Institute of Oceanography and Fisheries

Magnesium (Mg) isotopes in biogenic marine carbonates offer a promising proxy for reconstructing past seawater Mg isotope compositions, thereby providing insights into the mechanisms driving Cenozoic climate cooling. This study assesses the bivalve Glycymeris as an alternative geochemical archive to foraminifera and corals, which have yielded inconsistent results in previous work. Specimens from three modern species— Glycymeris bimaculata , G. nummaria , and G. pilosa —spanning a range of ontogenetic ages from 1 to 16 were collected from the Adriatic Sea. Shell samples were taken from the ventral margins of individuals, with one representative individual analyzed per species. Magnesium was rigorously purified using a three-step chromatographic protocol that combined a semi-automated prepFAST system with manual ion-exchange chromatography. Results show that Mg isotope fractionation increases with ontogenetic age in both ventral-margin and intra-shell samples. A geometric model based on relative shell areas was developed to quantify precipitation rates that reveals a precipitation-rate dependence, which is consistent with abiogenic calcite experiments. These findings indicate that Mg isotope fractionation in Glycymeris shells is not species-specific and that these bivalves are potential archives for reconstructing past seawater Mg isotope variations. • δ 26 Mg shows consistent trends across three Glycymeris species with ontogenetic age. • A geometric growth model was developed for the shells. • Intra-shell δ 26 Mg variations correlate with shell growth rate. • Glycymeris shells show potential as archives of past seawater δ 26 Mg.

Pseudomonas aeruginosa is one of the leading causes of ventilator-associated pneumonia (VAP) and ventilator-associated tracheobronchitis (VAT), with a worldwide spread of difficult-to-treat high-risk clones. This study aimed to investigate the virulence potential and to characterize phenotypic and genotypic antimicrobial resistance (AMR) in P. aeruginosa causing VAP/VAT in the Intensive Care Unit (ICU), University Hospital of Split, Croatia. The study included P. aeruginosa isolates obtained from ICU patients who met the criteria for VAP or VAT, between January 2023 and January 2024. Isolates were identified using MALDI-TOF MS and tested for antimicrobial susceptibility (AST). A subset of phenotypically multidrug-resistant (MDR) isolates was further analyzed using whole-genome sequencing (WGS) and multilocus sequence typing. A high rate of resistance was detected to ceftazidime (23.4%), imipenem (39.6%), and meropenem (43.8%). WGS confirmed the presence of multiple AMR genes, including the blaVIM-2 gene, whose genetic environment highlights a complex MDR locus integrating multiple AMR determinants and mobile genetic elements. All tested isolates possessed genes for class C (blaPDC34, blaPDC374 or blaPDC16) and class D (blaOXA-2, blaOXA-10 or blaOXA-50) β-lactamases, fosA, aph(3')-IIb and crpP genes. Additionally, WGS analysis revealed the presence of numerous virulence genes including those for adherence (Type IV pili and Fap protein production), motility (such as flgF), biofilm formation (e.g., algE and mucE), quorum sensing (lasI, lasR, rhlI and rhlR), exotoxin (toxA and plcH) and exoenzyme activity (exoU, exoT, exoS, exoY, pcrV, hcp1 and lasA). The isolates belonged to four different sequence types: ST235, ST446, the high-risk ST253 and the widely distributed ST395. Phylogenomic comparison demonstrated that the isolates from this study do not originate from a single clonal source, but instead represent multiple globally distributed high-risk P. aeruginosa lineages introduced into the clinical setting. Due to the emergence of high-risk clones with broad AMR and strong virulence potential, ineffectiveness of standard empirical therapy may be anticipated, highlighting the urgent need for new therapeutic approaches (including those targeting major virulence factors).

Mycotoxins are toxic secondary metabolites produced by filamentous fungi which are commonly found as natural contaminants in food and feed worldwide. In recent years, aquaculture research has increasingly focused on changing fish feed by replacing traditional protein sources with plant-based and insect ingredients to promote sustainability. However, this shift has raised concerns about mycotoxin contamination in farmed fish, fish products, and processing by-products. As a result, the pursuit of sustainable aquaculture practices may inadvertently increase the risk of mycotoxin exposure. To date, studies on freshwater fish have focused primarily on regulated mycotoxins, and the findings have demonstrated their occurrence in muscle, liver, intestine, ovaries, and hepatopancreas. Most studies have investigated aflatoxin B1, and its presence has been confirmed in the muscle tissue of several fish species. In marine fish, research has encompassed a broader spectrum of mycotoxins, including emerging and masked forms, across multiple tissues and organs. However, across various studies, conflicting results have been reported regarding the occurrence of emerging mycotoxins, particularly enniatins and beauvericin. This paper reviews current research on mycotoxin contamination in farmed fish, summarising detected levels across freshwater and marine species and in derived products, and also discusses future perspectives on mycotoxin risks in sustainable aquaculture.

