The great white shark, Carcharodon carcharias (Linnaeus, 1758), is a well-known predatory species that inhabits a wide geographic range, including the Adriatic Sea. A marked decline in the abundance of its Mediterranean population has been documented over recent decades, making research on this species in its natural environment increasingly difficult. This study documents two contemporary records of young-of-the-year individuals recorded in 2018 and 2025 off the coasts of Croatia and Montenegro, respectively. Both records were sourced from local fisheries and were subsequently reported to scientists through citizen science. The individual reported from Montenegro was photographed and released unharmed while still in the water. This study further highlights the importance of citizen science in documenting occurrences of elusive elasmobranchs such as the great white shark and in educating fishers through a bottom-up approach. Together with the recently recorded young-of-the-year specimen in this area, these observations suggest that the Eastern Adriatic Sea may represent a contemporary nursery area for the great white shark, although this hypothesis remains to be verified.

The Mediterranean monk seal (Monachus monachus) is sporadically reappearing in the eastern Adriatic, but the capacity of this region to support transient individuals or future recolonisation remains poorly understood from a prey-resource perspective. We assessed the status and multi-year trends of key prey taxa known to constitute important components of monk seal diets by integrating three complementary indicators: fishery-independent biomass indices from the MEDITS trawl survey (2002-2025), fishery-dependent landings per unit effort from small-scale coastal fisheries (SSF LPUE) monitored under the EU DCF (2012-2025), and official national landing statistics (2012-2024). Species-specific trend signals were standardised and combined using a reliability-weighted traffic-light framework to classify relative prey availability as improving (Green), stable and/or inconsistent (Yellow) or declining (Red). Among 12 evaluated prey species, 6 were classified as stable or inconsistent, 4 as improving and 2 as declining. Improving classifications were driven mainly by positive MEDITS trends for Pagellus erythrinus, Pagellus bogaraveo and Mullus barbatus, and by concordant positive signals for Scorpaena scrofa. Declining classifications indicated consistent negative trends for Conger conger, and mixed but overall negative evidence for Sepia officinalis, driven primarily by fishery-independent and landings trends. Overall, the eastern Adriatic prey base appears heterogeneous rather than uniformly depleted, with improving signals restricted to a few demersal fishes and declining signals concentrated in selected high-value prey. These findings suggest that prey availability is unlikely to represent a basin-wide barrier to monk seal recolonisation, but may impose local constraints where declining prey resources overlap with intense coastal fisheries. The proposed framework identifies priority taxa and nearshore data gaps for targeted monitoring and provides a basis for more spatially explicit assessments of monk seal habitat suitability in the Adriatic.

The spread of aquatic non-indigenous species (NIS) is recognised as a major threat to the recipient regions ecosystems. The present study reviewed all NIS that have been introduced to the marine waters of the European Union (EU) until 2021, and their introduction pathways. Further, the study statistically analysed temporal trends in new NIS introductions and addressed uncertainties in relation to transporting pathways. Time-series analyses indicated that the observed trends in new NIS introductions have followed smoothly increasing trajectories for the entire study area, Mediterranean Sea, North-East Atlantic Ocean, and the Baltic Sea, whereas abrupt increase was detected for the Black Sea. It is noteworthy that the increasing trends started to slow down at the end of 2010s. Strongly increased research interest towards marine invasions since the early 2000s, and new environmental policies likely affected the observed trends. Future updates will be key to assessing whether this slowdown is truly a persisting trend or only an anomaly in the long term. The pathway assessment suffered from notable uncertainties, as the assigned confidence levels for pathways were low or unassigned for a large proportion of the introduced NIS in all study regions. Transport by shipping vectors was assigned as the most common pathway (51%) for new NIS introductions to EU seas, although there was very rarely direct evidence of this. The study highlights the need to overcome the pathway uncertainties, as robust information on introduction pathways is critical to manage new NIS introductions effectively.

