Abstract
Bacteria are an active and diverse component of pelagic communities. The identification of main factors governing microbial diversity and spatial distribution requires advanced mathematical ...analyses. Here, the bacterial community composition was analysed, along with a depth profile, in the open Adriatic Sea using amplicon sequencing of bacterial 16S rRNA and the Neural gas algorithm. The performed analysis classified the sample into four best matching units representing heterogenic patterns of the bacterial community composition. The observed parameters were more differentiated by depth than by area, with temperature and identified salinity as important environmental variables. The highest diversity was observed at the deep chlorophyll maximum, while bacterial abundance and production peaked in the upper layers. The most of the identified genera belonged to Proteobacteria, with uncultured AEGEAN-169 and SAR116 lineages being dominant Alphaproteobacteria, and OM60 (NOR5) and SAR86 being dominant Gammaproteobacteria. Marine
Synechococcus
and
Cyanobium
-related species were predominant in the shallow layer, while
Prochlorococcus
MIT 9313 formed a higher portion below 50 m depth. Bacteroidota were represented mostly by uncultured lineages (NS4, NS5 and NS9 marine lineages). In contrast, Actinobacteriota were dominated by a candidatus genus
Ca.
Actinomarina. A large contribution of Nitrospinae was evident at the deepest investigated layer. Our results document that neural network analysis of environmental data may provide a novel insight into factors affecting picoplankton in the open sea environment.
Coccolithophores are unicellular marine algae belonging to the haptophyte group, characterized by the production of intricate calcium carbonate plates that adorn their cells and exhibit ...species-specific morphology. The Adriatic Sea has historically been the type locality of numerous phytoplankton species, including coccolithophores. However, since the initial description, many species have not been recorded during the frequent phytoplankton surveys in the Adriatic Sea. This was mainly because these surveys did not use electron microscopy, which is necessary for accurate species identification. In this study, we re-evaluate the coccolithophore species lists using historical records and compare them with recent surveys in the coastal and open waters of the Adriatic Sea. In light of changes in nomenclature resulting from clarification of the species’ life cycles, we update the taxonomic list of coccolithophore species occurring in the Adriatic.
Considering the role of phytoplankton in the functioning and health of marine systems, it is important to characterize its responses to a changing environment. The central Adriatic Sea, as a ...generally oligotrophic area, is a suitable environment to distinguish between regular fluctuations in phytoplankton and those caused by anthropogenic or climatic influences. This study provides a long-term perspective of phytoplankton assemblage in the central eastern Adriatic Sea, with 14 years of continuous time series data collected at two coastal and two offshore stations. The predominant phytoplankton groups were diatoms and phytoflagellates, but their proportion varied depending on the vicinity of the coast, as evidenced also by the distribution of chlorophyll a. In the coastal environment, the phytoplankton biomass was substantially higher, with a higher proportion of microphytoplankton, while small phytoplankton accounted for the majority of biomass in the offshore area. In addition, a decreasing trend in diatom abundance was observed in the coastal waters, while such trend was not so evident in the offshore area. Using a neural gas algorithm, five clusters were defined based on the contribution of the major groups. The observed increase in diversity, especially in dinoflagellates, which outnumber diatom taxa, could be a possible adaptation of dinoflagellates to the increased natural solar radiation in summer and the increased sea surface temperature.
In September 2015, a massive occurrence of the
species was recorded in central Adriatic Kaštela Bay. In order to taxonomically identify the
species responsible for this event and determine their ...toxin profile, cells collected in seawater and from benthic macroalgae were analyzed. Conservative taxonomic methods (light microscopy and SEM) and molecular methods (PCR-based assay) allowed the identification of the species
cf.
associated with
. The abundance of
cf.
reached 2.9 × 10
cells L
in seawater, while on macroalgae, it was estimated to be up to 2.67 × 10
cells g
of macroalgae fresh weight and 14.4 × 10
cells g
of macroalgae dry weight. An indirect sandwich immunoenzymatic assay (ELISA) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) were used to determine the toxin profile. The ELISA assay revealed the presence of 5.6 pg palytoxin (PLTX) equivalents per
cf.
cell. LC-HRMS was used for further characterization of the toxin profile, which showed that there were 6.3 pg of the sum of ovatoxins (OVTXs) and isobaric PLTX per
cf.
cell, with a prevalence of OVTXs (6.2 pg cell
), while the isobaric PLTX concentration was very low (0.1 pg cell
). Among OVTXs, the highest concentration was recorded for OVTX-a (3.6 pg cell
), followed by OVTX-b (1.3 pg cell
), OVTX-d (1.1 pg cell
), and OVTX-c (0.2 pg cell
).