This study examines the genomic composition and resistance potential of eight putative plasmid-derived contig assemblies reconstructed from marine Enterobacterales isolated in the central Adriatic Sea. Using a combination of Illumina-based whole genome sequencing, de novo assembly, and a multi-tool bioinformatics pipeline, we annotated antimicrobial resistance genes (ARGs), insertion sequences (ISs), and plasmid replicon types. Clinically significant resistance markers such as blaKPC, blaTEM, aacA4, tetA, and folP were identified, frequently co-localised with mobile genetic elements including IS110, IS4, and IS1182. The plasmid-associated contigs were assigned to MOBP and MOBQ types and contained replicon markers (IncP6, IncA/C2) characteristic of broad-host-range plasmids. Our findings provide valuable insight into the plasmidome of environmental Enterobacterales, emphasising the role of coastal pollution in shaping the distribution and potential mobility of antimicrobial resistance genes. This supports the One Health framework by linking environmental reservoirs to clinically relevant resistance mechanisms.

Oligotrophic marine systems respond rapidly to episodic nutrient enrichment with an increase in productivity at all trophic levels. In order to link the prevailing hydrodynamic processes with plankton indicators, we investigated the biomass, composition and production of plankton communities as well as the physical and chemical parameters in the central Adriatic areas of Blitvenica and Jabuka at three stations during two seasons (November 2020 and May 2021). The analysis of thermohaline properties and horizontal currents showed that warmer and more saline water from the southern Adriatic flowed along the coast in November and that there was a strong freshwater influence in May. Different hydrodynamic processes in the different seasons lead to different nutrient sources, e.g. higher concentrations of phosphate and inorganic nitrogen in November were the result of the advection of warmer and saltier water from the southern Adriatic, while May was characterized by a higher concentration of organic nitrogen and the influence of the Krka River. Both situations were also reflected in the composition and size of the phytoplankton, zooplankton and bacterioplankton community. In November, picoplankton dominated the phytoplankton biomass and primary production, while in May, nanoplankton predominated. Microplankton was most strongly represented in the lower layers during both sampling season characterized by certain phytoplankton species. The development of larger phytoplankton cells in May favored the development of zooplankton, which was reflected in an increase in the number of copepods and a lower diversity compared to November. Of all the biological parameters analysed, only bacterial production (BP) was high in May at the station in Blitvenica (BL1). • Plankton communities respond to mesoscale hydrodynamic fluctuations. • Advection of water from the southern Adriatic resulted in a deeper mixed layer. • Advection of warmer and saltier water is favoured by coccolithophores. • Oligotrophic marine systems respond rapidly to episodic nutrient enrichment from river discharges. • The deep chlorophyll maximum (DCM) is composed of different sizes and taxonomic groups of phytoplankton in different seasons. • The high bacterial production (BP) in the entire water column is the result of the supply of organic nitrogen by the freshwater, but also the excretion of organic material and nutrients by certain groups of phytoplankton and zooplankton.

High-frequency sea-level oscillations (with periods shorter than three hours) occasionally reach significant amplitudes along the eastern Adriatic coast, posing risks to coastal infrastructure and communities. These oscillations are often driven by rapid atmospheric pressure disturbances that travel towards the shore, where local topography can amplify the resulting sea-level response - especially in bays and harbors along the Croatian coast. The most extreme events of this type are meteotsunamis. Understanding the relationship between atmospheric forcing and sea-level response is crucial for developing meteotsunami forecasting and early warning systems in vulnerable Adriatic locations.In this study, we explore the connection between high-frequency components of 1-minute atmospheric pressure and sea-level measurements from a network of microbarograph and tide-gauge stations located in the central Adriatic along both its eastern and western coast. The measurements that cover the period from May 2017 to October 2024 underwent rigorous quality control, addressing issues such as outliers, duplicates, and data gaps. To explore atmospheric pressure and sea-level relationships, we applied multiple methods for identifying extreme events, including variance-based and wave-height-based approaches. We then examined correlations across station pairs using various temporal offsets (0 to 480 minutes) between atmospheric and ocean series, all in order to determine what kind of atmospheric pressure oscillations tend to precede extreme sea-level oscillations.Preliminary results suggest varying degrees of correlation between atmospheric pressure and sea-level oscillations, with stronger connections observed for certain station pairs, possibly influenced by geographic proximity. In some cases, the strongest sea-level events were preceded by distinct pressure jumps, suggesting a delayed sea-level response, while in others, their co-occurrence appeared more synchronized. Both the variance-based and wave-height-based approaches provided broadly similar patterns, though the variance-based method showed limitations in capturing very short-lived atmospheric pressure disturbances. Ongoing analyses aim to refine these findings by testing alternative methods, involving event-based extraction of extremes, and estimating the propagation velocity of atmospheric disturbances - steps intended to enhance our understanding and improve the predictive capabilities of future high-frequency sea-level oscillation monitoring and warning systems.