Marine litter is an issue of growing concern in the Mediterranean, one of the most polluted regions in the world. In the marine environment, floating marine litter (FML) can pose a threat, but also represent a short-term habitat for various marine organisms, including fish that can temporarily reside in these unique surroundings. However, unlike the FADs, the role of FML as habitat, shelter or dispersal vector for fish remains poorly documented, and insufficiently is known about the ecological functions of these artificial habitats or associated behavioural responses of fish. This study presents the diversity and abundance of fishes associated with FML. Data were collected accidently during other research and through contributions from non-scientific observers in fisheries and maritime traffic over the last two decades in the Croatian part of the eastern Adriatic Sea. A total of twelve fish species from eight families were identified, Balistidae being the most frequent (46.34%), followed by Carangidae (34.14%) and Serranidae (31.70%); Balistes capriscus was the most frequent species (43.34%), followed by Polyprion americanus (31.70%). Juveniles predominated with the >95% suggesting that FML may act as important shelter and nursery areas, contributing to the recruitment and redistribution of juvenile fish. Due to the limited availability of natural floating substrates in pelagic zones, fish appear to opportunistically exploit available habitats for shelter and foraging, showing similarity with FADs. This study highlights the value of Local Ecological Knowledge provided by civil society, which proved to be an important source of information on fish associated with FML.

A specimen of the smalleye squaretail, Tetragonurus cuvieri Risso, 1810, was caught on 16 February 2024 (TL = 37.2 cm, W = 277.56 g) by trawl net at approximately 100 m depth in the Mljet Channel, between the islands of Lopud and Šipan (Croatian coast). This represents the first well-documented record of T. cuvieri in the whole Adriatic Sea. Although the species has been mentioned in the checklist of Albanian fishes pertaining to Adriatic waters previously, no supporting data were provided to confirm its occurrence. The specimen was identified based on morphological characters supported by molecular analysis. Morphological and biological data are presented herein. As information on the biology, ecology, and distribution of this species in the Mediterranean Sea remains scarce, this finding extends its known range and contributes to the growing number of rare or poorly known species recently recorded in the Adriatic Sea.

Soldo [1] raises concerns about the reliability of citizen science-derived photographic records for identifying lamnid sharks in the Mediterranean Sea. Using a recently published juvenile white shark from Croatian waters [2] as a representative case, the author reinterprets the specimen as a porbeagle shark (Lamna nasus) rather than a white shark (Carcharodon carcharias), based primarily on selected dental characters. Given the critically endangered status of white sharks in the Mediterranean [3] and the limited number of confirmed observations [4,5], occurrences of the species in this region serve as valuable population data points [6,7] and merit careful examination. Species identifications and reinterpretations should therefore be well-supported, which includes verification of source materials and firsthand communication with citizen scientists, and make use of multiple diagnostic characters whenever possible. Here, we re-examined the specimen using all observable external and dental characters and show that it is consistent with the white shark. We further demonstrate that reliance on single, variably expressed traits-particularly dental characters affected by ontogeny and individual variation-can lead to erroneous identifications, and emphasize that rigorous taxonomic identifications should depend on a holistic, integrative assessment of all available morphological (and if available genetic) evidence.

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.

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.

One specimen of spearfish remora Remora brachyptera (Lowe, 1839) was caught in a bottom trawl in the eastern Adriatic Sea (Croatia) in June 2021. Morphological analysis and genetic barcoding were used for species identification. Despite references to the species inhabiting the Mediterranean Sea, no documented records have been available to substantiate its presence in the basin. This finding represents the first documented record of this species from the Adriatic and Mediterranean Seas.

The age and growth of the blackspot seabream, Pagellus bogaraveo, were determined by examining sagittal otoliths from fish sampled in the eastern Adriatic Sea. A total of 674 specimens (181 males, 90 hermaphrodites, 108 females, and 295 immatures) ranging from 8.80 to 47.27 cm (21.93 ± 9.00 cm) in total length were analyzed. The maximum observed age for the whole sample was 13 years. The sample was dominated by 1-year-old specimens as a consequence of an abundance of juvenile specimens collected by beach seines. Growth was described by the von Bertalanffy growth curve (L∞ = 52.3 cm, K = 0.15 year−1, t0 = 0.49 year, R2 = 0.97), and the growth performance index (Φ’) was 2.61. The length, width, thickness, and mass of the otoliths were compared with the total length and age of P. bogaraveo from the eastern Adriatic. The analysis showed that the measures were adequate predictors of age. These results can be of value for more effective management measures aimed at the conservation of this species.

