13th European Diatom Meeting Progress in Diatom Biogeography: Explanations for Microbial Endemism 2-4 March 2021 Amgueddfa Cymru – National Museum Wales Online - https://naturalhistory.museumwales.ac.uk/conference/edm
Programme and Abstracts
Dear Participants, We would like to welcome you to the 13th European Diatom Meeting (formerly Central European Diatom Meeting) to be held at Amgueddfa Cymru – National Museum Wales, St Fagans National Museum of History, Cardiff, United Kingdom. We are delighted to host the first online European Diatom Meeting with over 270 participants from more than 40 countries around the world. Amgueddfa Cymru – National Museum Wales is a major centre for taxonomic research and has the largest and most comprehensive collection of Welsh botany, zoology and geology specimens in the world. Our collections include over 3.5 million natural history specimens and provide a unique record of the natural history of Wales. St Fagans National Museum of History has completed its Making History redevelopment project in 2018. It is one of Wales’ most popular visitor attractions offering an exciting collection of historic buildings, heritage objects, and public programmes, to create history with the people of Wales. It is part of a 100-acre parkland with over forty original buildings from different historical periods. In 2019 it was declared the winner of the Art Fund Museum of the Year, the largest arts award in Britain. The Systematics Association of the United Kingdom has provided funding to support the 13th European Diatom Meeting. A special issue on biogeography will be published in the journal Diatom Research. Four keynote lectures will be presented on the major theme of the conference ‘Progress in Diatom Biogeography: Explanations for Microbial Endemism’. Historical biogeography in microbial organisms, especially many lower eukaryote groups, is not particularly well developed. In 2009, The Systematics Association addressed some general issues on this subject with a symposium and a book ‘Biogeography of Microscopic Organisms: Is Everything Small Everywhere?’, (D. Fontaneto, ed.), Cambridge, Cambridge University Press (2011). For the last three decades diatom systematists have been documenting the extent of diatom endemism, a topic previously thought to be of little significance. It is now clear that diatom endemism is extensive (Everything Small Isn’t Everywhere) and certain patterns of taxon differentiation exist, especially in the southern hemisphere. The meeting aims to discuss what the discovery of diatom endemism might mean in the context of the global historical biogeography of all organisms, addressing issues concerning freshwater diatom endemism and its explanation, biogeography in the marine realm and the influence of ecology and palaeoecology on the distributional limits of individual species. Oral and poster presentations are taking place on the 2nd and 3rd March 2021 covering topics including diatom biogeography, environmental monitoring, palaeoecology, biodiversity, morphology, molecular biology and taxonomy. A one-day taxonomic workshop on the complex of species in the Fragilaria capucina group takes place on the 4th March 2021 with lectures and microscope sessions. On behalf of the Organizing Committee, we wish you a pleasant time and an interesting meeting. Ingrid Jüttner & David M. Williams
Programme Tuesday 2nd March 2021 Time: GMT 9.00 – 9.20 Welcome address Kath Davies Ingrid Jüttner David Williams
Session 1 – Freshwater monitoring Chairs – Zlatko Levkov, Ingrid Jüttner
9.20 – 9.40 Martyn Kelly, Steve Juggins, Geoff Phillips, Nigel Willby The search for the perfect river: re-evaluating expectations for phytobenthos assessment in the UK 9.40 – 10.00 Annika Vilmi, Satu Maaria Karjalainen, Jukka Aroviita A decade of lake and stream diatom sampling: temporal trends and land use impacts 10.00 – 10.20 Bart Van de Vijver, Adrienne Mertens, Carlos E. Wetzel, Luc Ector How type material revision can influence biomonitoring analysis: a case study of Fragilaria capucina
10.20 – 10.50 Break
10.50 – 11.00 Stijn Van de Vondel, Lieven Bervoets, Bart Van de Vijver (Poster) Assessment of biological activity along a metal pollution gradient applying macroinvertebrates and diatoms 11.00 – 11.10 Petra Thea Mutinova, Maria Kahlert, Benjamin Kupilas, Brendan G. McCie, Nikolai Friberg, Francis J. Burdon (Poster) Benthic Diatom Communities in Urban Streams and the Role of Riparian Buffers
11.10 – 11.20 Wolfgang Küfner, Andrea Hofmann, Stefan Ossyssek, Jürgen Geist, Uta Raeder (Poster) Climate change in Bavarian mountain lakes – differential diatom responses among different lakes
11.20 – 11.40 Kálmán Tapolczai, François Keck, Agnès Bouchez, Frédéric Rimet, Maria Kahlert, Valetin Vasselon Strategies to handle taxonomic and bioinformatical biases in metabarcoding-based diatom indices.
11.40 – 11.50 Zlatko Levkov Announcement – 14th European Diatom Meeting in North Macedonia
11.50 – 12.00 Bart Van de Vijver Announcement – 15th European Diatom Meeting in Belgium
12.00 – 14.00 Break
Session 2 – Biogeography of marine diatoms Chairs – Eveline Pinseel, Ingrid Jüttner
14.00 – 14.50 Keynote lecture Jenny Pike Diatoms from the sub-polar North Atlantic: variations through time and space 14.50 – 15.10 Geraldine Reid Endemism in marine diatoms 15.10 – 15.30 Eveline Pinseel, Teovil Nakov, Koen Van den Berge, Kala Downey, Karthryn Judy, Olga Kourtchenko, Anke Krempf, Elisabeth Ruck, Conny Sjöqvist, Mats Töpel, Andrew J. Alverson Transcriptional response of the marine diatom Skeletonema marinoi during acclimation along a salinity gradient 15.30 – 15.40 Jason Hall-Spencer, Ben Harvey, Shigeki Wada, Sylvain Agostini (Poster) Diatoms thrive in areas where seawater has naturally high levels of carbon dioxide
15.40 – 16.10 Break
Session 3 – Palaeoecology Chairs – Eveline Pinseel, Ingrid Jüttner
16.10 – 17.00 Keynote lecture Anson Mackay Long term trends in diatom diversity from Lake Baikal, southern Siberia: a 15,800 year multidecadal study
17.00 – 17.20 Catarina Ritter, Pedro Miguel Raposeiro, Sergi Pla-Rabes, Erik de Boer, Armand Hernández, Alberto Sáez, Nora Richter, Linda Amaral-Zettler, Mario Benavente-Marín, Ricardo Trigo, Roberto Bao, Santiago Giralt, Vítor Gonçalves The last millennium of natural and anthropogenic disturbances on a remote island on the edge of Europe: a diatom-based paleolimnological approach
Wednesday 3rd March 2021 Session 4 – Diatom Taxonomy Chairs – Carlos Wetzel, Ingrid Jüttner
9.00 – 9.20 Eileen Cox Generic concepts, the type method and descriptive terminology 9.20 – 9.40 Nélida Abarca, Jonas Zimmermann, Wolf-Henning Kusber, Oliver Skibbe, Regine Jahn Taxon complexes within the Gomphonemataceae: evaluation of morphological and molecular data 9.40 – 10.00 Konrad Schultz, Josephine Franke, Mirko Dreßler, Thomas Hübener Colony formation in Stephanodiscus and Cyclostephanos: morphological and taxonomic implications
10.00 – 10.20 Break
10.20 – 10.30 Edgley César, Jo Wilbraham, David Williams (Poster) Diatom Collections at the Natural History Museum: Using digitisation to maximise research potential
10.30 – 10.40 Malin Alf, Thomas Hübener, Konrad Schultz, Mirko Dressler (Poster) Identification of Cyclostephanos species using molecular and morphological methods
10.40 – 10.50 Josephine Franke, Thomas Hübener, Konrad Schultz, Mirko Dressler (Poster) Molecular and morphometric analyses of the Cyclotella meneghiniana species complex
10.50 – 11.20 Break
Session 5 – Freshwater diatom biodiversity and distribution Chairs – David Williams, Ingrid Jüttner
11.20 – 11.40 Lydia King, Marco Cantonati, Wolfgang Schütz Diatom depth distribution in the large peri-alpine Lake Constance 11.40 – 12.00 Ingrid Jüttner, Smriti Gurung, Anu Gurung, Chhatra Sharma, Subodh Sharma Diatom diversity in high altitude lakes of the Himalaya 12.00 – 12.10 Jordan Bishop, Jane Wasley, Melinda Waterman, Tyler J. Kohler, Bart Van de Vijver, Sharon Robinson, Kateřina Kopalová (Poster) Epiphytic diatom community shows larger response to bryophyte and lichen vegetation type than nutrient and water additions within Windmill Islands, East Antarctica
12.10 – 12.20 Leila Ben Khelifa (Poster) Diatom flora of Tunisia
12.20 – 12.30 Tereza Cahová, Barbora Chattová, Bart Van de Vijver (Poster) Soil diatom communities of Amsterdam Island (TAAF, South Indian Ocean)
12.30 – 12.40 Jasper Foets, Carlos E. Wetzel, Adriaan J. Teuling, Lauren Pfister (Poster) Ecohydrological characterization of terrestrial diatoms
12.40 – 12.50 Charlotte Goeyers, Bart Van de Vijver (Poster) Moss-inhabiting diatoms from Campbell Island (sub-Antarctic Region)
12.50 – 13.00 Maili Lehtpuu, Sirje Vilbaste (Poster) Benthic diatoms in small Estonian lakes – two substratum type comparsion
13.00 – 13.10 Danijela Vidaković, Jelena Krizmanić, Luc Ector, Carlos Wetzel, Bojan Gavrilović, Miloš Ćirić (Poster) Nitzschia species from inland saline waters in the Vojvodina Province (Serbia)
13.10 – 14.00 Break
Session 6 – Biogeography of freshwater diatoms Chairs – Martyn Kelly, Ingrid Jüttner
14.00 – 14.20 David Williams Diatom biogeography: is there a point to it? 14.20 – 15.10 Keynote lecture Janne Soininen Diatom biogeography – new insights from species distribution and biodiversity analyses
15.10 – 15.50 Break
Session 6 – Biogeography of freshwater diatoms Chairs – Martyn Kelly, Ingrid Jüttner
15.50 – 16.10 David Mann The interpretation of absence revisited: the challenges of establishing alien status and biogeographical range 16.10 – 17.00 Keynote lecture Patrick Kociolek Freshwater diatom biogeography: a phylogenetic approach 17.00 – 18.00 Discussion – the road ahead: how to combine taxonomy, ecology and biogeography
Thursday 4th March 2021 Workshop on the Fragilaria capucina complex Bart Van de Vijver, Meise Botanic Garden, Belgium Adrienne Mertens, Diatomella, Netherlands Luc Ector, Carlos Wetzel, Luxembourg Institute of Science and Technology, Luxembourg
The workshop on the complex of species in the Fragilaria capucina group will consist of two parts. During the morning sessions, lectures will document and discuss all species in this group. In the afternoon, selected species will be illustrated using light microscopy and material from type slides and other populations from Europe.