Abstract. The Adriatic Sea (eastern Mediterranean Basin) is traditionally considered a natural laboratory for studying a number of oceanographic processes of global interest, including coastal dynamics, dense water formation, and thermohaline circulation. More recently, the intensification of the effects of climate change and the increasing awareness of its possible consequences on the natural and socio-economic assets of the Adriatic Basin have opened new research questions and reframed most of the existing ones into a multi-decadal timescale. In this perspective, a description of the possible evolution of the physical oceanographic processes is one of the key requirements for addressing the multi-disciplinary challenges set by climate change, but up to now it has not been possible to combine, for this basin, a sufficiently high resolution in the process description with an estimate of the uncertainty associated with the predictions. This work presents an ensemble modelling approach (AdriE – Adriatic Sea Ensemble) for the kilometre-scale description of hydrodynamics in the Adriatic Sea in an end-of-century time frame. Addressing 3D circulation and thermohaline dynamics within the Regional Ocean Modelling System (ROMS), the ensemble consists of six climate runs encompassing the period from 1987 to 2100 in a severe RCP8.5 scenario forced by the SMHI-RCA4 regional climate model, driven by as many different CMIP5 general climate models made available within the EURO-CORDEX initiative. The climate ensemble is flanked by a dedicated evaluation run for the 1987–2010 period, in which SMHI-RCA4 has been driven by reanalysis fields approximating the best available boundary conditions, thus isolating the intrinsic sources of uncertainty in the RCA4–ROMS modelling chain. In order to allow a direct comparison, the assessment of the model skills in the evaluation run borrows, as far as possible, data and approaches used for the evaluation of a recent kilometre-scale, multi-decadal modelling effort for this region. The model performances are mostly aligned with the state-of-the-art reference. In particular, good results in describing the main features of marine heatwaves and cold spells, such as timing, intensity, and interannual variability, indicate that the AdriE ensemble can effectively be used for studies on the occurrence and effects of thermal extremes in the basin. Future projections suggest an increase in temperature and salinity at upper and intermediate depths, resulting in an overall decrease in water density and possibly in deep ventilation rates. Projected variations are stronger in summer and autumn, and in these seasons the ensemble range is larger than the spatial variability of the quantities and occasionally comparable with the intensity of the climate signal, highlighting the importance of an ensemble approach to treat the climate variability at this timescale. The dataset presented in this study, which can be used for the analysis of coastal and continental margin processes of general interest, is fully available upon request to the corresponding author, and monthly averages of the main quantities are available for each run on a dedicated Zenodo repository.

The study presents an exceptional number of records of the devil firefish Pterois miles along the Croatian coast. These records are based on 122 confirmed sightings of the species recorded between June 2024 and January 2025, providing evidence of a rapid and extensive expansion of the species in the eastern Adriatic waters. Most records originated from citizen science via direct reports of sightings, complemented by monitoring of social networks and online media platforms. The highest number of sightings was recorded around the islands of Lastovo and Vis, while the area around Dubrovnik had the highest number of sightings along the mainland coast. The majority of individuals (72.7%) were sighted within the first 15 meters of depth, with most individuals estimated to be 15 cm or smaller in length. No correlations between depths and lengths of individuals, as well as between time and latitude of sighting were detected. Most sightings occurred during diving activities, with a few involving captured specimens. The observed expansion is likely a result of larval transport via sea currents and subsequent settlement, as the pattern of records aligns with general circulation patterns along the eastern Adriatic coast. Given the species’ biological traits, which facilitate rapid and extensive establishment in invaded areas, this expansion poses certain ecological risks, particularly in key coastal habitats that host ecologically and economically important fish species. We encourage targeted removal strategies, particularly in ecologically significant areas such as Marine Protected Areas (MPAs), commercialization of the species and reduction of fishing pressure on natural predators as mitigation measures.