Globally, marine bioinvasions threaten marine ecosystem structure and function, with the Mediterranean Sea being one of the most affected regions. Such invasions are expected to increase due to climate change. We conducted a risk screening of marine organisms (37 fishes, 38 invertebrates, and 9 plants), both extant and ‘horizon’ (i.e., not present in the area but likely to enter it). Based on expert knowledge for the Eastern Adriatic Sea coasts of Slovenia, Croatia, and Montenegro, screenings were conducted under both current and predicted climate conditions indicating with an increase in sea surface temperature and salinity of the Adriatic Sea together with changes in precipitation regime. Our aims were to: (1) identify non-native extant and horizon marine species that may pose threats to native biodiversity and (2) evaluate the risk of invasiveness of the selected species under current and predicted climate conditions. Of the 84 species screened, there was an increase in those ranked as ‘high risk’ from 33 (39.3%) under current climate conditions and to 47 (56.0%) under global warming scenarios. For those ranked as ‘very high’ risk, the increase was from 6 (7.1%) to 21 (25.0%). Amongst the screened species, the already established high-risk species Pacific oyster Magallana gigas and Atlantic blue crab Callinectes sapidus represent a threat to ecosystem services. Given the under-representation of marine species in the current European Union List, the species we have ranked as high to very high risk should be included.

Tremoctopods are epipelagic argonautoid octopods characterized by their expanded dorsal webs and strong sexual size dimorphism, with dwarfed males. The scarcity of taxonomic features attributed to this genus presents a challenge, and there is growing evidence of species misidentification in Tremoctopus genus on a molecular level. In this study, we investigated four female specimens of blanket octopus Tremoctopus violaceus caught by purse seine fishing in the Central Eastern Adriatic Sea in 2019. Individuals had smooth, firm and muscular bodies, dark bluish purple on the dorsal and iridescent silvery on the ventral side, with dorsal mantle lengths of 113, 82, 80 and 78 mm. The constructed phylogenetic trees based on the 16S ribosomal RNA and cytochrome c oxidase subunit I sequences of investigated Adriatic specimens and publicly available sequences showed strong support for the T. violaceus clade, consisting of individuals collected from the Adriatic Sea, Mediterranean Sea and Atlantic Ocean, with the exclusion of Indo-Pacific clade most probably corresponding to T. gracilis. To fully understand the life-history traits of Tremoctopus species, future research should focus on DNA-based methods for correct species identification combined with morphological characters, geographic distribution and ecological information.

Groupers are important predator marine fish species, and also economically important to commercial and recreational fisheries, but threatened by overfishing worldwide. The dusky grouper (Epinephelus marginatus) is the most common species that historically occurred in the southern and central Eastern Adriatic, while other species were mostly restricted to the southern part of the region or were not recorded in the Adriatic Sea. However, the warming of the sea caused by recent climate change has caused some grouper species in the Eastern Adriatic to expand northward. This spread has been poorly documented, largely because rocky coastal habitats, which are less accessible to conventional research methods that often rely on specific fishing gears, have received far less attention than other more accessible habitats i.e. soft bottoms. Reports of recent grouper expansion are primarily anecdotal and mainly based on the extensive observations of recreational fishermen who mainly utilize rocky coastal habitats. In order to gain insight into this phenomenon, we conducted a survey to investigate the distribution of groupers along the Croatian coast of the eastern Adriatic using the Local Ecological Knowledge methodology. Semi-structured interviews were carried out to record fishers' knowledge and perceptions of changes in their catches, as well as personal observations. The data collected provided information on the spatial and temporal expansion of groupers in the eastern Adriatic over the last 60 years, as perceived by local recreational fishermen.

The first record of the little known stomatopod Parasquilla ferussaci (Roux, 1828) in the Adriatic Sea is documented. One specimen was captured near islet Blitvenica in the eastern Adriatic (Croatian coast) on 26 January 2021 with a bottom trawl. This record indicates the extension of the known distributional range of this species in the Mediterranean Sea. Here we also provide the first data on the molecular identification of Parasquilla ferussaci supported by the detailed morphological description of the investigated specimen. Parasquilla is derived as a sister group to Faughnia , which together are sister to the genus Pseudosquillopsis .

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020-2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).

