The noble pen shell ( Pinna nobilis ) is experiencing mass mortality events across the Mediterranean Sea. In the northern Adriatic, as in many other regions, soft-bottom habitats are now covered with numerous empty shells. To assess their ecological role, we conducted underwater SCUBA surveys using quadrats in 2023 and 2024. We examined the function of empty shells as refuges for motile epibenthic macroinvertebrates across vegetated and unvegetated habitats. Specifically, we compared invertebrate diversity among habitats with and without shells, assessed the influence of shell orientation on community composition, and identified taxa characteristic of each habitat type using non-invasive methods that did not displace shells. Most shells remained upright, though their density and orientation varied among the six study locations. We recorded fauna from seven classes, with malacostracans and gastropods being the most species-rich groups. Biodiversity metrics differed markedly among the four microhabitat types (sediment, sediment with shells, meadow, meadow with shells), reaching the highest values in meadows with shells and the lowest in bare sediment. Malacostracans and polyplacophorans were significantly more abundant in samples containing shells, while other taxa showed no consistent trends. Shell orientation did not affect the composition of motile fauna, but distinct assemblages were associated with specific habitat types. These findings highlight the ecological importance of P. nobilis shells as microhabitats that enhance coastal biodiversity even after the death of the organism and underline the potential negative consequences of their degradation or removal. • Empty Pinna nobilis shells provide refuge for motile macroinvertebrates. • Biodiversity peaks in seagrass meadows with empty P. nobilis shells. • Shell orientation does not influence community composition or diversity indices. • Assemblages differ among microhabitats, showing unique species–habitat associations. • Empty shells enhance habitat complexity after mass mortality.

Abstract In this study, we investigate a series of significant flooding events that occurred in the northern Adriatic Sea during December 2019. Despite their intensity, none of the existing operational forecasting systems was able to predict these events accurately. To understand the underlying causes, we analysed wind and sea‐level observations from several key locations along the Adriatic coast. Additionally, we employed reanalysis wind and air pressure datasets and a high‐resolution finite‐element hydrodynamic model to explore the hypothesis of a wind‐induced sea‐level resonance further. Our results consistently support the idea that quasi‐periodic wind oscillations, associated with the passage of multiple cyclones, excited the basin's fundamental barotropic mode. Finally, we developed a simplified analytical model that, despite some approximations, successfully reproduces the main features of the observed sea‐level oscillations. These findings highlight the importance of resonance mechanisms in coastal flooding and suggest potential improvements for future forecasting systems.

Divergent and habitat-specific responses of benthic communities to environmental and climate change in a twenty-year time series (2004-2023) in the Northern Adriatic.

Migratory birds crossing large ecological barriers can exhibit significant plasticity in their circadian movement patterns, e.g., shifting from nocturnal to continuous flight over seas. But substantial plasticity in the circadian patterns of active migration has also been reported in other birds, such as most intra-Palearctic dabbling ducks, that do not face major ecological barriers en route. Yet, the factors driving such behavioural variation in these species remain poorly understood. We investigated how biotic and abiotic factors influenced circadian movement patterns and seasonal migratory schedules during pre-breeding migration of GPS-tracked Northern pintails (Anas acuta) tagged in late winter in northern Adriatic wetlands (Italy) and migrating across Eurasia towards their breeding areas. We classified behaviours from GPS data and estimated the probability of being in active migration as a function of biome, altitude of the sun above the horizon, average ground temperature, and orthodromic distance from the breeding site. While showing a consistent preference for conditions of low (and decreasing) sun altitude throughout migration (n = 22 pintails, n = 25 complete migration events), we observed a gradual shift towards diurnal flight along the movement path, with the level of diurnality varying according to the specific biome encountered and, likely, to the potential exposure to predators in forested areas, across latitudes. Stopovers were longer in the first half of migration and shorter and more frequent as pintails neared the breeding grounds (located mainly in the Russian Arctic). Although active migration segments were covered at very high speeds, the overall migration pace was consistently slow, suggesting a tendency to follow seasonal cues en route. Our study provided evidence that circadian migration patterns and seasonal migratory schedules in pintails were continuously adjusted in response to the environmental conditions encountered during migration. This variation was not solely due to the steep reduction in dark hours as individuals migrated northeast, nor to the increasing urgency to reach the breeding grounds. Rather, it likely resulted from an adaptation to ecological contexts favouring daytime migration, counteracted by the necessity of waiting for environmental conditions to become suitable for breeding.

