1. Microalgal communities in mucilage aggregates (Northern Adriatic Sea, summer 2024) based on microscopy and metabarcodingMarika Ubaldi, Francesca Neri, Giorgia Montali, Tiziana Romagnoli, Aurora Tomasini, Federica Cerino, Timotej Turk Dermastia, Patricija Mozetič, Janja Francé, Camilla Spoto, Stefano Accoroni, Cecilia Totti, 2026, original scientific article Abstract: The mucilage phenomenon consists of the appearance of large gelatinous aggregates floating in the water column. In summer 2024, this event has reappeared in the Northern Adriatic Sea (NAS) on a large scale. This study provides an integrated characterization of the microalgal community within mucilage aggregates and surrounding waters in two NAS areas (Gulf of Trieste and Conero Riviera) using light microscopy (LM), metabarcoding (MB) based on ribosomal 18S V4 and V9 markers, and scanning electron microscopy (SEM) for selected taxa identification. Mucilage aggregates acted as dynamic microbial hotspots, hosting a rich diatom community, with abundances 1–2 orders of magnitude higher than in the surrounding water. Dominant diatom species were Cylindrotheca closterium, Nitzschia spp., Nitzschia gobbii, and Thalassionema nitzschioides. Some phytoflagellates (e.g., Tetraselmis spp.) and dinoflagellates (e.g., Karlodinium veneficum, Pseliodinium fusus, and Wangodinium sinense) were detected exclusively by MB, while LM and SEM revealed species missed by other approaches. Gonyaulax fragilis, one of the species indicated as an important mucus producer, was present at the onset and throughout the phenomenon, as detected by LM and MB. The integrated approach improves knowledge of microalgal communities in NAS mucilage.
Keywords: mucilage, Northern Adriatic Sea, phytoplankton, microalgae, metabarcoding, microscopy, Gonyaulax fragilis, Harmful Algal Blooms
Published in DiRROS: 27.01.2026; Views: 546; Downloads: 449
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2. Unveiling microalgal diversity in Slovenian transitional waters (Adriatic Sea) : a first step toward ecological status assessmentPetra Slavinec, Janja Francé, Ana Fortič, Patricija Mozetič, 2026, original scientific article Abstract: This study presents the first comprehensive assessment of microalgal diversity in two Slovenian transitional waters (TWs): the shallow brackish lagoon of the Škocjanski Zatok Nature Reserve (SZNR) and the Rižana River estuary within the Port of Koper (PK) area. Between 2018 and 2021, water samples collected with a phytoplankton net were analyzed using light and scanning electron microscopy. In total, 240 species from 117 genera were identified in TW, dominated by diatoms and dinoflagellates, surpassing the diversity at a marine coastal station (91 species, 59 genera). Species richness was higher in PK (226) than in SZNR (154), mainly due to dinoflagellates and coccolithophores. Marine taxa predominated along the salinity gradient, with moderate contributions from brackish taxa and fewfreshwater forms, reflecting both natural and anthropogenic influences. Planktonic taxa dominated at all sites, while benthic forms were abundant in the lagoon, particularly in spring. Thirty-two taxa were recorded for the first time in Slovenian TW, mostly benthic or tychopelagic diatoms. The detection of Coolia monotis and five cyanobacterial genera with potentially harmful traits highlights the role of TW as an ecological interface. The taxonomic sufficiency analysis showed that the order level is sufficient to distinguish transitional from marine assemblages, beyond which ecological information is lost. Overall, this study highlights the importance of detailed taxonomic resolution for detecting microalgal diversity, including harmful and non-indigenous species to ensure robust ecological assessments under the WFD and MSFD directives.
Keywords: transitional waters, diversity, phytoplankton, harmful algal blooms, non-indigenous species, Adriatic Sea
Published in DiRROS: 27.01.2026; Views: 540; Downloads: 554
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