This work presents refined, updated subregional and regional non-indigenous species (NIS) inventories for the Mediterranean Sea, validated by national and taxonomic experts, with species records observed until December 2020. These datasets will be used as the baselines for the implementation of the Integrated Monitoring and Assessment Programme for the Mediterranean (IMAP) and the Mediterranean Quality Status Report 2023. In total, 1006 non-indigenous species have been found in Mediterranean marine and brackish waters. The highest numbers of NIS were observed in Israel, Türkiye, Lebanon and Italy. Approximately 45 species were categorized as data deficient, either due to lack of consensus on their alien status or the validity of their identification. Polychaeta, Foraminifera and macroalgae were the groups with the highest numbers of controversial species. There was a general increase in the yearly rate of new NIS introductions after the late 1990s, which appears to be slowing down in the last decade, but this may be confounded by reporting lags and differential research efforts. Between 1970 and 2020 there has been a steep increase in the proportion of shared species present throughout all four Mediterranean subregions, which are predominantly transported via shipping and recreational boating. While Lessepsian species are gradually spreading westwards and northwards, there is still a considerable invasion debt accumulating in the eastern and central Mediterranean.

The angular rough shark, Oxynotus centrina (Linnaeus, 1758), is a poorly known and rare bathydemersal shark inhabiting continental shelves and upper slopes with a significant lack of data and rarely published records in the Adriatic Sea in this century. In this paper, we present 20 new occurrences recorded from May 2015 to September 2021, of which 19 are in Croatian and one in Montenegrin territorial waters. Records of juveniles, subadults and adults are reported. Higher number of records off the Kornati archipelago in the central Adriatic Sea suggest that this area is of particular importance for this species. Furthermore, habitats in the Southern Adriatic might have lower density. Due to the nonsystematic research and nonprobabilistic data collection, it is difficult to establish whether the greater number of records in the continental shelf is just an ostensible phenomenon.

This Collective Article presents information on 20 taxa belonging to five (5) Phyla: Cnidaria (2), Mollusca (8), Arthropoda (4), Echinodermata (1) and Chordata (5) recorded from the Alboran Sea to the Levantine Sea. These new records were found in seven (7) different ecoregions as follows: Alboran Sea: new record of the rare football octopus Ocythoe tuberculata in the harbour of Algeciras (Spain); Western Mediterranean Sea: first record of the isopod Arcturinella deltensis in the Ligurian Sea, and the third in the whole Mediterranean Sea; third Mediterranean site for the Muricidae Coralliophila ahuiri along the Italian coasts (Alghero); first and westernmost record of the goby Corcyrogobius liechtensteini from the Iberian Peninsula; new record of the sea slug Glaucus atlanticus from the coast of the Iberian Peninsula; first and easternmost record of Holothuria (Vaneyothuria) lentiginosa lentiginosa along the Italian coasts; Tunisian Plateau/Gulf of Sidra: seventh record of the oceanic squid Thysanoteuthis rhombus in Tunisia, and first for the Gulf of Gabes. Ionian Sea: second occurrence of the Atlantic tripletail Lobotes surinamensis in the Ionian Sea and first record from the Strait of Messina area; new record of the rare sea elephant Pterotrachea coronata from the Strait of Messina; Adriatic Sea: first record of a facies of football ascidian Diazona violacea in the South Adriatic Sea (Tremiti Island, Italy); two records of the sevengill shark Heptranchias perlo in Croatian waters after more than 70 years of absence of documented records in this area; first known occurrence of the nudibranch Jalonus hyalinus in Slovenian waters and also the first known occurrence of this species in the Adriatic Sea; first record of the nudibranch Okenia elegans in Slovenian waters; Aegean Sea: First record of the parasitic isopod Nerocila milesensis along Greek coasts (Crete island) as well as the second record worldwide; additional record of the brachyuran Paragalene longicrura collected from the Saronikos Gulf (Greece); first record of the siphonophore Rhizophysa filiformis in Greek waters as well as the second record of this species in the eastern Mediterranean basin; new record of the rare and protected angelshark Squatina aculeata along Turkish coasts; Levantine Sea: first record of the marine amphipod Caprella andreae in the Levantine Mediterranean shore of Israel, based on both morphological and molecular data; first occurrence of the cephalopod Tremoctopus violaceus along Turkish coasts, which confirms its presence in the north-eastern coasts of Turkey; record of a bloom of the thermophilic jellyfish Pelagia noctiluca in the north Levantine Sea.