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Zooplankton plays a pivotal role in marine ecosystems and the characterisation of its biodiversity still represents a challenge for marine ecologists. In this study, mesozooplankton composition from 46 samples collected in summer along the western Adriatic Sea, was retrieved by DNA metabarcoding analysis. For the first time, the highly variable fragments of the mtDNA COI and the V9 region of 18S rRNA genes were used in a combined matrix to compile an inventory of mesozooplankton at basin scale. The number of sequences retrieved after quality filtering were 824,148 and 223,273 for COI and 18S (V9), respectively. The taxonomical assignment against reference sequences, using 95% (for COI) and 97% (for 18S) similarity thresholds, recovered 234 taxa. NMDS plots and cluster analysis divided coastal from offshore samples and the most representative species of these clusters were distributed according to the dominant surface current pattern of the Adriatic for the summer period. For selected sampling sites, mesozooplankton species were also identified under a stereo microscope providing insights on the strength and weakness of the two approaches. In addition, DNA metabarcoding was shown to be helpful for the monitoring of non-indigenous marine metazoans and spawning areas of commercial fish species. We defined pros and cons of applying this approach at basin scale and the benefits of combining the datasets from two genetic markers.

Food availability is thought to exert a bottom-up control on the population dynamics of small pelagic fish; therefore, studies on trophic ecology are essential to improve their management. Sardina pilchardus is one of the most important commercial species in the Adriatic Sea, yet there is little information on its diet in this area. Adult sardines were caught in the Gulf of Trieste (northern Adriatic) from spring 2006 to winter 2007. Experimental catches conducted over 24-h cycles in May, June and July showed that the sardines foraged mainly in the late afternoon. A total of 96 adult sardines were analysed: the number of prey varied from a minimum of 305 to a maximum of 3318 prey/stomach, with an overall mean of 1259 ± 884 prey/stomach. Prey items were identified to the lowest possible taxonomical level, counted and measured at the stereo-microscope. Overall, sardines fed on a wide range of planktonic organisms (87 prey items from 17 μm to 18.4 mm were identified), with copepods being the most abundant prey (56%) and phytoplankton never exceeding 10% of the prey. Copepods of the Clauso-Paracalanidae group and of the genus Oncaea were by far the most important prey. The carbon content of prey items was indirectly estimated from prey dry mass or body volume. Almost all carbon uptake relied on a few groups of zooplankton. Ivlev’s selectivity index showed that sardines positively selected small preys (small copepods < 1 mm size), but also larger preys (such as teleost eggs, decapod larvae and chaetognaths), confirming their adaptive feeding capacity.

Elasmobranch species are the direct or accidental catch of fisheries and can have a commercial importance. In the Mediterranean Sea, a long-term period of overfishing brought several demersal elasmobranchs to be depleted and threatened by extinction, due to vulnerability related to their life history traits. In such exploited species, information on genetic diversity and connectivity is lacking and should be collected to identify management units. In this study, we focused on two threatened smooth-hound species, Mustelus Mustelus (Linnaeus, 1758) and M. punctulatus (Risso, 1827), whose abundance and distribution showed a decline at the Mediterranean regional level in the last century. Thanks to an opportunistic yet extensive sampling, we obtained the largest subregional collection of specimens for genetic analysis so far. In total, 86 and 214 specimens of M. mustelus and M. punctulatus were collected between 2016 and 2020 in the Adriatic Sea and the Strait of Sicily. We assessed the population genetic structure typing 17 microsatellites and sequencing part of the mitochondrial control region in both species. We observed a substantial nuclear and mitochondrial genetic structure when accounting for the geographical sampling area for both species. Our results indicate the presence of at least two genetic stocks for each of the two species: one in the Strait of Sicily and the other in the Adriatic Sea. This study provides valuable data that should be integrated into a broader approach to define management units, improving the development of an effective management strategy for these threatened species in the Central Mediterranean Sea.