This paper investigates the Mesolithic-Neolithic transition in the northern Adriatic by testing theoretical models of Neolithization through a review of the available radiocarbon evidence. While our understanding of the spread of farming in Europe has improved significantly in recent years, especially due to an increasing body of ancient DNA evidence, this does not seem to be the case for the northern Adriatic. Here, not only is there a lack of ancient genetic material, but significant changes in landscape configuration caused by postglacial sea-level rise have affected archaeological visibility. Unresolved aspects of the transition include the scarcity of Late Mesolithic sites, the debated role of hunter-gatherers, and the swift establishment of a fully developed farming economy. In this paper, chronological data obtained from radiocarbon dating is used to argue for a ‘spectrum of possibilities’, with different dynamics in different subregions and different lines of evidence supporting distinct mechanisms of Neolithization, often with an equifinal outcome. It is shown that the Mesolithic-Neolithic transition in the northern Adriatic occurred over the entirety of the sixth millennium BC, but also that different readings of the data suggest leapfrog colonization and frontier mobility occurring in different areas, or even in a single subregion. Online Supplementary MaterialSupplement 1

Haplosporidium edule is a haplosporidian parasite originally described in the common edible cockle (Cerastoderma edule) along the European Atlantic coast. In this study, we report the first detection of H. edule in the olive-green cockle (Cerastoderma glaucum) from the northern Adriatic Sea, representing both a novel host record and a new geographic occurrence. During a cross-sectional study conducted in May 2019, 90 C. glaucum specimens were collected from three lagoon sites in northeastern Italy. Histological examination of soft tissues revealed haplosporidian developmental stages, including plasmodia, sporoblasts and mature spores, within connective tissues of the mantle, digestive gland, gills and between gonadal tubules in eight individuals from the Goro Lagoon. Molecular characterization based on a fragment of the small subunit ribosomal DNA showed high similarity with the previously published H. edule sequence. Host identification was confirmed through cytochrome c oxidase subunit I barcoding together with morphological and histological analyses. These findings indicate that H. edule has a broader host range than previously recognized. Although prevalence was relatively low, the detection of this parasite in a new host species and geographic area highlights the importance of continued surveillance, particularly in the context of climate change, shellfish translocations and the expansion of aquaculture activities.

Abstract This study critically analyses the main narratives surrounding the Atlantic blue crab ( Callinectes sapidus ) in the Lagoon of Venice. We used a mixed‐method approach, performing a qualitative discourse analysis on a sample of 68 textual sources to identify the narratives across two sectors in the management of the case study: media and politics, and scientific research. The texts were organized into a database of short sequences of words. Each sequence was assigned to a specific category and subcategory. The database was then quantitatively analysed using distribution and word count analyses. Four master narratives were identified and then discussed in the context of existing critical literature: ‘We have transformed the threat of blue crabs into an opportunity’; ‘We are at war against the blue crab’; ‘Consumption is a solution’; ‘The blue crab is a product’. The study revealed three pivotal findings: in the media and politics discourse, the militarization of language is still prevalent; the scientific debate stresses the importance of efficient exploitation and marketing as the main solution to manage the blue crab; both scientific and public debate use specific words and rhetorical tactics to transform blue crabs into commodities. We finally provide four recommendations for relevant professionals in the field of invasive alien species management. Read the free Plain Language Summary for this article on the Journal blog.