9.00 – 10.00 Lecture 1 10.00 – 10.30 Break 10.30 – 12.00 Lecture 2 12.00 – 13.00 Break 13.00 – 15.00 Microscope session
Keynote presentations
Didymosphenia
Freshwater diatom biogeography: a phylogenetic perspective Patrick Kociolek University of Colorado Museum of Natural History and Department of Ecology and Evolutionary Biology Boulder, Colorado, 80309, United States In this talk I will summarize some of the past and current approaches to studies on the distribution of freshwater diatom taxa, from the “Age of Cosmopolitanism” (which existed for nearly a century until the mid 1980’s) to the “Age of Endemism” (since the 1980’s). Examples of including a phylogenetic perspective to studies of freshwater diatom biogeography are presented, focusing on broad lineages of taxa (genera) and specific hotspots of diatom endemism. These studies highlight that certain places in the world, from scales of individual habitats to continental, may have much greater levels of endemism than others, and that lineages of diatoms may have greater endemism in certain places and parts of the world than others. An understanding of biogeographic patterns is explored using Antarctica (of all places) as a hotspot for endemism, using two genera as case studies. Finally, the talk will explore whether the distributions of diatoms are aligned with other groups of organisms, by examining the distribution of Surirella and Gomphonema species across Wallace’s Line. Challenges to more refined studies of freshwater diatom biogeography are presented.
Long term trends in diatom diversity from Lake Baikal, southern Siberia Anson Mackay1, Vivian Felde2, David Morley1, Virginia Panizzo5, Natalia Piotrowska3 Patrick Rioual4, Alistair Seddon2, George Swann5 1University College London, London, United Kingdom 2University of Bergen, Bergen, Norway 3Silesian University of Technology, Gliwice, Poland 4Institute of Geology & Geophysics, Beijing, China 5University of Nottingham, Nottingham, United Kingdom Lake Baikal is the world’s oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the “most outstanding example of a freshwater ecosystem” and designated a World Heritage Site in 1996 due to its high level of endemicity, biodiversity in the lake remains increasingly threatened by both climate change and anthropogenic disturbance. Biological diversity in of itself, is inextricably linked to community stability and ecosystem functioning, but our understanding of these relationships in freshwater ecosystems is largely based on short-term observational, experimental, and modelling approaches. Using a multidecadal diatom record for the past 15,800 years from Lake Baikal, we investigate how two ecosystem components – diversity and productivity - have responded to climate changes on long-timescales. In Lake Baikal, diatom community dynamics have benefited enormously from extensive monitoring work carried out over many decades. In this talk we will also explore how we can 30 use stable isotope analyses of diatom frustules (δ Sidiatom), to investigate the influence of nutrient cycling to diatom community dynamics over recent millennia, and what this may mean for our interpretations of diatom changes during abrupt climate events of the late glacial – early Holocene period.
Diatoms from the sub-polar North Atlantic: variations through time and space Jenny Pike School of Earth and Ocean Sciences, Cardiff University, Park Place Cardiff CF10 3AT, United Kingdom Marine diatoms are well-established as quantitative and qualitative proxies for past high latitude ocean conditions due to their sensitive habitat preferences for the sea ice zone, marginal ice zone, or the permanently open ocean. In the contemporary northern high latitudes, different assemblages of diatoms associated with different salinity, temperature and sea ice concentrations have been observed to contribute approximately 70% of the phytoplankton biomass during the spring bloom, greater than 50% of the summer sea ice-edge surface phytoplankton bloom and can also dominate the early spring ice-edge-associated subsurface chlorophyll maximum. As ice has thinned in the Arctic Ocean and reduced in extent, annual phytoplankton productivity has increased and under-ice phytoplankton blooms can become increasingly dominated by diatoms during the summer melt season. Further, the marine biological carbon pump can be strongest when diatoms dominate the phytoplankton and, thus, marine diatoms can strongly influence the flow of energy and carbon through the surface ocean ecosystem and the export of carbon into the deep ocean. These modern observations inform our interpretations of Late Quaternary fossil diatom assemblages from the North Atlantic region. Fossil diatom assemblages dominated by species of Rhizosolenia Brightwell can be used to monitor the past position of major oceanic frontal systems, such as the Polar Front and Subarctic Front, as they crossed the subpolar North Atlantic during the last deglaciation. Increased abundance of taxa such as Thalassiosira nordenskioeldii Cleve and Thalassiosira baltica (Grunow) Ostenfeld at sediment core sites south of Iceland and Greenland appear to indicate ice and water export into the subpolar Atlantic from the Labrador Sea and the Norwegian-Greenland Sea, respectively, during the break up and retreat of the glacial polar ice caps. Increased abundance of Shionodiscus oestrupii (Ostenfeld) Alverson, Kang & Theriot indicates increased volume of warm water being transported northwards into the subpolar gyre from the subtropical gyre. Thus, an understanding of the ecological preferences and biogeography of diatom assemblages, and individual taxa, can provide insights into the evolution of the size and position of the subpolar gyre and the waning influence of sea ice in the North Atlantic over the past 20000 years.
Diatom biogeography – new insights from species distribution and biodiversity analyses Janne Soininen Department of Geosciences and Geography, University of Helsinki, Finland Biogeographical research of microorganisms has attracted notable attention in recent decades. Most studies suggest that there are biogeographical patterns such as distance decay relationships or species richness gradients also in microorganisms largely similar to larger taxa. Here, I would discuss recent findings in biogeography of microbes, especially freshwater diatoms. I show that species distribution models widely used in macroecology of birds, mammals and plants are highly useful in studies of diatom niche conservatism (NC). I study whether NC is evident in stream diatom morphospecies by modeling species responses to environmental and climatic variables in a set of calibration sites from the US and then evaluate the models with five test regions. I also examine whether diatom species show congruency in environmental niche optima between the study regions. Results show that NC is low in both environmental and climate models as the models trained in the US have poor performance when transferred to other geographical regions. Diatom environmental and climatic optima varied clearly between the regions but showed some positive relationships especially for pH and total phosphorus. Results suggest that diatoms show overall relatively little NC globally, and NC was especially low for climatic variables. Collectively, these findings suggest that there may exist locally adapted lineages within the diatom morphospecies especially for differences in temperature. I end my talk discussing about how island biogeography of diatoms, especially that of island species-area relationship, may give further insights into potential dispersal limitation in diatoms and provides an interesting model system for testing classical bio- geographical patterns not probably revealed earlier in microorganisms.
Oral presentations
Frustulia
Taxon complexes within the Gomphonemataceae: evaluation of morphological and molecular data Nélida Abarca, Jonas Zimmermann, Wolf-Henning Kusber, Oliver Skibbe, Regine Jahn Botanic Garden and Botanical Museum Berlin, Freie Universität Berlin Königin-Luise-Straße 6-8, D-14195 Berlin, Germany Taxa within the genus Gomphonema Ehrenberg have long been recognized as highly variable complexes with broad ecological tolerances in which many species, varieties and forms have been described. Differences amongst taxa, however, are hard to unravel because of morphological similarities and apparent high infra-specific variation. The current separation is mainly based on morphological characters of the valve, e.g., the pattern of the central area, density and branching of the striae, the shape or arrangement of the punctae, as well as the outline. In cases where morphological and ultrastructural characters are insufficient for species delimitation, molecular data can provide additional evidence on the significance of features which are important for integrative taxonomy. In order to differentiate taxa and to assess potential cryptic species, infraspecific variation and biogeographical distribution patterns, in our study uni-algal cultures identified as from the genus Gomphonema were isolated from environmental samples of Germany, Spain, France, Faroe Islands, Korea, and Mexico. They were studied by light and electron microscopy and showed overlapping and variable morphological characters within uni-algal cultures, pinpointing at the need to find more stable morphological characters. In addition, three molecular markers were tested on the cultures. The integrative taxonomic approach clarified which features belong to the genus Gomphonema and therefore which taxa may not do so. The outcome of this study shows that only a polyphasic approach, combining molecular and micromorphological data for taxonomy, nomenclatural evaluation, observations from clonal cultures, and ecology, will reveal the full intricacies of evolutionary relations within specific organism groups, laying the foundation for future evolutionary, taxonomical and ecological studies as well as the sound application in monitoring approaches using diatoms.