Anchovies represent the largest world’s marine fish catches and the current threats on their populations impose a sustainable exploitment based on sound scientific information. In the European anchovy ( Engraulis encrasicolus ), the existence of several populations has been proposed but a global view is missing. Using a multidisciplinary approach, here we assessed the divergence among different ecotypes and its possible causes. SNPs have revealed two functionally distinct ecotypes overlapping in the Central Mediterranean, with one ecotype confined near the river estuaries. The same SNPs outliers also segregated two distinct populations in the near Atlantic, despite their large spatial distance. In addition, while most studies suggested that adaptation to low salinity is key to divergence, here we show that the offshore ecotype has higher environmental tolerance and an opportunistic feeding behaviour, as assessed by the study of environmental conditions, anchovy diet and trophic levels, and passive egg dispersal. These results provide insights into the anchovy evolutionary history, stressing the importance of behaviour in shaping ecotypes.

Dvajsetega junija 2023 so ribici v trislojno mrezo ujeli primerek kostanjevke Brama brama (Bonnaterre, 1788) (Bramidae) na 5 m giobine v Trzaskem zalivu. B. brama je pelaska neriticna oceanodromna vrsta, ki se pojavlja povsod v zmernih in toplih morjih v globinskem razponu med 0 in 1000 m giobine, obcasno pa se pribliza obali. V vzhodnem Sredozemskem morju in jadranskem morju jo smatrajo za redko vrsto. Pricujoci zapis je najnovejsi v Trzaskem zalivu, so pa znani zgodovinski zapisi, katerih primerki so shranjeni V Trzaskem prirodoslovnem muzeju.

The recent northward expansion of the round sardinella Sardinella aurita in the Mediterranean Sea has been documented as a consequence of rising sea temperature. At the same time, declines in sardine and anchovy biomass have been observed in the NW Mediterranean Sea, necessitating an assessment of whether the expansion of round sardinella may affect sardine and anchovy populations. Here, we combined stomach content and isotopic analyses to describe the trophic habits of round sardinella in the NW Mediterranean Sea and its trophic relationships with 2 sympatric small pelagic fish, European anchovy Engraulis encrasicolus and European pilchard Sardina pilchardus. Results revealed changes in the diet of round sardinella during the year. In summer, the most important prey were copepods (Acartia spp.) and cladocerans (Penilia avirostris). During winter, the diet was composed mainly of copepods and tunicates (mainly appendicularians), but microplankton was also numerically important in adult diets. In contrast to previous studies, during spring, round sardinella principally fed on salps (Thaliacea). To our knowledge, this is the first time that salps have been identified as an important prey for round sardinella. When compared to coexisting small pelagic fish, we found that round sardinella adults had a different trophic niche than anchovy and sardine. In contrast, round sardinella juveniles partially overlapped the trophic niche with the juveniles of the other 2 species. Therefore, the range expansion of round sardinella probably would not affect sardine and anchovy populations. Only in a situation of food limitation could juveniles of round sardinella compete with and affect both sympatric species. Our results provide new insights into the ecological role of this range-expanding species in the NW Mediterranean Sea, and highlight the importance of gelatinous zooplankton as prey.

Historical baselines are needed to reconstruct long-term changes in marine animal populations and enhance our ability to articulate management recommendations. We reconstructed common angelshark (Squatina squatina) abundance in the Northern Adriatic Sea over the last two centuries by integrating different sources of formal and informal information. The wide amount of information collected helped assessing if the species is actually extirpated from the area, as stated in previous studies. According to naturalists’ accounts and historical documents, in the nineteenth and early twenty-first centuries the species was so abundant to sustain targeted fisheries, and large quantities of S. squatina were sold in the main fish markets. In the 1960s, the species collapsed and got economically extinct. Even if it was never caught in the area through scientific surveys during the period 1948–2014, from fishermen interviews emerged that the species is not extirpated. However, only 50% of interviewees caught S. squatina at least once and they were significantly older than the fishermen that never caught it (shifting baseline syndrome). Moreover, the size of the fish caught significantly decreased through time, indicating the depletion of larger individuals. Our integrated approach can be applied to any poorly assessed species so that appropriate international conservation measures can be prioritized.

