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Marine underwater habitats dominated by seagrass Posidonia oceanica play an essential role in fish community assembly, affecting taxonomic and functional diversity, abundance and fish behavior. The value of seagrasses as habitat depends on the spatial arrangement of the seascape elements and the availability of alternative habitats. Little is known about the effect of the seascape context of P. oceanica meadows on fish assemblages in the Mediterranean Sea. To identify P. oceanica meadows’ relative importance as a habitat for fishes, fish communities in the Croatian Adriatic Sea were investigated, using SCUBA lure-assisted visual census. The results show a significant effect of different arrangements of P. oceanica meadows’ seascape elements and surrounding habitats on fish community structure. Fragmented mosaic meadows with P. oceanica growing directly on and between rocky-algal reefs/boulders had significantly higher fish abundances compared to both types of continuous meadows (bordering rock and bordering sand). Continuous meadows bordering sand harbored the highest number of unique species. Evidence that alternative structured habitats within proximity to seagrass beds may affect the community structure of associated fish assemblages is provided, highlighting the need to consider P. oceanica meadows’ seascape context in conservation management and experimental design for fish community structure.

Marine Protected Areas and other managed marine sites are designated to improve the status of coastal fish assemblages and protect valuable habitats. The implementation of management practices relies on data collected through monitoring activities. The monitoring of fish assemblages using the standard non-destructive methods requires significant financial resources and time. A new approach to monitoring fish assemblages in the coastal waters was recently implemented in the Mediterranean – Fish Assemblage Survey Technique (FAST). It is based on Citizen Science where trained volunteer divers collect the data following a pre-established protocol. Considering the differences in species presence/absence and their sizes between the Mediterranean and the Adriatic Sea, a modification of the method was necessary. This study presents 23 main fish species and four ‘joker’ species selected for the Croatian FAST list and their respective sizes that will be considered Large (>2/3 of the total size) for implementing the method in the Croatian part of the Adriatic Sea.

The oligotrophic Adriatic Sea is characterized during a typical summer by low productivity caused by strong water column stratification, which inhibits vertical mixing and nutrient supply to the euphotic zone. These conditions can be disrupted by transient physical forcing, which enhances nutrient fluxes and creates localized hotspots of relatively high net primary production. In this study, plankton abundance and diversity were investigated in relation to the physical forcing and nutrient concentrations in an area affected by island-trapped waves (ITWs) near Lastovo Island (Adriatic Sea). The episodic ITW events resulted in enhanced uplift and vertical excursion of the thermocline, marked by anomalously higher nutrient concentrations and a corresponding increase in net primary production in the thermocline layer. Physicochemical properties explained 11.7 % ( p  = 0.002) of the variability in micro- and nanophytoplankton and 88.9 % ( p  = 0.001) in the picoplankton community. A significant response to the ITW phenomenon in the plankton community composition ( p  = 0.001) was observed for bacterioplankton. Among the identified amplicon sequence variances, primary producers were scarce and mainly represented cyanobacteria ( Synechococcus strain CC9902), stramenopiles ( Pelagomonas ), and chlorophytes ( Ostreococcus ). The remaining amplicon sequence variances were assigned to the classes Copepoda, parasitic fungi ( Meyerozyma spp.), mixotrophic dinoflagellates (family Peridiniales, mostly the genus Blastodinium ), and parasitic Ciliophora ( Scuticociliata ). Bacterial ecological functions corresponded to chemoheterotrophic, degradation, and fermentation processes, whereas samples collected after the most intense ITW episode also showed abundant bacteria linked to microplastic degradation and parasitosis. These results highlight the ecological role of localized physical phenomena in enhancing nearshore primary productivity and fine shifts in plankton taxa in oligotrophic systems., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

We identified areas with high individual densities of the pen shell, Pinna nobilis, in two areas along the Croatian Adriatic coast. The surveys carried out in 2018 and 2019 showed population densities of approximately 9 to 13 individuals/100 m 2 . However, in 2019 a mass mortality event (MME) causing 36% to 100% mortality of this bivalve species was observed in the surveyed Croatian bays. The parasite Haplosporidium pinnae was identified by histological and molecular methods in all affected sampled individuals, while Mycobacterium sp. and Gram negative bacilli were detected in some affected and live bivalves. This finding constitutes the first record of these pathogens affecting P. nobilis in the middle Adriatic, confirming the continuous spread of the disease. Previously, the Adriatic water body was considered to be a natural shelter against the MME caused by pathogens in pen shell populations because of its distinct ecological features. The Adriatic Sea is a semi-closed water body with the largest continental shelf in the Mediterranean Sea, and due to its geomorphology and bathymetry, it is a sea with distinct characteristics. Monitoring plans and further studies in the Adriatic bays are now a priority for mitigating the high risk of extinction and working toward the conservation of this protected species., (Copyright © 2020 Elsevier Inc. All rights reserved.)

This study estimates levels of marine litter including plastics (macro-, meso- and microplastics) in sediments collected in shallow marine water from Croatia (Central Adriatic Sea). Selected sampling areas are characterized by different human pressure: Silba is highly stressed by tourism while Grebena is listed as marine protected area (MPA) of future institution. Obtained results on marine litter in sediments are correlated to ecological features recorded in each sampling site. Marine litter in collected sediments ranged within 180-528 items/kg d.w. Macroplastics were not recorded while mesoplastics were 1.3-4.8%. On a general basis, fibres are higher than microplastics. In Južni Greben, level of fragments higher than fibres was recorded. A slight significance of the factor "water depth" was evidenced by the statistical analyses exploring relationships among marine litter and ecological features. Furthermore, Silba and Grebena Islands showed a significant different assessment of size, shape and colour features. These results suggest different sources/dynamics affecting marine litter recorded in marine areas stressed by tourism compared to MPA., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This paper reports baseline levels of litter (macro, meso and microplastics) in sediments collected from different areas of the Croatian MPA of the Natural Park of Telaščica bay (Adriatic Sea, GSA n. 17). The distribution of total abundance according to size, for all analysed locations evidences that microplastics are the dominant fraction concerning item's numbers. In all analysed samples no macroplastics were found, while microplastics are 88.71% and mesoplastics are 11.29% of the total., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This research aims to define for the first time levels and patterns of different litter groups (macro, meso and microplastics) in sediments from a marine area designed for the institution of a new marine protected area (Aeolian Archipelago, Italy). Microplastics resulted the principal group and found in all samples analyzed, with shape and colours variable between different sampling sites. MPs levels measured in this study are similar to values recorded in harbour sites and lower than reported in Adriatic Sea, while macroplastics levels are notably lower than in harbor sites. Sediment grain-size and island extent resulted not significant in determining levels and distribution of plastic debris among islands. In the future, following the establishment of the MPA in the study area, these basic data will be useful to check for potential protective effects on the levels and distribution of plastic debris., (Copyright © 2016 Elsevier Ltd. All rights reserved.)