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Abstract: Phytoplankton plays a fundamental role in marine ecosystems and is widely used to assess environmental change. In this study, light microscopy and DNA metabarcoding approaches were used to investigate phytoplankton communities at three long-term monitoring sites in the northern Adriatic Sea. By combining the two approaches, more than 500 species were recorded. Metabarcoding detected substantially higher diversity, particularly among small and fragile organisms that are difficult to identify under a microscope, whereas microscopy was better for identifying larger species with distinctive morphology. Because species contain different amounts of genetic material, DNA data can overestimate or underestimate their true contribution to the community. Indeed, after applying correction factors that account for these differences, the DNA-based estimates became more consistent with the microscopy results for several phytoplankton groups. The differences among the samples were influenced more by the approach used than by the sampling location. Overall, combining these two approaches provides an accurate and robust picture of phytoplankton communities. In this way, it is possible to improve the reliability of marine biodiversity assessments and to support better environmental monitoring and management in coastal seas.
Keywords: phytoplankton, diversity, environmental DNA, Long-Term Ecological Research, amplicon sequencing, North Adriatic Sea
Published in DiRROS: 25.03.2026; Views: 289; Downloads: 220
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Abstract: Pseudo-nitzschia, a globally distributed diatom genus, dominates phytoplankton communities in biomass and abundance, with some species producing domoic acid (DA), the neurotoxin responsible for Amnesic Shellfish Poisoning (ASP). The Adriatic Sea has become a hub of Pseudo-nitzschia research over the past 15 years. This review synthesizes multidisciplinary research across Adriatic sub-basins, integrating morphological, genetic, and ecological data. While ASP has never been documented in the Adriatic, DA was occasionally detected in shellfish. The production was linked to toxic species such as P. multistriata, P. calliantha, and P. galaxiae, which were found to produce DA in cultures from Adriatic isolates. Despite progress, LM-based monitoring remains prevalent, underestimating species complexity and toxigenic potential. Electron microscopy and genetic barcoding have nonetheless revealed new insights into the species composition of this genus in Adriatic. A total of 14 species have been reported so far with prominent regional disparity: the northern and middle Adriatic host higher diversity, contrasting with the southern Adriatic, where only five species were confirmed, and research remains sparse. Seasonal dynamics show summer-autumn peaks in abundance, though interannual and regional variability is notable. We present recent advances from the Adriatic including the discovery of Pseudo-nitzschia-infecting viruses, population genomic insights in P. multistriata, and metabarcoding-driven revelations of cryptic diversity. Finally, we highlight critical knowledge gaps, including the ecological drivers of toxicity and the impacts of oligotrophication on community shifts. Collaborative, high-resolution methodologies (e.g., omics, automated imaging) are urged to address emerging challenges under climate change and anthropogenic pressures.
Keywords: Adriatic, Pseudo-nitzschia, diversity, ecology
Published in DiRROS: 14.04.2025; Views: 1144; Downloads: 583
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Abstract: Algal blooms impact trophic interactions, community structure and element fluxes. Despite playing an important role in the demise of phytoplankton blooms, only few viruses infecting diatoms have been cultured. Pseudo-nitzschia is a widespread diatom genus that commonly blooms in coastal waters and contains toxin-producing species. This study describes the characterization of a novel virus infecting the toxigenic species Pseudo-nitzschia galaxiae isolated from the northern Adriatic Sea. The ssRNA virus PnGalRNAV has 29.5 nm ± 1.2 nm icosahedral virions and a genome size of 8.8 kb. It belongs to the picorna-like Marnaviridae family and shows high specificity for P. galaxiae infecting two genetically and morphologically distinct strains. We found two genetically distinct types of this virus and screening of the global virome database revealed matching sequences from the Mediterranean region and China, suggesting its global distribution. Another virus of similar shape and size infecting Pseudo-nitzschia calliantha was found, but its genome could not be determined. In addition, we have obtained and characterized a new virus that infects Chaetoceros tenuissimus. The replicase protein of this virus is very similar to the previously described ChTenDNAV type-II virus, but it has a unique genome and infection pattern. Our study is an important contribution to the collective diatom virus culture collection and will allow further investigation into how these viruses control diatom bloom termination, carbon export and toxin release in the case of Pseudo-nitzschia.
