeding Apparatus in Relation to Its Function and Morphology.” Integrative and Comparative Biology 55, no. 2: 241–252. PubMed

Hallas, T. E. , and Yeates G. W.. 1972. “Tardigrada of the Soil and Litter of a Danish Beech Forest.” Pedobiologia 12: 287–304.

Hodson, A. J. , Sabacka M., Dayal A., et al. 2021. “Marked Seasonal Changes in the Microbial Production, Community Composition, and Biogeochemistry of Glacial Snowpack Ecosystems in the Maritime Antarctic.” Journal of Geophysical Research: Biogeosciences 126, no. 7: e2020JG005706.

Huot, Y. , Babin M., Bruyant F., Grob C., Twardowski M. S., and Claustre H.. 2007. “Does Chlorophyll a Provide the Best Index of Phytoplankton Biomass for Primary Productivity Studies?” Biogeosciences Discussions 4: 707–745. 10.5194/bgd-4-707-2007. DOI

Hutorowicz, A. 2013. “Ocena stanu ekologicznego jezior z wykorzystaniem fitoplanktonu.” In Biologiczne metody oceny stanu Środowiska, edited by Ciecierska H. and Dynowska M. (in Polish).tom 2, Ekosystemy wodne. Mantis, Olsztyn.

Jaroměřská, T. N. , Ambrosini R., and Mazurkiewicz M.. 2023. “Spatial Distribution and Stable Isotopic Composition of Invertebrates Uncover Differences Between Habitats on the Glacier Surface in the Alps.” Limnology 24, no. 2: 83–93.

Kindt, R. , and Coe R.. 2005. Tree Diversity Analysis. A Manual and Software for Common Statistical Meods for Ecological and Biodiversity Studies. World Agroforestry Centre (ICRAF) 92‐9059‐179‐X.

Lürling, M. , Eshetu F., Faassen E. J., Kosten S., and Huszar V. L.. 2013. “Comparison of Cyanobacterial and Green Algal Growth Rates at Different Temperatures.” Freshwater Biology 58, no. 3: 552–559.

Mihelcic, F. 1959. “Zwei neue Tardigraden aus der Gattung Hypsibills THULlN aus Osttirol (Osterreich), Systematisches zur Gattung Hypsibius THULlN.” Zoologischer Anzeiger 163: 254–261.

Musilova, M. , Tranter M., Bennett S. A., Wadham J., and Anesio A. M.. 2015. “Stable Microbial Community Composition on the Greenland Ice Sheet.” Frontiers in Microbiology 6: 193. 10.3389/fmicb.2015.00193. PubMed DOI PMC

Nalley, J. O. , O'Donnell D. R., and Litchman E.. 2018. “Temperature Effects on Growth Rates and Fatty Acid Content in Freshwater Algae and Cyanobacteria.” Algal Research 35: 500–507.

Novotná Jaroměřská, T. , Trubač J., Zawierucha K., Vondrovicová L., Devetter M., and Žárský J. D.. 2021. “Stable Isotopic Composition of Top Consumers in Arctic Cryoconite Holes: Revealing Divergent Roles in a Supraglacial Trophic Network.” Biogeosciences 18: 1543–1557. 10.5194/bg-18-1543-2021. DOI

Oksanen, J. 2020. “vegan: Community Ecology Package.” R package version 2.5–7. https://CRAN.R‐project.org/package=vegan.

Pittino, F. , Maglio M., Gandolfi I., et al. 2018. “Bacterial Communities of Cryoconite Holes of a Temperate Alpine Glacier Show Both Seasonal Trends and Year‐To‐Year Variability.” Annals of Glaciology 59: 1–9. 10.1017/aog.2018.16. DOI

Poniecka, E. A. , Bagshaw E. A., Sass H., et al. 2020. “Physiological Capabilities of Cryoconite Hole Microorganisms.” Frontiers in Microbiology 11: 1783. 10.3389/fmicb.2020.01783. PubMed DOI PMC

R Development Core Team . 2018. “R: a language and environment for statistical computing, Vienna, Austria.” www. R‐project.org (last access: 20 April 2023).