Generic concepts, the type method and descriptive terminology Eileen Cox The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom Diatom genera have been being described for almost 200 years, with the criteria on which they are defined changing as new techniques are developed. However, for nomenclatural reasons, when first defined, each genus is linked to a single species, the generitype and its characteristics are the basis of the generic description. Comparisons are usually then made between that generitype and other taxa (existing or newly discovered) to determine whether, or not, they belong in the same genus. There is then a tendency to expect close similarity to the generitype for allocation to that genus. But as with the type specimen of a species, the type is not invariably typical of the taxon as a whole, nor should we assume that the generitype is typical of the genus. Also, because diatom descriptive terminology is not standardised, formal written descriptions of similar taxa may differ simply through the language used. It is also important to ensure that appropriate comparisons are made, without inadvertent assumptions coming into play in the choice of comparative taxa. This talk will explore some of these issues, showing where contrasting terminology has separated potentially congeneric species, or where assumptions have limited relevant comparisons possibly leading to unnecessary generic proliferation.
Diatom diversity in high altitude lakes of the Himalaya Ingrid Jüttner1, Smriti Gurung2, Anu Gurung2, Chhatra M. Sharma3 Subodh Sharma2 1Amgueddfa Cymru – National Museum Wales, Department of Natural Sciences Cathays Park, Cardiff, United Kingdom 2Kathmandu University, Department of Environmental Science and Engineering Dhulikhel, Nepal 3Tribhuvan University, Central Department of Environmental Science Kirtipur, Nepal Alpine lakes are important ecosystems for biodiversity conservation and refuge habitats for many rare species. They are increasingly under threat from climate change, pollution and changes in catchment land use. Relatively few studies have been carried out on diatoms in lakes at high altitudes in the Himalaya. We provide a summary of our work in three regions of the Nepalese Himalaya, Rara Lake in the Rara Lake National Park of western Nepal, the Gosainkunda lakes in the Langtang National Park of central Nepal, and the Gokyo lakes in the Gokyo Valley of the Everest National Park in eastern Nepal. Surveys were conducted in autumn and spring in all areas, and diatoms were collected from all available substrata in the lakes’ littoral areas. Land use, season and substratum composition were factors that affected species composition. At Rara Lake, higher ion concentrations in spring were matched by higher abundance of more pollution tolerant species. Assemblage change between seasons at Gosainkunda probably reflected lower pH in spring after snow melt and release of accumulated pollutants from a major urban centre south of the lake area. At Rara Lake and at Gokyo, assemblages in some littoral areas reflected impacts of adjacent settlements. Natural vegetation and land cover in the catchments were also important factors and diatoms differed between littoral areas with adjacent alpine grassland, forest, Tundra grassland or boulder fields. Taxonomic investigations focused on species in the genera Gomphonema (Rara Lake), Oricymba (Gosainkunda), Cymbella, Cymbopleura, Achnanthidium (Gokyo). Species composition differed clearly between lake areas reflecting differences in altitude, geographic location, geology, water chemistry, land use and catchment vegetation. A much larger number of species and genera were found in Rara Lake and in the Gokyo Valley than in the lakes of Gosainkunda. Future studies will include taxonomic investigations of the genus Achnanthidium and the smaller fragilarioid taxa. In addition, studies across altitudes, regions and seasons would help understand which role climatic factors, pollution, land use and geology play for diatom distribution in Himalayan lakes.
The search for the perfect river: re-evaluating expectations for phytobenthos assessment in the UK Martyn Kelly1,2, Steve Juggins3, Geoff Phillips4, Nigel Willby4 1Bowburn Consultancy, 11 Monteigne Drive, Bowburn, Durham DH6 5QB, United Kingdom 2School of Geography, University of Nottingham, Nottingham NG7 2RD, United Kingdom 3School of Geography, Politics and Sociology, Newcastle University Newcastle NE1 7RU, United Kingdom 4Department of Biological and Environmental Sciences, University of Stirling Stirling FK9 4LA, United Kingdom The reference model underlying the UK phytobenthos (diatom) tool for Water Framework Directive assessments is revisited and a new approach is proposed which uses quantile regression to predict the lowest values of the Trophic Diatom Index (equating to the best attainable condition) at any level of alkalinity to be predicted. Whilst a reference model based on least disturbed or minimally impacted conditions would be preferable in theory, in practice the absence of lowland high alkalinity streams in a minimally impacted condition in the UK precludes the use of these approaches. Having proposed a revised reference model for phytobenthos, we then go on to examine the relationship between phytobenthos and macrophytes. These two groups respond to nutrients and other pressures in different ways with phytobenthos being more sensitive to nutrients whilst macrophytes better reflect the extent to which secondary effects are likely. We argue that averaging the two sub-elements of the “macrophytes and phytobenthos” biological quality element is a more realistic option than the current approach of taking the lower of the two assessments. It is, however, possible, to predict the value of the combined quality element from either sub-element, though we recognize that this also risks misclassifications unless supported by local knowledge of catchments.
Diatom depth distribution in the large peri-alpine Lake Constance Lydia King1, Marco Cantonati2, Wolfgang Schütz3 1Limnologie-Phykologie-Diatomologie, Basler Landstr. 54, Freiburg 79111, Germany 2MUSE – Museo delle Scienze, Limnology & Phycology Section Corso del Lavoro e della Scienza 3, Trento 38123, Italy 3Büro für Ökologie und Vegetationskunde, Im Jägeracker 28 Emmendingen 79312, Germany Apart from regularly conducted phytoplankton sampling in open water and diatom sampling from the littoral zone, the phytobenthos of Lake Constance (Germany) has received little attention (Oberdorfer, 1928; Mattern, 1970; Bahulikar 2007). The only known studies of benthic algae from greater depth go back 100 years, conducted by Lauterborn (1922) and Zimmermann (1927). They investigated the algal communities of the limestone-crust covered, steep molasse walls in Lake Überlingen. In general, still very little is known of the depth distribution of benthic diatoms in lakes (Cantonati et al. 2009, Cantonati & Lowe 2014) and Lake Constance has experienced dramatic changes during the last 100 years. Therefore, we went back to the sites of Lauterborn (1922) and Zimmermann (1927) and collected algal samples from down to 40 m depth of the molasse walls with the help of divers (AG Limnology, Karlsruhe) near Wallhausen in summer 2017 and near Überlingen in summer 2018. Samples were prepared and analysed following standard methodology and diatom communities of different depth compared using a similarity index. At greater depth Lauterborn (1922) found mainly Epithemia hyndmanni W. Smith and Melosira arenaria Moore. In the upper layers he discovered Epithemia argus Kütz. var. longicornis Grun. and growing on green algae Achnanthidium minutissimum Kütz., Cocconeis flexella Kütz., Gomphonema sp. and Cymbella sp. In greater depths he also noticed the epiphytes Gomphonema intricatum Kütz. var. pulvinatum A. Braun, Eunotia sp. and Cocconeis placentula. Gyrosigma attenuatum Kütz. and Diploneis elliptica Kütz. were identified by Lauterborn (1922) as rarely occuring at various depths (sic). Since then not only the nutrient levels have undergone dramatic changes (with eutrophication and recent oligotrophication), but also the zoobenthos community colonising the walls. Dreissena polymorpha and Dreissena rostriformis burgensis invaded the lake from the 1960s onwards and occupied almost the entire molasse walls, often several layers thick from the shoreline down to 30 m depth. The colourful patches formed by filamentous and crustous Chlorophyceae, Rhodophyceae, Phaeophyceae (Bodanella lauterborni) and Cyanophyceae, partially used as substratum by epiphytic diatoms 100 years ago, had disappeared. Therefore, it was very difficult to find any algal growth. Nevertheless, some samples contained sufficient diatoms to investigate differences between the two sites and various depths. A comparison of the species composition of the diatom samples using the similarity index showed: 1. the diatom communities of the two different sites were very similar, and 2. two distinct diatom communities exist above and below ca. 15 m depth. Down to ca. 15 m depth a diverse diatom community was found composed mostly by common taxa. In contrast, only approximately 15 taxa made up the diatom community of greater depths with mainly small celled (like Sellaphora nigri) and unusual taxa, e.g. Planothidium werumianum and very high abundances of a Nupela sp. which is under investigation. The interpretation of absence revisited: the challenges of establishing alien status and biogeographical range David Mann Royal Botanic Garden Edinburgh, Inverleith Row, Edinburgh Scotland EH3 5LR, United Kingdom There are increasing numbers of claims that particular diatom species have restricted geographical ranges, i.e. they are ‘endemic’ to a particular region. If there are indeed endemics, there could also, potentially, be ‘aliens’, i.e. species that originally had a particular restricted range because of dispersal constraints but have recently spread – as a result of human interventions overcoming those constraints – to new areas to which they are preadapted. There have indeed been claims for alien status, including for the freshwater benthic Didymosphenia geminata and planktonic Asterionella formosa in New Zealand, and for the marine planktonic Coscinodiscus wailesii and Trieres sinensis in the N Atlantic and North Sea. M. Coste & L. Ector (2000, Syst Geogr. Plants 70: 373-400) analysed a number of cases of species that had either become more abundant recently or been recorded for the first time recently in France, including Hydrosera triquetra (recorded from long ago but apparently increasing), and Gomphoneis minuta and Encyonema triangulum (both recorded for the first time in the 1990s). Detecting and explaining geographical ranges and range alterations is important if we are to understand how diatom diversity has arisen, whether changes in distributions reflect climate warming or not, and whether precautions need to be taken to avoid accidental transfers of cells. I will explore claims of restricted geographical range and ‘alien status’, and the criteria needed to establish such claims, by reference to four species recently recorded for the first time in the UK (which is arguably among the best-studied countries world-wide for diatom species diversity). These are the marine benthic species Diademoides luxuriosa, ‘Navicula’ entoleia and Nitzschia ocellata, and the subaerial freshwater diatom Denticula rainierensis. Of these only one can plausibly be argued, on the basis of light microscopical records, to have had a naturally restricted geographical range. This is the distinctive naviculoid diatom Diademoides luxuriosa, which seems to have had a circum-Pacific distribution before its discovery on Scottish coasts in 2014. This species seems to be the first known example of an alien benthic marine diatom. In contrast, although ‘Navicula’ entoleia and Nitzschia ocellata are both very distinctive species, records of them have been rare and sporadic and their distributions showed no clear geographical pattern both before and after their discovery in Scotland. Denticula rainierensis is an example of a diatom whose apparent distribution is probably an artefact of taxonomy, as may be the two ‘classic’ species of ‘invasive’ marine phytoplankton, Coscinodiscus wailesii and Trieres sinensis. Finally, the fact that many new species are being discovered in every part of the globe indicates that the observational basis for diatom biogeography is often weak; each case (i.e. each claimed species distribution) needs individual analysis and justification.