The consequences of historical and long-term human impacts on non-commercial marine benthic species are poorly known due to temporally limited monitoring data. Skeletal remains preserved in sediment cores provide a historical archive for reconstructing ecological baselines prior to anthropogenic impacts and can document population fluctuations not captured by recent ecological surveys. Here, we traced a unique Holocene record of the echinoid Echinocyamus pusillus from sediment cores and grab samples in the northern Adriatic Sea, a region affected by human disturbances over millennia. The exceptional preservation of the small luminacean archives long-term persistence of this species over the past ~11000 yr, providing a baseline for understanding long-term dynamics of echinoid populations. The radiocarbon age-dating of multiple specimens from the surface sediment layer revealed high abundance of E. pusillus tests from the 18 th and early 19 th century but an absence of individuals that died within the last ~100 yr. This pattern suggests a dramatic decline in test production and thus population densities since the late 19 th century, likely linked to intensified siltation, trawling-induced sediment disturbance, eutrophication, and hypoxia in the northern Adriatic Sea. Our results highlight the vulnerability of non-commercial or poorly studied benthic species to human-driven habitat degradation, which is often difficult to assess without palaeoecological data due to the historical legacy of many human impacts.

Phytoplankton is a key component of marine ecosystems and a sensitive indicator of environmental change. In this study, light microscopy (LM) and DNA metabarcoding (18S-V4, 18S-V9, and rbcL) were combined to assess differences in phytoplankton diversity and community structure across three LTER sites in the northern Adriatic Sea, and to evaluate the methodological effects on community assessment. A total of 329 genera and 527 species were recorded by integrating both the approaches. Metabarcoding (MB) revealed increased taxonomic richness than LM, particularly for dinoflagellates and small phytoflagellates, while LM was better for identifying the diatoms and coccolithophores. The rbcL marker improved the taxonomic resolution for the diatoms compared to the 18S regions. The proportion of species shared among the sites increased from 13% with LM to 33-42% with MB, suggesting that MB may effectively reduce the discrepancies observed when relying solely on LM. Cluster analysis performed on species-relative abundances grouped the samples by approaches rather than sites, showing that methodological variability exceeded the ecological differences. The relative abundance patterns differed between methods but became more comparable after applying correction factors based on the 18S rRNA gene copy numbers, particularly for the dinoflagellates. Overall, MB enhances biodiversity assessment and comparability among sites, while LM remains essential for morphological validation and for abundance assessment.

The Adriatic Sea mucilage: The history of a hidden harmful dinoflagellate bloom.

Jellyfish are increasingly recognized as a significant contributor to marine organic matter (OM) on a global scale, with implications for ecosystem dynamics. While the role of jellyfish detritus in microbial nutrient cycling has been explored, the contribution of OM released by live jellyfish—primarily as mucus (hereinafter referred to as mucus-associated OM, or MAOM)—remains understudied. This study investigates the release of organic and inorganic nutrients through MAOM from live jellyfish and their effects on ambient microbial communities in the northern Adriatic Sea using a series of leaching and short-term microcosm experiments. Our results show that per gram of MAOM dry weight from the jellyfish Aurelia spp, approximatively 2 µmol of phosphate, 4 µmol of dissolved inorganic nitrogen, 18 µmol dissolved organic nitrogen, 134 µmol of dissolved organic carbon and 15 µmol of dissolved free amino acids can be released in the ambient seawater in 24 h. Almost half of the OM is released as dissolved OM (DOM), of which a substantial part is low molecular weight (<1 kDa) molecules. During the first 20 h, the DOM fraction of MAOM was rapidly consumed by the ambient microbial community without a corresponding increase in biomass, likely due to nitrogen limitation. In the subsequent 22 h, microbial growth accelerated to 0.19 ± 0.03 h−1 until phosphate became limiting, leading to a sharp decline in microbial production. Our metagenomics analysis revealed that the MAOM-degrading microbial community, dominated by Gammaproteobacteria opportunistic copiotrophs, exhibited increased functional capacity for nutrient assimilation and OM degradation, particularly in the transport and metabolism of amino acids (particularly glycine and taurine) and phosphorus. These traits mirror those found in detritus-degrading microbial communities, suggesting that jellyfish blooms promote the emergence of specialized microbial consortia with shared metabolic capabilities. Taken together, our findings highlight that live jellyfish, through the release of OM, play an active and previously underappreciated role in shaping ambient microbial community dynamics and nutrient fluxes in marine systems affected by jellyfish blooms.