Roszkowska, M. , Wojciechowska D., Kmita H., et al. 2021. “Tips and Tricks How to Culture Water Bears: Simple Protocols for Culturing Eutardigrades (Tardigrada) Under Laboratory Conditions.” European Zoological Journal 88: 449–465. 10.1080/24750263.2021.1881631. DOI

Rozwalak, P. , Podkowa P., Buda J., et al. 2022. “Cryoconite – From Minerals and Organic Matter to Bioengineered Sediments on glacier's Surfaces.” Science of the Total Environment 807: 150874. 10.1016/j.scitotenv.2021.150874. PubMed DOI

Sanyal, A. , Antony R., Samui G., and Thamban M.. 2024. “Autotrophy to Heterotrophy: Shift in Bacterial Functions During the Melt Season in Antarctic Cryoconite Holes.” Journal of Microbiology 1− 19: 591–609. 10.1007/s12275-024-00140-1. PubMed DOI

Säwström, C. , Mumford P., Marshall W., Hodson A., and Laybourn‐Parry J.. 2002. “The Microbial Communities and Primary Productivity of Cryoconite Holes in an Arctic Glacier (Svalbard 79° N).” Polar Biology 25: 591–596. 10.1007/s00300-002-0388-5. DOI

Schmidt, S. K. , Johnson B. W., Solon A. J., et al. 2022. “Microbial Biogeochemistry and Phosphorus Limitation in Cryoconite Holes on Glaciers Across the Taylor Valley, McMurdo Dry Valleys, Antarctica.” Biogeochemistry 158: 313–326. 10.1007/s10533-022-00900-4. DOI

Senese, A. , Manara V., Maugeri M., and Diolaiuti G. A.. 2020. “Comparing Measured Incoming Shortwave and Longwave Radiation on a Glacier Surface With Estimated Records From Satellite and off‐Glacier Observations: A Case Study for the Forni Glacier, Italy.” Remote Sensing 12: 3719. 10.3390/rs12223719. DOI

Senese, A. , Maugeri M., Meraldi E., et al. 2018. “Estimating the Snow Water Equivalent on a Glacierized High Elevation Site (Forni Glacier, Italy).” Cryosphere 12: 1293–1306. 10.5194/tc-12-1293-2018. DOI

Stibal, M. , Šabacká M., and Kaštovská K.. 2006. “Microbial Communities on Glacier Surfaces in Svalbard: Impact of Physical and Chemical Properties on Abundance and Structure of Cyanobacteria and Algae.” Microbial Ecology 52: 644–654. 10.1007/s00248-006-9083-3. PubMed DOI

Stibal, M. , Šabacká M., and Žárský J.. 2012a. “Biological Processes on Glacier and Ice Sheet Surfaces.” Nature Geoscience 5: 771–774. 10.1038/ngeo1611. DOI

Stibal, M. , Telling J., Cook J., Mak K. M., Hodson A., and Anesio A. M.. 2012b. “Environmental Controls on Microbial Abundance and Activity on the Greenland Ice Sheet: A Multivariate Analysis Approach.” Microbial Ecology 63: 74–84. 10.1007/s00248-011-9935-3. PubMed DOI

Stibal, M. , and Tranter M.. 2007. “Laboratory Investigation of Inorganic Carbon Uptake by Cryoconite Debris From Werenskioldbreen, Svalbard.” Journal of Geophysical Research: Biogeosciences 112: G4. 10.1029/2007JG000429. DOI

Takeuchi, N. 2001. “The Altitudinal Distribution of Snow Algae on an Alaska Glacier (Gulkana Glacier in the Alaska Range).” Hydrological Processes 15: 3447–3459. 10.1002/hyp.1040. DOI

Takeuchi, N. 2013. “Seasonal and Altitudinal Variations in Snow Algal Communities on an Alaskan Glacier (Gulkana Glacier in the Alaska Range).” Environmental Research Letters 8: 035002. 10.1088/1748-9326/8/3/035002. DOI

Takeuchi, N. , Kohshima S., and Seko K.. 2001. “Structure, Formation, and Darkening Process of Albedo‐Reducing Material (Cryoconite) on a Himalayan Glacier: A Granular Algal Mat Growing on the Glacier.” Arctic, Antarctic, and Alpine Research 33: 115–122. 10.1080/15230430.2001.12003413. DOI

Takeuchi, N. , Tanaka S., Konno Y., Irvine‐Fynn T. D., Rassner S. M., and Edwards A.. 2019. “Variations in Phototroph Communities on the Ablating Bare‐Ice Surface of Glaciers on Brøggerhalvøya, Svalbard.” Frontiers in Earth Science 7: 4. 10.3389/feart.2019.00004. DOI

Telling, J. , Stibal M., Anesio A. M., et al. 2012. “Microbial Nitrogen Cycling on the Greenland Ice Sheet.” Biogeosciences 9: 2431–2442. 10.5194/bg-9-2431-2012. DOI

Uetake, J. , Naganuma T., Hebsgaard M. B., Kanda H., and Kohshima S.. 2010. “Communities of Algae and Cyanobacteria on Glaciers in West Greenland.” Polar Science 4: 71–80. 10.1016/j.polar.2010.03.002. DOI

Uetake, J. , Tanaka S., Segawa T., et al. 2016. “Microbial Community Variation in Cryoconite Granules on Qaanaaq Glacier, NW Greenland.” FEMS Microbiology Ecology 92: fiw127. 10.1093/femsec/fiw127. PubMed DOI