Transcriptional response of the marine diatom Skeletonema marinoi during acclimation along a salinity gradient
Eveline Pinseel1, Teofil Nakov1, Koen Van den Berge2,3,4, Kala Downey1, Kathryn Judy1 Olga Kourtchenko5, Anke Krempf6, Elizabeth Ruck1, Conny Sjöqvist7, Mats Töpel5 Andrew J. Alverson1
1Department of Biological Sciences, University of Arkansas, Fayetteville, AR, United States 2Department of Statistics, University of California, Berkeley, CA, United States 3Department of Applied Mathematics, Computer Science and Statistics, Ghent University Ghent, Belgium 4Bioinformatics Institute Ghent, Ghent University, Ghent, Belgium 5Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden 6Leibniz-Institute for Baltic Sea Research, Rostock, Germany 7Faculty of Science and Engineering, Åbo Akademi University, Turku, Finland The salinity gradient separating marine and freshwater environments represents one of the major ecological divides for diatoms, and is thought to be an important driver for diversification. Yet, the mechanisms by which marine diatoms adapt to, and ultimately diversify in, freshwater environments are poorly understood. Here, we investigate the transcriptional response of the ancestrally marine diatom Skeletonema marinoi during long- term exposure to low salinities, mimicking the Baltic Sea salinity cline along which S. marinoi naturally occurs. We found that S. marinoi substantially alters its metabolism in low salinities: cell division rates decreased, cells had higher energy demands, and they produced more storage compounds and fewer osmolytes. Inclusion of eight different culture strains revealed that different genotypes differ significantly in their response, both in the direction and magnitude of gene expression. These differences include fundamental cellular processes such as nuclear division, regulation of transcription and translation, and aerobic respiration. Of the 7 905 differentially expressed genes, only 27 were differentially expressed in each genotype, representing genes involved in oxidative stress management, potassium transmembrane transport, and carbohydrate, lipid and amino acid biosynthesis. Altogether, our results reveal substantial variation in the response of different genotypes, highlighting an important but often overlooked source of biological variation associated with how diatoms respond and adapt to environmental change.
Endemism in marine diatoms Geraldine Reid National Museums Liverpool, Department of Botany, World Museum, William Brown Street Liverpool, L3 8EN, United Kingdom Marine benthic diatom studies often feel like the poor relation of their freshwater counterparts. Understudied, unknown but diversely rich floras - can these be the key to understanding the biogeography of diatoms? Marine benthic diatoms and their patterns of endemism are explored.
The last millenium of natural and anthropogenic disturbances on a remote island on the edge of Europe: a diatom-based paleolimnological approach Catarina Ritter1, Pedro M. Raposeiro1, Sergi Pla-Rabes2, Erik J. de Boer3 Armand Hernández3, Alberto Sáez4, Nora Richter5, Linda Amaral-Zettler5,6,7 Mario Benavente-Marín3, Ricardo Trigo8, Roberto Bao9, Santiago Giralt3 Vítor Gonçalves1 1Centro de Investigação em Biodiversidade e Recursos Genéticos, CIBIO InBIO Laboratório Associado Pólo dos Açores & Faculdade de Ciências e Tecnologia da Universidade dos Açores, Ponta Delgada, Açores, Portugal
2CREAF & UAB, Cerdanyola del Vallès, Barcelona, Spain
3Institute of Earth Sciences Jaume Almera (ICTJA) Spanish National Research Council (CSIC), Barcelona, Spain
4Department of Earth and Ocean Dynamics, Universitat de Barcelona, Barcelona, Spain
5Department of Earth, Environmental, and Planetary Sciences Brown University Providence, USA
6Department of Marine Microbiology and Biogeochemistry NIOZ Royal Netherlands Institute for Sea Research, AB Den Burg, The Netherlands
7Department of Freshwater and Marine Ecology Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam The Netherlands
8Instituto Dom Luiz (IDL), Faculty of Sciences, University of Lisboa, Lisbon, Portugal
9Centro de Investigacións Científicas Avanzadas (CICA) - Facultade de Ciencias Universidade da Coruña, A Coruña, Spain Previous studies show that climate variability and volcanism along with the arrival of humans played a significant role in the recent evolution of insular Azorean ecosystems. However, the timing and rate of anthropogenic impacts are poorly understood. Paleolimnological research allows us to reconstruct ecological conditions prior to and after human settlement on oceanic islands, to understand how species and island ecosystems responded to both natural and anthropogenic disturbances. Here, we present the first high-resolution reconstruction of ecological changes in Lake Funda (Flores Island, Azores) over the last millennium based on diatom analysis from a 993 cm-long sediment core retrieved in June 2017. The chronology of the reconstructed paleoenvironmental events has been established with a preliminary radiocarbon-based age model. The three main ecological periods were mostly related to human disturbance. (1) During the pre-human arrival period (AD 950 to 1330), the sediment record has a diverse benthic and tychoplanktonic diatom assemblage dominated by Staurosirella pinnata and Pseudostaurosira elliptica, representing the baseline conditions of Lake Funda. (2) Upon human arrival in Flores, around AD 1330, human disturbances in the catchment area (e.g., livestock release and gradual forest clearance) and climate fluctuations led to changes in the diatom assemblage. Several climate fluctuations from AD 1330 to 1560 and the onset of human-driven deforestation (ca. 1380 AD) led to an abrupt drop in diatom diversity and the dominance of eutrophic Aulacoseira spp.. (3) Finally, the most recent period (AD 1560 to 2008) corresponds to the well-established Portuguese settlement in Flores Island. Complete forest clearance led to a second ecological perturbation characterized by a highly productive lake with an anoxic hypolimnion and enhanced in-lake nutrient recycling. From 1980, changes in diatom assemblages suggest prolonged periods of summer stratification and increase in extreme climatic events, which could be associated with recent climate change. The synergistic influence of multiple environmental stressors (climate and anthropogenic) may have resulted in major shifts in the diatom assemblages of Lake Funda. This study increases our understanding of how the interplay between climate and anthropogenic factors results in drastic shifts in lake ecosystems. The present paleolimnological approach has important implications for long-term ecosystems conservation management in remote volcanic oceanic islands. This research is funded by DISCOVERAZORES (PTDC/CTA-AMB/28511/2017; DL57/2016/ ICETA/EEC2018/25) and through the funded research project PaleoModes (CGL2016-75281-C2) and the Luso-American Foundation's "Crossing the Atlantic" program.
Colony formation in Stephanodiscus and Cyclostephanos: morphological and taxonomic implications Konrad Schultz, Josephine Franke, Mirko Dreßler, Thomas Hübener Department of Botany, University of Rostock, Wismarsche Straße 44/45, Rostock 18051 Mecklenburg-Vorpommern, Germany The genera Cyclostephanos and Stephanodiscus are among the most common and diverse groups of centric freshwater diatoms and thus play an important role in many freshwater planktonic communities worldwide. Although many species are solitary, obligatory and facultative forming of colonies is known for both genera. Those colonies are always chain-like and adjacent cells attach to each other by linking spines. While many of the solitary species can occasionally form short, more loose chains, we focused on those species that build longer chains held together with the help of special linking-spines. In this study, we used monoclonal strains to investigate the influence of colony-formation on the ultrastructure of the valves by gathering morphometrical data based on SEM images. Strains of the following obligatory or facultative colony-forming species were used: Stephanodiscus hantzschii, S. binderanus as well as Cyclostephanos delicatus and C. invisitatus. As a result, we found significant morphological differences between chain-forming and solitary strains of the same species. Valve face structure and striation are different in colony-forming strains. Because of the difference in morphology, DNA-barcoding was used to clarify the phylogenetic relationship between solitary and colony-forming strains. DNA-barcoding revealed no differences between the chain-forming and solitary strains and even showed identical sequences for S. hantzschii and S. binderanus, implying both species may actually be two different forms of the same facultative colony-forming species. In conclusion, we found significant morphological differences between solitary and colony-forming strains in strains of the same species. This has implications for the theoretical and applied taxonomy of these species. It broadens the morphological definitions of the investigated facultative colony-forming species and also challenges the taxonomical status of seemingly obligatory colony-forming species such as S. binderanus.