Understanding the impact of climate change on tourism is vital for the economies that rely on it. The tourism sector in Croatia, a country with diverse climatic regions, but also diverse features of tourism, is particularly sensitive to changes in climate variables such as 2 m air temperature and precipitation totals. This study analyzes trends in these two key climate variables from 1961 to 2024 across five representative climatic regions: the-mountainous Lika region (Ličko-senjska County), the Kvarner region on the northern Adriatic coast (Primorsko-goranska County), the Zadar region on the central Adriatic coast (Zadarska Counties), and northern continental Croatia (Varaždinska and Međimurje Counties). Linear trends, 5-year moving averages, and comparisons between two standard climate periods (1961–1990 and 1991–2020) were conducted. Using these data, the monthly self-calibrated Palmer Drought Severity Index (sc-PDSI) and Standardized Precipitation Index (SPI) for seven-time scales were calculated for the period 1961–2024 to assess drought conditions and their implications for tourism across the selected destinations. Frequencies of dry, near normal and wet months, estimated by SPI for a nine-month time scale (SPI-9) and a monthly sc-PDSI, were compared for two subperiods, 1961–1992 and 1993–2024. Meteorological data were contextualized for tourism stakeholders, with a focus on adaptation measures. Semi-structured interviews were conducted with tourism professionals in the study regions, providing qualitative insights into observed changes in climate and tourist behavior, operational challenges, adaptation strategies, level of community engagement, and opportunities envisioned. Objective climatological data were compared with the subjective perceptions of tourism experts using the principle of mixed methods, which allows for triangulation. The climatological data indicated a continuous trend of increasing mean annual air temperatures, as well as anomalies of average precipitation amount. The interviews revealed signals of emerging climate shifts, such as changes in the seasonality of visitors, concerns about water scarcity and heat stress. These findings were interpreted in the context of potential threats and opportunities for the tourism sector, highlighting region-specific adaptation strategies. By combining objective climate data with insights from tourism professionals, this study provides a comprehensive assessment of climate change impacts on tourism and informs for resilient tourism development across Croatia’s diverse regions. This paper presents a methodological framework for developing adaptation recommendations that draw on both empirical climate data and the lived experiences of tourism work practitioners.

This study investigates the intensification of drought in the continental part of the Istrian peninsula using two standardized drought indices: the Standardized Precipitation Evapotranspiration Index (SPEI) and the New Drought Index (NDI). Monthly precipitation and temperature data from the main meteorological station in Pazin, covering the period 1961–2024, were analyzed. Statistical methods, including linear regression, Mann–Kendall test, and Rescaled Adjusted Partial Sums (RAPS) analysis, were applied to detect trends and fluctuations in the time series. Results indicate a significant increase in mean annual air temperatures since the late 1990s, with particularly strong warming in summer months. Precipitation trends, although highly variable, did not show a statistically significant long-term decline. Both drought indices reveal an intensification of drought conditions after 1985, with NDI showing stronger sensitivity to temperature rise than SPEI. Seasonal analyses demonstrate that drought occurrence is most pronounced during the warm part of the year, while cumulative series indicate a shift from predominantly wet to predominantly dry conditions after the mid-1980s. The comparison of the two indices shows a high degree of agreement but also highlights the added value of NDI in detecting temperature-driven drought processes. The findings emphasize the growing risk of more frequent and severe droughts in humid regions of Istria, including the potential for flash drought events. These results may support the development of improved drought early-warning systems and adaptation strategies in the Mediterranean context.