This is the first study that presents concentrations of domoic acid detected in the whole shellfish tissue from breeding and harvesting areas along the Croatian coast of the Adriatic Sea during the ...period 2006 to 2008. Shellfish sample analyses after SAX cleaning procedures, using a UV-DAD-HPLC system, showed the presence of domoic acid in four species. The most prevalent of those species were the blue mussel (Mytilus galloprovincialis), followed by European flat oyster (Ostrea edulis), Mediterranean scallop (Pecten jacobaeus) and proteus scallop (Flexopecten proteus). Domoic acid, a potentially lethal phycotoxin that causes amnesic shellfish poisoning (ASP), was detected for the first time in January 2006 with the highest value of 6.5486 μg g⁻¹ in whole shellfish tissue. Pseudo-nitzschia spp. bloom events preceded these high domoic acid concentrations. According to this study, retention of domoic acid in the blue mussel M. galloprovincialis is more than 42 days. This investigation indicates the first presence of domoic acid in Croatian shellfish, but in concentrations under the regulatory limit (20 μg g⁻¹), therefore shellfish consumption was not found to endanger human health.
Marine diatoms of the genus Pseudo-nitzschia are widespread and occur in various environments. About half of the species described today have been shown to be toxic, producing the potent neurotoxin, ...domoic acid. The Pseudo-nitzschia species are a common component of the Adriatic phytoplankton community and are occasionally predominant. In the present study, the composition of the Pseudo-nitzschia species was studied in four distinct aquaculture areas from February 2022 to February 2023. These are the first results of a comprehensive study of Pseudo-nitzschia diversity combining morphological and molecular analyses. The integrated approach resulted in the confirmation of Pseudo-nitzschia brasiliana, Pseudo-nitzschia hasleana, Pseudo-nitzschia galaxiae, and Pseudo-nitzschia linea. The species, P. galaxiae, was the most frequently occurring, P. linea was found in all investigated areas, while P. hasleana and P. brasiliana were rare, and their distribution was limited mainly to Kaštela Bay. The findings of P. brasiliana and P. hasleana represent the first confirmation for the Adriatic Sea, while P. galaxiae and P. linea have not been previously reported along the eastern Adriatic coast.
SUMMARY
The aim of our research was to study the composition of Pseudo‐nitzschia species during a period when neurotoxin domoic acid (DA) was present in shellfish. Sampling was conducted in Kaštela ...Bay (Central Adriatic Sea), between November 2015 and January 2016. Concentrations of DA analyzed in various shellfish species were low, below the regulatory limit, while the highest abundance of Pseudo‐nitzschia spp. reached 1.85 × 105 cells L−1 in the surface layer, at the beginning of November. Within the temperature and salinity range recorded during the investigated period, a positive correlation of Pseudo‐nitzschia spp. abundance was recorded with temperature. Morphological analyses by scanning electron microscopy revealed the presence of five Pseudo‐nitzschia species that had already been reported in the Adriatic Sea – P. calliantha, P. delicatissima, P. fraudulenta, P. pseudodelicatissima
/P. cuspidata and P. subfraudulenta – as well as an unknown Pseudo‐nitzschia sp. The composition of the Pseudo‐nitzschia assemblage changed over the investigated period. The species P. pseudodelicatissima/P.cuspidata was found throughout the entire period and the highest diversity was noticed in January, when all six observed species were recorded. These results represent the first taxonomical investigation of the genus Pseudo‐nitzschia in Kaštela Bay, as well as the first report of DA in shellfish from this area.