Strategies to handle taxonomical and bioinformatical biases in metabarcoding-based diatom indices Kálmán Tapolczai1, François Keck2, Agnès Bouchez2, Frédéric Rimet2, Maria Kahlert3 Valentin Vasselon4 1Department of Limnology, University of Pannonia and Hungarian Academy of Sciences Egyetem u. 10, Veszprém, H-8200, Hungary 2INRA, UMR CARRTEL, 75bis avenue de Corzent, Thonon-les-Bains 74200, France 3Department of Aquatic Sciences and Assessment Swedish University of Agricultural Sciences, Uppsala 750 07, Sweden 4AAFB, Pôle R&D “ECLA”, INRA, UMR CARRTEL, 75bis avenue de Corzent Thonon-les-Bains 74200, France Recent years provided intense progression in the implementation of molecular techniques in a wide variety of research fields in ecology. Biomonitoring and bioassessment can greatly benefit from DNA metabarcoding and High-Throughput Sequencing (HTS) methods that potentially provide reliable, high quantity and quality standardised data in a cost- and time-efficient way. However, DNA metabarcoding has its drawbacks, introducing biases at all the steps of the process, particularly during bioinformatics treatments used to prepare HTS data for ecological analyses. The high diversity of bioinformatics methods (e.g. OTU clustering, chimera detection, taxonomic assignment) and parameters (e.g. percentage similarity threshold used to define OTUs) make inter-studies comparison difficult, limiting the development of standardised and easy-accessible bioassessment procedures for routine freshwater monitoring. In order to study and overcome these drawbacks, we constructed four de novo indices to assess river ecological status based on the same biological samples of diatoms analysed with morphological and molecular methods. The biological inventories produced are (i) morphospecies identified by microscopy, (ii) OTUs provided via metabarcoding and hierarchical clustering of sequences using a 95% similarity threshold, (iii) individual sequence units (ISUs) via metabarcoding and only minimal bioinformatical quality filtering and (iv) exact sequence variants (ESVs) using DADA2 denoising algorithm. The indices based on molecular data operated directly with ecological values estimated for OTUs/ ISUs/ ESVs. Our study used an approach of bypassing taxonomic assignment, so bias related to unclassified sequences missing from reference libraries could be handled and no information on ecology of sequences is lost. Additionally, we showed that the indices based on ISUs and ESVs were equivalent, outperforming the OTU-based one in terms of predictive power and accuracy by revealing the hidden ecological information of sequences that are otherwise clustered in the same OTU (intra-species/intra-population variability). Furthermore, ISUs, ESVs and morphospecies indices provided similar estimation of site ecological status, validating that ISUs with limited bioinformatics treatments may be used for DNA freshwater monitoring. Our study is a proof of concept where a taxonomy- and clustering-free approach is presented, that we believe is a step forward to a standardised and comparable DNA bioassessment, complementary to morphological methods. How type material revision can influence biomonitoring analysis: a case study of Fragilaria capucina Bart Van de Vijver1,2, Adrienne Mertens3, Carlos E. Wetzel4, Luc Ector4 1Meise Botanic Garden, Research Department, Nieuwelaan 38, Meise 1860, Belgium 2University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1 B-2610 Wilrijk, Belgium 3Diatomella, IJkelaarstraat 3, Overasselt 6611 KN, Netherlands 4Luxembourg Institute of Science and Technology (LIST) Environmental Research & Innovation (ERIN) Department, 41 Rue du Brill Belvaux 4422, Luxembourg The complex of species around Fragilaria capucina Desmazières and the multiple varieties and subspecies that have been described in the past 150 years, is one of the groups that is the most difficult to identify. Species drift, the continuous broadening of the morphological species description, and seemingly simplified diatom analysis in routine biomonitoring resulted also in a profound flattening out of ecological interpretations. Krammer & Lange-Bertalot (2004) and later Lange-Bertalot et al. (2017) reduced in their monographs the actual number of Fragilaria taxa in European rivers and lakes to a strict minimum lumping that way several individual taxa and thus creating broader ecological amplitudes for several taxa. Type revision of several taxa described by Grunow, Kützing and Østrup led to a better morphological understanding of these taxa. Examples are Fragilaria gracilis Østrup, F. vaucheriae (Kützing) J.B.Petersen and F. rumpens (Kützing) G.W.F.Carlson (Tuji 2007, Tuji & Williams 2006, 2008, 2013, Wetzel & Ector 2015). These revisions are usually limited to the morphological aspects of the taxa, not taking into account possible ecological data that can be derived from the diatom community present in the type slide. During this presentation the morphological and ecological revision of the type material of Fragilaria gracilis and Fragilaria rumpens will be presented. Observations of both species from Flemish and Swedish rivers will be compared and discussed in the light of water quality monitoring. References Krammer, K. & Lange-Bertalot, H. 2004. Bacillariophyceae 3. Teil. Centrales, Fragilariaceae, Eunotiaceae. In: Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (eds), Süßwasserflora von Mitteleuropa Band 2/3. Sprektrum Akademischer Verlag, Heibelberg - Berlin. 598 pp.
Lange-Bertalot, H., Hofmann, G., Werum, M. & Cantonati, M. 2017. Freshwater benthic diatoms of Central Europe: Over 800 common species used in ecological assessment. English edition with updated taxonomy and added species. Koeltz Botanical Books, Schmitten- Oberreifenberg. 942 pp.
Tuji, A. 2007. Type examination of Fragiaria gracilis Østrup (Bacillariophyceae). Bulletin of the National Museum of Nature and Science, Series B (Botany), Tokyo 33(1): 9-12. Tuji, A. & Williams, D.M. 2006. Typification of Conferva pectinalis O. F. Müll. (Bacillariophyceae) and the identity of the type of an alleged synonym, Fragilaria capucina Desm. Taxon 55 (1): 193-199. https://dx.doi.org/10.2307/25065541
Tuji, A. & Williams, D.M. 2008. Typification and type examination of Synedra familiaris Kütz. and related taxa. Diatom 24: 25-29. https://doi.org/10.11464/diatom1985.24.0_25
Tuji, A. & Williams, D.M. 2013. Examination of types in the Fragilaria vaucheriae-intermedia species complex. Bulletin of the National Museum of Nature and Science, Series B (Botany), Tokyo 39 (1): 1-9. Wetzel, C.E. & Ector, L. 2015. Taxonomy and ecology of Fragilaria microvaucheriae sp. nov. and comparison with the type materials of F. uliginosa and F. vaucheriae. Cryptogamie, Algologie 36 (3), 271-289.
A decade of lake and stream diatom sampling: temporal trends and land use impacts Annika Vilmi, Satu Maaria Karjalainen, Jukka Aroviita Finnish Environment Institute SYKE, Paavo Havaksen tie 3, 90570 Oulu, Finland In Finland, there is a nationwide monitoring program for the impacts of agriculture and forestry. The aim of this program, which started in 2007, is to enhance understanding of long- term changes in aquatic communities and provide nationwide information of the status and trends in freshwater systems impacted by diffuse pollution (e.g. nutrients, suspended solids). The program covers approximately 60 rivers and 50 lakes, half of them sampled annually for various biological groups, including benthic diatoms, and water quality. Now, the first analyses of the decade-long monitoring dataset are ready. Among the sampled organism groups, diatom- based status indices were the most sensitive to land use impacts and associated diffuse pollution. In this presentation, we show how the status indices vary in space and time, and relate their variation to water physico-chemical features and land use of the surrounding catchments. We also point out some interesting diatom species which have specific indicator value. The information gathered during a decade of monitoring offers important insights on temporal and spatial developments of diatom communities, ecological status and aquatic ecosystems in general.
Diatom Biogeography: Is there a point to it?
David Williams
The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
Part of the text for this meeting has the following: “For the last three decades, diatom systematists have been documenting the extent of diatom endemism, a topic previously thought to be of little significance”. Its significance – or, maybe, its insignificance – was primarily seen as a component of assessing various diatom floras from around the world and describing what they were composed of in terms of their species diversity. But it become obvious to me quite early on that diatom endemism had been neglected simply by looking through some non- European floras, engaging with the published images, then checking the names – for me, it was Frenguelli’s Contribuciones para la sinopsis de las Diatomeas Argentinas (in Boletín de la Academia Nacional de Ciencias en Córdoba 27, 13-119, 1923), even though there were over 50 new names and combinations. It was clear what was happening: In many cases, European names were being used for a wide variety of specimens. I didn’t write anything substantial on biogeography until 1995, something based on a paper presented at the 13th International Diatom Symposium (Williams, DM. 1995. Diatom Biogeography: Some preliminary considerations. Proceedings of the 13th International Diatom Symposium, BioPress Ltd, pp. 311-319). Here I partly focused on a review piece written by Rick Battarbee and Don Charles, published in 1987 (Battarbee, R.W. & Charles, D.F. The use of diatom assemblages in lake sediments […] Progress in Physical Geography, 11, 552—580, 1987). Although that paper was addressing issues topical then (and maybe still) concerning diatom distributions one passage from the discussion captured my attention: “[These studies] help to explain why some sites fail to produce expected diatom assemblages for a given pH, and why certain taxa have regionally discontinuous distributions”. Those two aspects – expected diatom assemblages and regionally discontinuous distributions – were considered by Battarbee and Charles in terms of their ecological requirements rather than any historical factors. Almost as if diatom ecologists need not – and would not – consider evolutionary factors when dealing with present day diatom distributions. The other part of my presentation was work I had doing over a long period of time with the genus Tetracyclus (Williams, DM. 2004. On diatom endemism and biogeography: Tetracyclus and Lake Baikal Endemic Species. Proceedings of the 17th International Diatom Symposium, BioPress Ltd, pp. 433-459). It was evident to me then, and it still is, that an as yet unexplainable historical aspect was emerging. In this presentation I intend to re-visit some of these issues, look at some further evidence, and offer a framework for understanding, or at least studying, diatom biogeography so that the point of the exercise can be appreciated.