Velázquez, D. , Jungblut A. D., Rochera C., Rico E., Camacho A., and Quesada A.. 2017. “Trophic Interactions in Microbial Mats on Byers Peninsula, Maritime Antarctica.” Polar Biology 40: 1115–1126. 10.1007/s00300-016-2039-2. DOI

Vindušková, O. , Jandová K., and Frouz J.. 2019. “Improved Method for Removing Siderite by In Situ Acidification Before Elemental and Isotope Analysis of Soil Organic Carbon.” Journal of Plant Nutrition and Soil Science 182: 82–91. 10.1002/jpln.201800164. DOI

Vonnahme, T. R. , Devetter M., Žárský J. D., Šabacká M., and Elster J.. 2016. “Controls on Microalgal Community Structures in Cryoconite Holes Upon High‐Arctic Glaciers, Svalbard.” Biogeosciences 13: 659–674. 10.5194/bg-13-659-2016. DOI

Wejnerowski, Ł. , Poniecka E., Buda J., et al. 2023. “Empirical Testing of Cryoconite Granulation: Role of Cyanobacteria in the Formation of Key Biogenic Structure Darkening Glaciers in Polar Regions.” Journal of Phycology 59, no. 5: 939–949. PubMed

Wharton, R. A. , McKay C. P., Simmons G. M., and Parker B. C.. 1985. “Cryoconite Holes on Glaciers.” Bioscience 35: 499–503. 10.2307/1309818. PubMed DOI

Williamson, C. J. , Cook J., Tedstone A., et al. 2020. “Algal Photophysiology Drives Darkening and Melt of the Greenland Ice Sheet.” Proceedings. National Academy of Sciences. United States of America 117: 5694–5705. 10.1073/pnas.1918412117. PubMed DOI PMC

Winkel, M. , Trivedi C. B., Mourot R., Bradley J. A., Vieth‐Hillebrand A., and Benning L. G.. 2022. “Seasonality of Glacial Snow and Ice Microbial Communities.” Frontiers in Microbiology 13: 876848. 10.3389/fmicb.2022.876848. PubMed DOI PMC

Winkler, A. M. , Ridgway G. R., Webster M. A., Smith S. M., and Nichols T. E.. 2014. “Permutation Inference for the General Linear Model.” NeuroImage 92: 381–397. 10.1016/j.neuroimage.2014.01.060. PubMed DOI PMC

Yallop, M. L. , Anesio A. M., Perkins R. G., et al. 2012. “Photophysiology and Albedo‐Changing Potential of the Ice Algal Community on the Surface of the Greenland Ice Sheet.” ISME Journal 6: 2302–2313. 10.1038/ismej.2012.107. PubMed DOI PMC

Zawierucha, K. , Baccolo G., Di Mauro B., Nawrot A., Szczuciński W., and Kalińska E.. 2019b. “Micromorphological Features of Mineral Matter From Cryoconite Holes on Arctic (Svalbard) and Alpine (The Alps, the Caucasus) Glaciers.” Polar Science 22: 100482.

Zawierucha, K. , Buda J., and Nawrot A.. 2019a. “Extreme Weather Event Results in the Removal of Invertebrates From Cryoconite Holes on an Arctic Valley Glacier (Longyearbreen, Svalbard).” Ecological Research 34: 370–379. 10.1111/1440-1703.1276. DOI

Zawierucha, K. , Buda J., Pietryka M., et al. 2018. “Snapshot of Micro‐Animals and Associated Biotic and Abiotic Environmental Variables on the Edge of the South‐West Greenland Ice Sheet.” Limnology 19: 141–150. 10.1007/s10201-017-0528-9. DOI

Zawierucha, K. , Trzebny A., Buda J., et al. 2022. “Trophic and Symbiotic Links Between Obligate‐Glacier Water Bears (Tardigrada) and Cryoconite Microorganisms.” PLoS One 17: e0262039. 10.1371/journal.pone.0262039. PubMed DOI PMC

Zawierucha, K. , Vecchi M., Takeuchi N., Ono M., and Calhim S.. 2023. “Negative Impact of Freeze–Thaw Cycles on the Survival of Tardigrades.” Ecological Indicators 154: 110460. 10.1016/j.ecolind.2023.110460. DOI

Zemp, M. , Haeberli W., Hoelzle M., and Paul F.. 2006. “Alpine Glaciers to Disappear Within Decades?” Geophysical Research Letters 33: L13504. 10.1029/2006GL026319. DOI

Zawierucha, K. , Porazinska D. L., Ficetola G. F., et al. 2021. “A Hole in the Nematosphere: Tardigrades and Rotifers Dominate the Cryoconite Hole Environment, Whereas Nematodes Are Missing.” Journal of Zoology 313, no. 1: 18–36. 10.1111/jzo.12832. DOI