This study reports three cases of pigmentation disorders in Squalus acanthias from the Gulf of Venice. Two specimens exhibited spotless phenotypes, whereas one exhibited hypermelanism. Morphological assessments were conducted for two individuals, alongside genetic analysis of mitochondrial genes to determine phylogeographic relationships. Both specimens belonged to the South Pacific/Atlantic/Mediterranean haplogroup, with the first one associated with the main haplotype and the second one linked to a rarer haplotype. This study emphasizes the need for proper identification based on morphology and genetics when pigment disorders hinder a clear-cut species assignment.

Aim: To analyze the spatiotemporal distribution and accumulation patterns of floating marine litter in the Adriatic Sea from 2015 to 2021 using satellite observations, with particular focus on identifying regional variability and dominant transport mechanisms. Methods: In this observational study, we used satellite data from the Copernicus Sentinel-2/MultiSpectral Instrument L1C system to estimate marine litter presence across the Adriatic Sea from July 2015 to September 2021. The dataset includes records of pixels per litter windrow (PLW), representing spectral reflectance indicators of floating plastic-like debris. We performed analyses on annual and monthly scales, focusing on four zones: Italy (zones A and B), Croatia (zone C), and Albania (zone D). We assessed variability using boxplot metrics and interpreted spatiotemporal patterns in the context of oceanographic features, wind patterns, and riverine inputs. Results: Zone A had consistently higher PLW values across the study period, making it the most polluted area. Litter was probably transported along the western Adriatic coast by the Western Adriatic Current (WAC) toward the south, with partial redistribution toward the eastern coast. Zones B and D showed pronounced annual and seasonal variability, with peaks in 2017, 2019, and 2021, while zone C showed less consistent patterns. Monthly trends revealed increased litter presence in warmer months, coinciding with higher tourist activity and riverine discharges. There was a marked increase in the PLW difference between zones A and B in two periods, 2015–2017 and 2018–2021, potentially due to litter sinking, WAC meandering, or cleanup efforts. Conclusions: Satellite remote sensing can help us identify marine litter hotspots and understand their seasonal and spatial dynamics. Our findings highlight persistent pollution in the northern Adriatic and the role of currents and riverine inputs in shaping litter distribution. Long-term monitoring and integrated waste management strategies are essential for effective mitigation.

This paper examines interlace sculpture primarily from Lobor, while also considering pieces from Sisak and Slivnica, placing them in the context of the Christianization of the region south of the Drava River following the Frankish conquests. It highlights the role of Aquileia as a missionary center in this process. The study is based on the material remains of early medieval liturgical stone furnishings discovered at these sites. Analysis of the sculptures reveals stylistic and iconographic parallels with pre-Romanesque monuments from the northern Adriatic and the former Lombard Kingdom, indicating the presence of stonemasons connected to Aquileian missionary circles. Lobor is particularly notable, as archaeological research demonstrates a multi-phase continuity of sacred construction from early Christianity through the Middle Ages. The paper also compares the historical context with Carantania, where interlace sculpture is associated with local Slavic princes Christianized under Salzburg missionary activity. Based on these analogies, it is proposed that the churches in Sisak and Lobor were part of a comparable political-religious strategy by local Slavic elites under the influence of Aquileia during the first half of the 9th century.

Microplastic (MP) contamination along coastlines is a globally recognized environmental concern. This paper investigates the seasonal and cross-shore distribution of large and small microplastics (LMPs and SMPs) at four sites along the Ferrara coast in the northern Adriatic Sea (Italy). A combination of sampling and analytical approaches was employed to characterize the typology, morphology, and size of MPs. A subsample of LMPs was analyzed by Raman spectroscopy to determine polymers’ composition. The mean abundances recorded were 5.66 ± 13.15 LMPs/m2 and 2402.19 ± 1169.85 SMPs/m2. Among the LMPs, pellets and fragments, essentially cream and white in color, were dominant. The samples were predominantly composed of polyethylene, polypropylene, and polyethylene terephthalate. SMPs primarily consisted of black fibers. LMPs and SMPs displayed their lowest abundances in winter and cross-shore patterns indicated preferential accumulation at dune foot and crest. Since the study sites are located downstream of the Po and Reno river mouths, urban and riverine discharges, as well as emissions from plastic-processing industries, are likely major contributors to the observed MPs.