Poster presentations
Cymbella
Identification of Cyclostephanos species using molecular and morphological methods Malin Alf, Thomas Hübener, Konrad Schultz, Mirko Dressler Department of Botany, University of Rostock, Wismarsche Straße 44/45 Rostock 18057, Germany Cyclostephanos is a genus of centric diatoms, which can be found in various freshwater habitats. In many cases, species delimitation based on morphological characters can be challenging, especially in the light microscope. In those cases, DNA-barcoding can be a useful supportive tool. In this study 16 monoclonal cultures from six different countries were studied morphologically and molecularly to identify different species and relate those in a preliminary phylogeny of the genus. For the molecular analyses four different genetic markers (18S, LSU, rbcL, cox1) were sequenced and compared. The morphology was studied using SEM images. The genetic analyses showed five different clusters, which correspond to the overall morphological characterizations. Some of them could clearly be assigned to certain taxa, however, for some of the clusters the identification was not possible. Moreover, the aim of this study was to connect the different morpho-species to barcoding sequences, in order to provide references for future meta-barcoding projects.
Modern and fossil diatom flora of Tunisia Leila Ben Khelifa1, Zaara Ben Mosbah C.2, Hajji I.2 15 rue André Danjon, Paris 75019, France 2University El Manar, LRME, Tunis 2092, Tunisia Tunisia, in the western Mediterranean, has about 1200 km coastline, including the shores of coastal lagoons, which represent around 2.5% of the total coastline of the Mediterranean (Aleya et al., 2019). Besides the convergence of African and Eurasian plates generated extensional coastal structures (Chihi, 2003), thus continental-marine margin is very sensitive since the Neogene and Quaternary sequences are under revision. In addition, intensive urbanization and anthropogenic activities damage the Tunisian coast; therefore, several Tunisian wetlands are RAMSAR sites and were subject to diverse study on pollution and diatoms are used to distinguish either anthropogenic effect and/or climatic change in Quaternary sediments (Zaara & al., 2019). In total, more than 600 species were recorded from all the country in particular, from coastal lagoons, hydrothermal springs and from the unique permanent river, Majerda and tributaries (Ben Khelifa, 1989). Diatom assemblage and diversity depend on the associate geochemistry linking with the regional geology. A hundred of sites were sampled in 1984, 1985 and 1986. The majority were not polluted and their microfloristic content therefore constitutes a reference. For instance, Ouchir & al., 2017, showed the effect of metal contamination in lake Ichkeul using diatoms and assigned to Achnanthidium minutissimum (Kütz.) Czarnecki a Fe tolerance. In Ben Khelifa, 1989, Achnanthes minutissima Kütz. prefer salinity of 0.5 g/l and a calcium sulphate facies rich in Ca2+. It was dominant at 80% in an iron-free water. So, to update taxonomy and to use this species as bioindicator, further SEM analyses is needed mainly when we might be dealing with a new species (Van de Vijver, personal comm.). Other authors pointed out the presence of the harmful specie Pseudonitzschia in aquaculture. Daly Yahia- Kéfi et al., 2005, used a specific preference index between species, temperature, salinity and major nutrients in the bay of Tunis and Drira &al., 2014, state that the biomass was a better bio-indicator than abundance. In 2019, new sampling missions in Majerda and in the lake of Tunis gives an image of site restoration cases. In particular, the harmful Pseudonitzschia is not observed in the North lake of Tunis but highly tolerant small Navicula are abundant in polluted area, and no teratological forms were observed. Quaternary diatoms, in Tunisia, are recorded from three sites: Tunis Lagoon, gulf of Gabès and the Chott region. Because of high alkalinity, fossil diatom dissolve rapidly. Only in Holocene sequences, we can observe beautiful assemblage in particular inside the Cerastoderma lenses of Akarit. In Lac of Tunis, however it is difficult to distinguish climatic event change from anthropogenic influence in the upper Holocene but we distinguish a high productivity event with big Nitzschia as Nitzschia cf. longissima (Bréb.) Grun. at the depth -52m corresponding to isotopic stage7 (Zaara Ben Mosbah &al.,2017). An enigmatic form less than 8 µm, is abundant at some levels, it might correspond either to Phytolith or to Minidiscus; an SEM is necessary to state if we have allochtonous eolian transport or if we have a transgressive event. Fossil sequences, in the Chott area and Akarit region are rich with Denticula elegans var. africana that was first described by Hustedt in the oasis of Gafsa and diatom assemblage reflect a far lower salinity than in the Gulf of Tunis. Aleya L. et al. 2019. Tunisia in World Seas: An Environmental Evaluation. Vol.1, 261-282. Ben Khelifa L. 1989. Diatomées continentales et paléo milieux du Sud-Tunisien (PALHYDAF site1) au Quaternaire supérieur : approche statistique basée sur les diatomées et les milieux actuels. Paris. http://www.theses.fr/1989PA112407 Chihi L. 2003. Place de la Tunisie dans l’évolution géodynamique de la Méditerranée occidentale du Néogène à l’actuel. ATEIG-Chronologie des évènements tectoniques en Tunisie. Daly Yahia-Kéfi et al. 2005. Spatio-temporal distribution of the dominant Diatom and Dinoflagellate species in the Bay of Tunis (SW Mediterranean Sea). Mediterranean Marine Science. Vol.6(1), 17-34. Drira Z. et al. 2014. Seasonal changes on planktonic diatom communities along an inshore- offshore gradient in the gulf of Gabes (Tunisia). Acta Ecologica Sinica 34, 34-43. Ouchir et al., 2017. Periphytic diatom communities in tributaries around Lake Ichkeul, northern Tunisia: a preliminary assessment. African Journal of Aquatic Science, 42(1), 65-73. Zaara Ben Mosbah, C. et al., 2017. évolution Paléo-environnementale et quaternaire de la Lagune de Tunis (golfe de Tunis, Tunisie). Quaternaire, 28(4), 491-503. Zaara Ben Mosbah, C. Hajji I. & Ben Khelifa L. 2019. Evolution actuelle et quaternaire du Lac de Tunis, Tunisie septentrionale. 38ème colloque de l’association des Diatomistes de Langue Française (ADLaF). Metz. Résumé.
Epiphytic diatom community shows larger response to bryophyte and lichen vegetation type than nutrient and water additions within Windmill Islands, East Antarctica Jordan Bishop1, Jane Wasley2,3, Melinda Waterman2, Tyler J. Kohler4 Bart Van de Vijver5,6, Sharon Robinson1,7, Kateřina Kopalová1,8 1Department of Ecology, Charles University, Prague, Czech Republic 2Centre for Sustainable Ecosystem Solutions, University of Wollongong Wollongong, Australia 3Antarctic Conservation and Management Program, Australian Antarctic Division Kingston, Australia 4Stream Biofilm and Ecosystem Research Laboratory École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 5Meise Botanic Garden, Research Department, Nieuwelaan 38, Meise 1860, Belgium 6University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1 B-2610 Wilrijk, Antwerpen, Belgium 7Global Challenges Program, University of Wollongong, Wollongong, Australia 8Section of Plant Ecology, Academy of Sciences of the Czech Republic Třeboň, Czech Republic Continental Antarctica is a cold polar desert sparsely pocketed with ice-free areas. Notably, the Windmill Islands feature extensive, well-studied bryophyte and lichen vegetation stands. Despite a well-known association between mosses and epiphytic diatoms (Bacillariophyceae), environmental factors controlling diatom community structure are poorly understood. The present poster illustrates the results of a study analysing the association of epiphytic diatoms on two bryophyte (healthy and moribund) and two lichen vegetation types (crustose and Usnea), investigated using a field manipulation experiment altering nutrient and water content along a gradient based on projected availability due to climate change. Diatom communities were characterized, and community differences were examined based on redundancy analyses (RDA) and permutational analysis of variance (PERMANOVA). Furthermore, diversity indices were calculated and differences in treatments and vegetation types tested with ANOVA. Bryophyte and lichen vegetation types significantly differed in their epiphytic diatom composition, whereas nutrient treatments and their combined effects did not. Specifically, diatom species richness, Shannon diversity and evenness showed significant differences within pairwise comparisons of all four community types. Our findings suggest that despite increased nutrient and water availability, diatom community structure is determined by the underlying vegetation type and as a result, changes in their abundance and coverage with projected climate change are likely to impact regional diatom communities.