Keywords: algal blooms, diatoms, virus, PnGalRNAV, genome, Adriatic Sea, marine virology, phytoplankton ecology, marine biology
Published in DiRROS: 23.10.2024; Views: 1462; Downloads: 1498
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Abstract: Research on marine microbial communities is growing, but studies are hard to compare because of variation in seawater sampling protocols. To help researchers in the inter-comparison of studies that use different seawater sampling methodologies, as well as to help them design future sampling campaigns, we developed the EuroMarine Open Science Exploration initiative (EMOSE). Within the EMOSE framework, we sampled thousands of liters of seawater from a single station in the NW Mediterranean Sea (Service d'Observation du Laboratoire Arago [SOLA], Banyuls-sur-Mer), during one single day. The resulting dataset includes multiple seawater processing approaches, encompassing different material-type kinds of filters (cartridge membrane and flat membrane), three different size fractionations (>0.22 µm, 0.22–3 µm, 3–20 µm and >20 µm), and a number of different seawater volumes ranging from 1 L up to 1000 L. We show that the volume of seawater that is filtered does not have a significant effect on prokaryotic and protist diversity, independently of the sequencing strategy. However, there was a clear difference in alpha and beta diversity between size fractions and between these and “whole water” (with no pre-fractionation). Overall, we recommend care when merging data from datasets that use filters of different pore size, but we consider that the type of filter and volume should not act as confounding variables for the tested sequencing strategies. To the best of our knowledge, this is the first time a publicly available dataset effectively allows for the clarification of the impact of marine microbiome methodological options across a wide range of protocols, including large-scale variations in sampled volume.
Keywords: marine microbiome, standardized sampling, inter-comparison, amplicon sequencing, microbial diversity, seawater sampling
Published in DiRROS: 12.07.2024; Views: 1466; Downloads: 1019
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Abstract: Pseudo-nitzschia H. Peragallo (1900) is a globally distributed genus of pennate diatoms that are important components of phytoplankton communities worldwide. Some members of the genus produce the neurotoxin domoic acid, so regular monitoring is in place. However, the identification of toxic members in routine samplings remains problematic. In this study, the diversity and seasonal occurrence of Pseudo-nitzschia species were investigated in the Gulf of Trieste, a shallow gulf in the northern Adriatic Sea. We used time series data from 2005 to 2018 to describe the seasonal and inter-annual occurrence of the genus in the area and its contribution to the phytoplankton community. On average, the genus accounted for about 15 % of total diatom abundance and peaked in spring and autumn, with occasional outbreaks during summer and large inter-annual fluctuations. Increased water temperature and decreased salinity positively affected the presence of some members of the genus, while strong effects could be masked by an unsuitable definition of the species complexes used for monitoring purposes. Therefore, combining morphological (TEM) and molecular analyses by sequencing the ITS, 28S and rbcL markers, eight species were identified from 83 isolated monoclonal strains: P. calliantha, P. fraudulenta, P. delicatissima, P. galaxiae, P. mannii, P. multistriata, P. pungens and P. subfraudulenta. A genetic comparison between the isolated strains and other strains in the Mediterranean was carried out and rbcL was inspected as a potential barcode marker in respect to our results. This is the first study in the Gulf of Trieste on Pseudo-nitzschia time series from a long-term ecological research (LTER) site coupled with molecular data. We show that meaningful ecological conclusions can be drawn by applying integrative methodology, as opposed to the approach that only considers species complexes. The results of this work will provide guidance for further monitoring efforts as well as research activities, including population genetics and genomics, associated with seasonal distribution and toxicity profiles.
Keywords: Pseudo-nitzschia, morphology, phylogeny, seasonality, time series, Adriatic Sea
Published in DiRROS: 18.03.2020; Views: 4938; Downloads: 1732
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