Conservation management, aimed at mitigating the ongoing biodiversity loss, critically relies on ecosystem monitoring to enable accurate estimates of species distributions and population sizes. Environmental DNA (eDNA) analysis has become increasingly popular for non-invasive and high-throughput species assessment, including fish species diversity. Beyond the established sample collection protocols, natural samplers of eDNA (nsDNA) – organisms that trap environmental genetic material in their tissues – show considerable promise, with recent work especially demonstrating the remarkable effectiveness of sea sponges. Here, the potential of jellyfish (phylum Cnidaria) to serve as motile, marine, pelagic natural samplers of eDNA was investigated through DNA metabarcoding using fish specific primers. Jellyfish are opportunistic marine predators known to consume fish eggs and larvae and their presence has been associated with certain fish species, making them potentially useful for open water fish assessment. Four species, the many-ribbed jellyfish (Aequorea forskalea, Class Hydrozoa), the moon jelly (Aurelia solida, Class Scyphozoa, Order Semaeostomeae), the barrel jellyfish (Rhizostoma pulmo Class Scyphozoa, Order Rhizostomeae) and the fried-egg jellyfish Cotylorhiza tuberculata (Class Scyphozoa, Order Rhizostomeae) were collected from the Italian waters of the Gulf of Trieste (northern Adriatic Sea) and nsDNA isolated, sequenced and analysed. Across all species, 28 fish Molecular Operational Taxonomic Units (MOTUs) were detected including pelagic species, benthic species likely spawning at the time of sampling, and species known to associate with the presence of jellyfish. We highlight the potential of jellyfish as tools for enhancing biodiversity monitoring, particularly in remote and inaccessible areas where conventional surveys may be difficult to employ.

Brown algal forests (Cystoseira sensu lato) are key habitat-forming components of temperate rocky coasts but have experienced widespread decline across the Mediterranean Sea. This study investigates the current distribution and potential future shifts in brown algal forests across the Adriatic Sea under ongoing climate change. We combined non-destructive field-based mapping along the Slovenian coastline with remote-sensing products and spatial environmental predictors to model basin-wide habitat suitability. A multiscale geographically weighted regression (MGWR) framework was applied to account for spatial non-stationarity and to explicitly capture the fact that environmental drivers of habitat suitability operate at different spatial scales—an assumption that global models such as GAM or standard GWR cannot adequately address. Habitat suitability maps were generated for present-day conditions and projected under mid- and late-century climate scenarios. The results reveal pronounced latitudinal gradients, identify areas of ongoing canopy decline in the northern Adriatic, and highlight parts of the southern Adriatic as potential climate refugia. Overall, the study demonstrates a likely north–south contraction of suitable habitat for brown algal forests and underscores the value of multiscale spatial modelling for informing marine spatial planning, conservation prioritization, and climate-adaptive restoration under European policy frameworks.

The significant increase in the number of calls by larger container ships also has an impact on productivity and therefore on the performance of container ports in the northern Adriatic. The productivity of a container terminal depends heavily on the processes at the berth, yard and in the gate area. In our analysis, we have therefore analysed the current capacity and operational performance of each terminal subsystem using KPIs (Key Performance Indicator) and outlined the investment plans required to enable the ports of Koper, Trieste and Rijeka to accommodate larger container vessels. These container ports handle less than 2.4 million TEU per year (2024), which is below what they could achieve given the backhaul market. Analyses have shown that improving the productivity of loading and unloading in the berth area is an effective measure to increase container traffic in the ports of the North Adriatic and improve their market share. Investments in the procurement of new quay cranes, increasing the draught at the berths and expanding the berths play a key role in this. Only with timely measures will the ports of the northern Adriatic be able to compete with their northern European rivals.