Soil diatom communities of Ile Amsterdam (TAAF, South Indian Ocean) Tereza Cahová1, Barbora Chattová1, Bart Van de Vijver2,3 1Department of Botany & Zoology, Faculty of Science, Masaryk University, Kotlarska 2 61137 Brno, Czech Republic 2Meise Botanic Garden, Research Department, Nieuwelaan 38, B-1860 Meise, Belgium 3University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1 B-2610 Wilrijk, Belgium Diatoms are widespread single-celled algae with an essential role in global primary productivity. Terrestrial diatoms play a crucial role in the soil microbial community as a carbon source, pioneer organisms, or soil particles aggregators thanks to their mucilage production. They also belong to the most diverse groups of organisms in the sub-Antarctic region. The sub- Antarctic region is composed of small and isolated islands set in the vastness and harsh conditions of the Southern Ocean. In the warmth part of the sub-Antarctica, Ile Amsterdam (77°30’E, 37°50’S) is one of the world’s most remote islands. It is a small geologically young volcanic dome, rising to 881 metres, surrounded with steep cliffs. Due to this geomorphology, permanent water bodies are restricted only to the caldera and running water is almost absent on the island, only with several exceptions on the southern side of the island. The island’s climate differs depending on the altitude. It ranges from the temperate climate at the lower altitudes to almost sub-Antarctic at the top of the island. This study shows the last piece of Ile Amsterdam’s diatomological research. Previous studies were focused on freshwater and moss- inhabiting diatoms, while this research brings information about the composition of soil diatom communities. The analysis of 76 soil samples revealed 128 diatom species (and additional 17 outside counting) mostly with restricted biogeographical ranges. Following NMDS analysis divided all samples into five groups with three samples standing solitarily. Indicator species were identified for each of these groups. These analyses indicate that the soil diatom flora is as unique as freshwater and moss-inhabiting floras of Ile Amsterdam and it seems that moisture availability, specific conductance and pH belong to the major factors determing the species composition of each community.
Diatom Collections at the Natural History Museum: Using digitisation to maximise research potential Edgley César, Jo Wilbraham, David Williams The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom The Diatom Collection at the Natural History Museum (BM) contains a wealth of material assembled over 200 years with new specimens continually being added. With an estimated 300,000 items it is rich in nomenclatural type specimens and historically significant exsiccatae sets making it one of the largest and most important collections of its kind in the world. The collection includes samples from freshwater, marine and brackish environments from across the world with all major diatom groups represented in extant and fossil material. Although the bulk of the collection is comprised of glass microscope slide preparations there are also extensive correlated raw and cleaned samples in bottles, strewn specimens on glass, mica and paper as well as diatomite. Accessing a particular specimen in the main glass slide collection of over 100,000 objects is possible through a card index of species names, each with a roll call of slide numbers for the relevant taxon. This card index comprises c.12000 taxon cards and contains more than 200,000 species references. This system is sufficient to find an example of a particular species in the collection but for modern research the data on these cards require electronic capture in order to facilitate curation and maximise the collection’s potential. A good percentage of the specimens in the collection have never been examined since its acquisition and this represents a vast untapped resource for research into comparative biology, environmental change and, in some cases, ecological time series studies. We have started a project to image and transcribe this card index into a digital format which will provide a base for further digitisation work and a new way to query our collection. The imaging and transcription work has been completed and the analysis of the cards transcribed has revealed a 10% increase in the number of nomenclatural type specimens recorded in the collection as well as highlighted several possibly undescribed new species and potential research projects. The list of names compiled will ultimately be associated with each microscope slide in the main collection, creating a digital framework of records in the Museum’s collections management system, greatly improving curation and broadening access to external users via the Museum’s data portal.
Ecohydrological characterization of terrestrial diatoms Jasper Foets1, Carlos E. Wetzel1, Adriaan J. Teuling2, Laurent Pfister1
1Luxembourg Institute of Science and Technology, 41 Rue de Brill Belvaux 4422, Luxembourg 2Wageningen University & Research, Droevendaalsesteeg 4 Wageningen 6708 PB, Netherlands In the past decade, terrestrial diatoms (i.e. diatoms living on soils) have been studied for tracing water sources and pathways across a wide range of spatial scales. Despite encouraging results, the innovative tracer concept has reached its limits due to the lack of ecological knowledge on terrestrial diatoms and restrictions proper to the sampling locations. To overcome the former, the spatial and temporal variability of diatom communities and their absolute abundances on soils were investigated and the occurrences of common soil diatoms were tested to an extensive set of environmental variables. Also, in order to reduce the number of samples, the Phillips sampler, a time-integrated mass-flux sampler, was explored for sampling drift diatom communities in streams during three rainfall-runoff events. The results of this research allow to reduce the sampling effort and speed up the analysis of diatom-based hydrological tracer studies. They also indicate that many more diatoms can be used as environmental markers in hydrological tracing, that more locations can be sampled, and that the number of stream sampling sites can be increased in the future. The work thus improved the use of terrestrial diatoms as hydrological tracers.
Molecular and morphometric analyses of the Cyclotella meneghiniana species complex Josephine Franke, Thomas Hübener, Konrad Schultz, Mirko Dressler Department of Botany, University of Rostock, Wismarsche Straße 44/45 Rostock 18057, Germany Cyclotella meneghiniana Kützing is one of the most common centric freshwater diatoms and can be found in various habitats. The morphology of its frustule is quite variable making taxonomic delimitation and determination problematic. Studies by Beszteri et al. (2005, 2007) have shown a high molecular variability. Different genetic groups have been found. In this study SEM pictures of 16 monoclonal cultures from seven different countries were analysed and compared confirming a variable morphology. However, none of the groups could be separated by the nine selected morphometric parameters. The sequences of three DNA- barcoding markers (LSU D2/D3, 18S, rbcL) were analysed and compared in order to assess the genetic variability of C. meneghiniana. As a result, a high genetic variability was found. The most variable marker was LSU D2/D3. Genetic variants of this marker within C. meneghiniana were arranged into six groups and named using the nomenclature established by Beszteri et al. (2005, 2007). One of these groups has not been described before. Moreover, a statistical analysis showed no correlation between the geographical location and the genetic groups.
Moss-inhabiting diatoms from Campbell Island (sub-Antarctic Region) Charlotte Goeyers1,2, Bart Van de Vijver1,2 1Meise Botanic Garden, Research Department, Nieuwelaan 38, Meise 1860, Belgium 2University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1 B-2610 Wilrijk, Antwerpen, Belgium Diatoms (Bacillariophyta) are one of the most abundant algal groups in Polar ecosystems, both in number of specimens as in number of species. Due to their characteristic frustules and their significant responses to changes in their physical and chemical environment, they are excellent bio-indicators and are used in applied environmental, biogeographical and paleo-ecological studies. Especially in Polar regions, diatoms proved to be useful indicators of environmental and climatic changes. Contrary to the 20th century view, Polar diatom floras show a high degree of bioregionalism, together with a high endemicity. However, due to force-fitting practices, outdated species taxonomy and incorrect identifications, a revision of the Polar diatom flora is required for their conservation and further use as bio-indicators. This master thesis considers the diatom flora found in a historic moss collection, sampled on Campbell Island (sub-Antarctic) in 1969-1970 by Prof. Dr Dale Vitt. In total, 66 moss samples were retrieved from the British Antarctic Survey (BAS) herbarium in Cambridge, United Kingdom. This historic moss collection was compared with collections of samples from other sub- Antarctic islands. Analysis of the Campbell Island diatom flora showed a well-developed and species-rich diatom composition. During the survey, a large number of currently unknown diatom species were observed that could not be identified using the available literature. Detailed analysis of light and scanning electron microscopy observations and comparisons with similar taxa worldwide led to the description of several new species. The revision of the diatom flora of Campbell Island will contribute to a better understanding of Polar diatom biodiversity.
Diatoms thrive in areas where seawater has naturally high levels of carbon dioxide Jason Hall-Spencer1,2, Ben Harvey2, Shigeki Wada2, Sylvain Agostini2 and collaborators 1School of Biological and Marine Sciences, Universities of Plymouth Plymouth PL4 8AA, United Kingdom 2Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda Shizuoka 415-0025, Japan Diatoms are so important in ocean food-webs that any human induced changes in their abundance could have major effects on the ecology of our seas. Large diatoms, such as Biddulphia biddulphiana, greatly increase in abundance at marine carbon dioxide seeps in both the Pacific and the Mediterranean basins. Seawater CO2 enrichment stimulates the growth and photosynthetic efficiency of these benthic diatoms. Our observations suggest that ocean acidification will shift photic zone community composition so that coastal food-web structure and ecosystem function are simplified and more strongly affected by seasonal algal blooms.
Climate change in Bavarian mountain lakes – differential diatom responses among different lakes Wolfgang Küfner, Andrea Hofmann, Stefan Ossyssek, Jürgen Geist, Uta Raeder Chair of Aquatic Systems Biology, Department of Ecology and Ecosystem Management Limnological Field Station Iffeldorf, Hofmark 1-3, Iffeldorf, Bavaria 82393, Germany Mountain lake ecosystems are adapted to harsh alpine conditions like low nutrient availability, cool temperatures, high radiation and a short vegetation period. This strong adaptation makes them particularly vulnerable to global change. However, not every mountain lake is likely to react in the same way as every lake is unique. Accordingly, different lakes with a wide range in altitude, depth and surface as well as different geologies were examined for their response to climate warming. Subfossil diatom analyses from 210Pb and 137Cs-dated sediment cores from 23 lakes in the Bavarian and Tyrolean calcareous Northern Alps served as basis for the study. PCA, DCA and regression analyses revealed five different developments of diatom assemblages, which are mainly affected by lake depth, altitude and geology. The deeper and lower the mountain lakes are, the earlier planktic species appear and more often dominate the subfossil diatom assemblages, in particular Cyclotella species. In contrast, the shallower the lakes are, the higher is the reorganization of the diatom community (beta diversity). In montane and subalpine shallow lakes, Achnanthidium species – usually accompanied by epiphytic species of the genera Navicula and Encyonopsis – replace a Staurosira-dominated assemblage. In contrast, alpine shallow lakes lacking epiphytic habitats are still not subject to any directional diatom shift and are dominated by species of the Staurosira complex. Corresponding to changes in diatoms, macrophytes, which determine a shift in diatom assemblages, rise in altitude and currently present up to 1600 m, as well as split the two shallow lake types. Furthermore, lake geology plays an important role as it defines the stability of the water level and limnology of a lake. In shallow lakes with large water level fluctuations, the desiccation tolerant Denticula tenuis replaces the Staurosira dominated assemblages, whereas in one studied doline lake Diploneis species substitute Nitzschia denticula and the proportion of planktic species is very small despite its great depth. Possibly, other species are dominating in doline lakes due to cool ground water constituting the entire water supply and inhibiting stratification throughout the year. In mountain lakes with direct anthropogenic influence, enhanced nutrient supply disguise climate change response and can feign inverse trends. Referring to these subfossil diatom analyses, climate change impact can be classified, quantified and qualified in a variety of mountain lakes with the aim to predict their future development and vulnerability. The study is funded by the Bavarian State Ministry of the Environment and Consumer Protection.