In September 2021, as part of the Italian Arctic research programme, a multidisciplinary cruise along the 75th parallel north through the Greenland Sea Gyre was conducted aboard the Italian icebreaker Laura Bassi in the framework of the CASSANDRA project, which also contributed to the Synoptic Arctic Survey (SAS) 2020/22. The cruise took place during the period of the lowest summer sea ice extent ever measured. The data show strong horizontal gradients with temperatures between 1.5 and 9.0 °C and salinity between 30 and 35. Warm and salty Atlantic Water (AW, θ > 3.0 °C, S around 35) dominates on the eastern side of the transect in the upper 500 m with surface temperatures of 4.5–9.0 °C, while Polar Water (PW, θ < 0 °C, S < 33) occupies the surface layer (50–80 m) in the west. The intermediate layer (100–500 m) consists of mixed water, and below 500 m the deep water of the Greenland Sea and the Norwegian Sea predominates. The oxygen enrichment is higher in the intermediate layers, while the values in deep layers and western regions are lower (<300 µmol kg−1). A stratified upper layer (30–50 m deep) with low surface nutrients, especially nitrate, is observed, while an accumulation of silicate occurs in deep water masses. The surface water in the eastern part of the transect has high pHT and total alkalinity values due to photosynthesis and the presence of salty AW, while the fresh PW in the west has a lower alkalinity. Respiratory activity and organic matter concentrations (particulate/dissolved organic carbon) vary horizontally at the surface, decrease with depth, and increase slightly near the seafloor. A west–east gradient is also observed for δ18O and δD, with the ratios indicating the influence of freshwater at the surface near the Greenland coast. The abundance of prokaryotes decreases from the photic zone (<100 m depth) to the sea floor. Carbohydrates and carboxylic acids are identified as well-utilised polymers at every station and in every layer. Overall, the microbial enzyme patterns show a decrease from the surface to deeper layers, with some hotspots of metabolic activity at 20–40 m and in the aphotic layer. The enzyme patterns vary spatially, with activity peaks at the ends and in the middle of the transect. Phytoplankton biomass, expressed as chlorophyll a, varies across the transect, with higher values at the westernmost and easternmost stations. The micro-phytoplankton fraction dominates in PW, while the nano-phytoplankton fraction predominates in AW, even at the interface between the two water masses. Data of phytoplankton communities show low abundances and a dominance of nano-sized organisms, with diatoms being more abundant in the western part. Microzooplankton represents an important fraction of the planktonic community in this area, with tintinnids being the most important groups along the transect. Micrometazoans and aloricate ciliates are more abundant in the AW, resulting in higher biomass values at the eastern stations. Copepods are the most abundant mesozooplanktonic taxon both at the surface and in the upper 100 m water layer (97 % and 94 % of total mesozooplankton abundance, respectively), mainly represented by the genus Calanus. The data are publicly available at the Italian Arctic Data Centre (IADC), see https://doi.org/10.71761/c082c3ca-40bf-42b1-a61a-7b3697ab2c5a (Bensi et al., 2024), https://doi.org/10.71761/f7474404-3331-43e5-883b-25755e94956d (Azzaro et al., 2024).

Historical baselines are needed to reconstruct long-term changes in marine animal populations and enhance our ability to articulate management recommendations. We reconstructed common angelshark (Squatina squatina) abundance in the Northern Adriatic Sea over the last two centuries by integrating different sources of formal and informal information. The wide amount of information collected helped assessing if the species is actually extirpated from the area, as stated in previous studies. According to naturalists' accounts and historical documents, in the nineteenth and early twenty-first centuries the species was so abundant to sustain targeted fisheries, and large quantities of S. squatina were sold in the main fish markets. In the 1960s, the species collapsed and got economically extinct. Even if it was never caught in the area through scientific surveys during the period 1948-2014, from fishermen interviews emerged that the species is not extirpated. However, only 50% of interviewees caught S. squatina at least once and they were significantly older than the fishermen that never caught it (shifting baseline syndrome). Moreover, the size of the fish caught significantly decreased through time, indicating the depletion of larger individuals. Our integrated approach can be applied to any poorly assessed species so that appropriate international conservation measures can be prioritized.