The Krka River estuary is a karstic, permanently stratified estuary due to the strong freshwater inflow. It is a special environment in which to study the phytoplankton community, especially because ...this area is an important aquaculture site. Among other potentially toxic phytoplankton species, the diatom genus Pseudo-nitzschia occurs frequently and is a potential source of domoic acid (DA), causing shellfish toxicity and human intoxication. The main objective was to examine the dynamics of the phytoplankton community and, in particular, the genus Pseudo-nitzschia in the upper part of the Krka estuary, through monthly sampling over two years. The phytoplankton community was analysed using light microscopy and scanning electron microscopy to determine the diversity of Pseudo-nitzschia species and characterise the environmental parameters associated with a high abundance of Pseudo-nitzschia species. Seven Pseudo-nitzschia species were identified in the investigation, with higher frequencies and abundances in the less variable layer, at a 7 m depth. Blooms of Pseudo-nitzschia were noted in the late summer/early autumn, dominated by P. delicatissima/arenysensis. Winter assemblages were characterised by P. pseudodelicatissima/cuspidata, P. calliantha, and P. subfraudulenta, and were associated with domoic acid occurrence in shellfish.
Dinophysis spp. blooms and related shellfish toxicity events of diarrhetic shellfish poisoning (DSP) have been the most reported toxicity event through the Croatian National monitoring program. With ...the aim to characterize the DSP toxin profile in shellfish farmed in Croatia, for the first time a complete analysis of the toxin profile of Croatian mussels has been carried out using the LC-MS/MS technique. The obtained results showed okadaic acid (OA) as the main toxin contaminating Croatian mussels at that time. The maximum concentration of OA in shellfish tissue was recorded 12 days after the Dinophysis fortii bloom, thus suggesting that rapid growth of the toxin level in the shellfish occurred in the first week after the bloom while it was slower in the second week. Furthermore, the presence of only OA at concentrations which could endanger human health suggests D. fortii as the main organism responsible for the toxic event that occurred in Lim Bay. The presence of gymnodimine and spirolides in Croatian mussel has been detected for the first time, while the presence of yessotoxin and pectenotoxin-2 is confirmed.
The Mediterranean mussel, Mytilus galloprovincialis Lamarck, 1819 is a widely distributed commercially important bivalve species, and is one of two cultivated bivalve species in the Adriatic Sea, ...with the Krka River estuary being a key aquaculture location. Understating the feeding ecology of M. galloprovincialis could help aquaculture be more efficient. The aim of this study is to use stable isotopes to advance our understanding of M. galloprovincialis feeding ecology, as well as explore the potential of their shell as proxies for environmental change. We analyzed stable isotope composition (hereafter, δ13C and δ15N), of M. galloprovincialis soft tissue, as well as the δ15N signature of its shell, over one year at multiple sites in the Krka River estuary. Mussels showed differences in the isotopic niche depending on the site, indicating that feeding varies according to geographic location, likely due to specific conditions in the Krka River estuary and differences in food availability. During our entire survey period, marine organic carbon was the dominant source in the mussels cultivated in the Krka estuary. However, in the period from late summer to late autumn, the contribution of freshwater carbon sources increased for both sites situated in the middle estuary. The distinct feeding patterns observed at each sampling site could be attributed to a combination of factors such as local hydrographic conditions, food availability, and the presence of other competing species. Overall, the stable isotope results present valuable information on the feeding ecology of Mytilus galloprovincialis, highlighting the complex interactions between environmental factors and feeding habits. The results of our study contribute to the isotope data archive for M. galloprovincialis. Furthermore, this work shows the potential of M. galloprovincialis shell δ15N values as an indicator for nitrogen loading in aquaculture settings and coastal marine environments.
•Mytilus galloprovincialis in the Krka River estuary show spatial variation in feeding behaviour and carbon sources.•Krka River estuary offers a natural experimental design to explore spatial and temporal variability in shell geochemistry.•δ15NCBOM in Mytilus galloprovincialis shells has potential as proxies for environmental variations
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