Benthic diatoms in small Estonian lakes – two substratum type comparsion Maili Lehtpuu, Sirje Vilbaste Estonian University of Life Sciences, Fr.R.Kreutzwaldi 1, Tartu, Tartu county 51006, Estonia The aim of the current study was to compare benthic diatom communities of the two most common substratum types (cobbles and macrophytes) in small Estonian lakes and analyse how results impact lake ecological status calculations, carried out according to the Water Framework Directive. The main hypotheses of this study were: 1) Macrophytes can affect final ecological status evaluation results, depending on the type of the lake – in more eutrophic conditions impact of the substratum is lower. 2) Samples collected from macrophytes are generally showing better ecological status values than samples collected from cobbles. To study benthic diatom communities, samples were collected from 12 small lakes where both cobbles and macrophytes were present. Sampled lakes were distributed all over Estonia and covered broad amplitudes of hydrochemical parameters (i.e. nutrients, pH, alkalinity), that are considered as important factors for benthic diatom community development. The composition of diatom communities, the number of species and three species diversity indexes (Pielou index, Shannon’s index and Simpson’s index) were used to compare benthic diatom communities on macrophytes and on cobbles. To reveal relationships between diatom communities and hydrochemical characteristics of studied lakes, correlation analysis was used. Small lakes ecological status calculations according to benthic diatoms from cobbles and macrophytes showed slight differences. Samples collected from macrophytes showed slightly higher ecological status class then samples collected from cobbles. Comparing benthic diatom species communities on macrophytes and cobbles, the number of species was in general higher in cobbles samples, but fluctuated more in macrophyte samples. The most common species (≥10% of all counted valves) or dominant species (≥25% of all counted valves) in almost all samples was Achnanthidium minutissimum s.l., it was found in 11 studied lakes. Species diversity indexes on macrophyte and cobble communities were slightly different, but all three indexes calculated – Pielou, Shannon’s and Simpson’s – were higher on cobbles. Benthic diatom indexes, calculated from samples collected from cobbles, showed significantly important (p≥ 0.05) correlations with hydrochemistry parameters, but no significant correlations were found for macrophytes samples. Our study confirmed both proposed hypotheses. In lakes, where more oligotrophic conditions were present, samples from macrophytes showed better results than samples from cobbles and minor differences were in lakes, where conditions were more meso- to eutrophic. Species composition and numbers also confirmed our hypotheses. The number of species was higher and more stable in cobble samples, regardless of lake type and hydrochemical conditions.
Benthic diatom communities in urban streams and the role of riparian buffers Petra Thea Mutinova1, Maria Kahlert2, Benjamin Kupilas1, Brendan G. McKie2 Nikolai Friberg1,3,4, Francis J. Burdon2 1Norwegian Institute for Water Research (NIVA), Gaustadallèen 21, NO-0349 Oslo, Norway 2Department of Aquatic Sciences and Assessment Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden 3Freshwater Biological Section, Department of Biology, University of Copenhagen 2100 Copenhagen, Denmark 4Water@leeds and School of Geography, University of Leeds Leeds LS2 9JT, United Kingdom Urbanization impacts stream ecosystems globally through degraded water quality, altered hydrology, and landscape disturbances at the catchment and riparian scales, causing biodiversity losses and altered system functioning. Addressing the “urban stream syndrome” requires multiple mitigation tools, and rehabilitation of riparian vegetation may help improve stream ecological status and provide key ecosystem services. However, the extent to which forested riparian buffers can help support stream biodiversity in the face of numerous environmental contingencies remains uncertain. We assessed how a key indicator of stream ecological status, benthic diatoms, respond to riparian habitat conditions using 10 site pairs (each comprising of one unbuffered and one buffered reach), and additional upstream and downstream sites in the urbanized Oslo Fjord basin. Diatom communities were structured by multiple drivers including spatial location, land use, water quality, and instream habitat. Among these, riparian habitat independently explained 16% of variation in community composition among site pairs. Changes in community structure and indicator taxa, along with a reduction in pollution-tolerant diatoms in the presence of forested riparian buffers, suggested tangible benefits for stream biodiversity in urban environments. Managing urban impacts requires multiple solutions, with forested riparian zones providing a potential tool to help improve biodiversity and ecosystem services.
Assessment of biological quality along a metal pollution gradient applying macroinvertebrates and diatoms Stijn Van de Vondel1,2,3, Lieven Bervoets3, Bart Van de Vijver1,2 1Meise Botanic Garden, Research Department, Nieuwelaan 38, Meise 1860, Belgium 2University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1 B-2610 Wilrijk, Belgium 3University of Antwerp, Department of Biology, SPHERE, Groenenborgerlaan 177 B-2020 Antwerp, Belgium The European Water Framework Directive was created to monitor and establish the quality of all waterbodies within the European Union urging all member states to perform water quality assessment based on biological, physicochemical and hydro-morphological elements. Among others, diatoms and macroinvertebrates have been shown to form very reliable bio-indicators for general water quality monitoring. The present study evaluates the impact of a metal pollution gradient caused by historical contamination in a Flemish lowland river. It follows previous research from 2006-2007 that evaluated the water quality of the Dommel using diatoms and macroinvertebrates. Indices based on these bio-indicators are applied to monitor the water quality of six sampling localities of the river during three campaigns. A physicochemical analysis of water, sediment and a selection of macroinvertebrates was carried out to investigate the presence of metals. Our results suggest that sites downstream of the Eindergatloop – a tributary of the Dommel – were different from upstream waters in terms of physicochemistry, showing increased levels of electrical conductivity, sulphate and chloride. Metal contents in water and sediment showed elevated levels of cadmium and lead in downstream sites, while water samples showed higher concentrations for copper, zinc and arsenic. Differences between sampling campaigns were observed for some of these physicochemical variables. Metal concentrations in macroinvertebrates displayed increased levels of zinc, arsenic, cadmium and lead downstream of the Eindergatloop, while diatoms did not show a clear sign of metal-induced deformities. Biotic diatom indices (IPS, IBD) indicated lower biological quality of downstream sites, while the Multimetric Macroinvertebrate Index Flanders (MMIF) did not show any differences. Community analysis indicated increasing downstream levels of pollution, confirming earlier observations. All in all, the Dommel’s water quality has improved compared to 2006, but has not yet achieved the WFD goal of being of ‘good ecological quality’.
Nitzschia species from inland saline waters in the Vojvodina Province (Serbia) Danijela Vidaković1, Jelena Krizmanić2, Luc Ector3, Carlos Wetzel3 Bojan Gavrilović4, Miloš Ćirić1 1University of Belgrade, Institute of Chemistry, Technology and Metallurgy National Institute of the Republic of Serbia, Njegoševa 12 Belgrade 11000, Republic of Serbia 2University of Belgrade, Faculty of Biology Institute of Botany and Botanical Garden “Jevremovac”, Takovska 43 Belgrade 11000, Republic of Serbia 3Luxembourg Institute of Science and Technology (LIST) Environmental Research & Innovation (ERIN) Department, 41 rue du Brill Belvaux 4422 Luxembourg 4Serbian Academy of Sciences and Arts, Geographical Institute “Jovan Cvijić” Department of Physical Geography, Djure Jakšića 9, Belgrade 11000, Republic of Serbia Saline habitats, such as lakes, ponds and channels in the Vojvodina Province (Serbia) are alkaline and unique due to their specific physical and chemical features. During three years (2017-2019) we investigated 10 different saline lakes, ponds and channels in the Serbian part of the Carpathian Basin. By far the most abundant genus was Nitzschia Hassall with 27 recorded taxa. Some of them are characteristic for electrolyte rich waters, e.g. N. frustulum, N. palea, N. inconspicua, N. supralitorea. However, we found species specific for marine and brackish waters, e.g. N. communis, N. thermaloides, N. reversa. Of all recorded Nitzschia species four taxa could not be identified to species level. One of them with sigmoid outline, Nitzschia sp. 2, is very similar to N. austriaca but differs in striae density and distribution of fibulae. In Nitzschia sp. 2 transapical striae are not visible in LM. In addition, in both species fibulae are quite regularly distributed along the raphe canal, but in N. austriaca the central fibulae are more widely spaced than in the other species. In Lake Bela bara we found both species with abundance of 94.93% for Nitzschia sp. 2. and 1.21% for N. austriaca. The poster illustrates the Nitzschia diversity in inland saline waters in Vojvodina Province, with an emphasis on sigmoid Nitzschia species that might be new to science.