Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast

A decade-long study on harmful dinoflagellate blooms and biotoxin contamination in mussels from the north-western Adriatic Sea (Mediterranean Sea)

The north-western Adriatic Sea is one of the most eutrophic areas of the Mediterranean Sea and an important aquaculture region, accounting for about 90% of Italian shellfish production. Since the 1970s, this area has experienced frequent harmful algal blooms, posing risks to consumers and coastal ecosystems. Despite the regular monitoring required by European legislation, long-term studies integrating taxonomic analysis of phytoplankton species, associated biotoxins, and environmental data remain limited. This study examines an 11-year dataset (2012-2022) from the Emilia-Romagna region coast, focusing on timing and occurrence trends of toxic dinoflagellates related to the shellfish toxicity. Phytoplankton species distribution and biotoxins content in farmed mussels were analysed, with particular attention to the presence of analogues. From 2012 to 2015, the most prevalent toxins were yessotoxins (YTXs, up to 8.44 mg kg-1), primarily homo-YTX and 45OH homo-YTX, which were associated with autumn blooms of Gonyaulax spinifera and Lingulaulax polyedra. From 2015, okadaic acids and derivatives (OAs, up to 941 µg kg-1) became the most prevalent phycotoxin group, associated to Dinophysis fortii and Dinophysis acuminata presence during autumn. This temporal shift was likely driven by increasing surface water temperature and salinity, which contributed to reduced water column mixing favouring oligotrophic species. Notably, low levels of YTXs persisted in mussels despite decreased abundances of producing species. Additionally, Alexandrium spp. cells were consistently detected, even in the absence of saxitoxins (STXs) in bivalves. These findings highlighted the need for integrated studies on strain-specific toxicity, phycotoxins accumulation in bivalves, and field monitoring.

Bio-tracking, bio-monitoring and bio-magnification interdisciplinary studies to assess cyanobacterial harmful algal blooms (cyanoHABs)' impact in complex coastal systems

Cyanobacterial Harmful Algal Blooms (cyanoHABs) represent significant threats to human health and environmental sustainability. These blooms, characterized by the rapid proliferation of toxic species, can release harmful toxins into aquatic environments, with severe consequences for ecosystems and human populations. Traditional research on cyanoHABs faces several limitations, including the lack of standardized detection methods, environmental variability, and low awareness of the associated risks. Most studies rely on conventional laboratory techniques, which are often resource-intensive and not widely accessible. Additionally, the complex dynamics of cyanoHABs, influenced by factors such as temperature, nutrients, and bloom evolution, make it difficult to establish consistent regulatory and monitoring frameworks. This paper presents a new integrated strategy that combines advanced technologies (remote sensing, in-situ multispectral analysis, mass spectrometry) with bio-monitoring and bio-tracking. This interdisciplinary approach improves the monitoring of cyanoHAB spread, tracks bioaccumulation in the food chain, and provides timely warnings for public health protection. The case study focuses on the Campi Flegrei area, an active volcanic region in Southern Italy, where Lake Avernus, a volcanic lake, has experienced periodic cyanobacterial blooms. This region also hosts mussel aquaculture and recreational activities. Remote sensing allowed the tracking of the 2022 bloom from the lake to the sea, reaching a mussel farm along the coast. Rapid detection and quantification of anabaenopeptins in bivalves enabled timely alerts to local authorities, prompting an assessment of contamination risks. The study demonstrates how the integration of remote sensing and molecular analysis enhances environmental monitoring by providing real-time, high-resolution data. This approach supports a better understanding of bloom dynamics, bioaccumulation, and impacts on the food chain, informing risk management and regulatory strategies. The research highlights the value of combining advanced technologies to improve the management of cyanoHAB-related risks, protecting both human health and ecosystem sustainability.

Shellfish farming contamination by marine biotoxins: New insights into the ecological toxic dinoflagellate Dinophysis dynamics and DSP (diarrhetic shellfish poisoning) events for safe production management of marine aquaculture

Mussel farming is a strategic economic activity for several coastal regions, where seawater and mussels are regularly monitored for the presence of the toxic dinoflagellate Dinophysis and associated toxins. This study analysed the ecological dynamics of Dinophysis species assemblages in relation to the toxicity events recorded in mussel farms and environmental variables over the multi-year (1998-2023) continuous observations along the Emilia-Romagna and Marche coasts (northwestern Adriatic Sea). DSP (diarrhetic shellfish poisoning) toxicity events were mainly recorded in autumn and winter and were associated with the abundance of D. caudata, D. fortii and D. tripos species (rs = 0.84, rs = 0.83, and rs = 0.66, respectively, p < 0.05). The Dinophysis species showed a clear seasonality with a succession of D. acuminata, D. sacculus in spring-summer, followed by D. caudata and finally D. fortii and D. tripos in autumn. In addition, each Dinophysis species showed its own optimum temperature for maximum growth. Furthermore, interannual trends showed an increase in Dinophysis spp. absence and a decrease in toxicity in bivalve mussels (5.35 and -3.31 % year-1, respectively), accompanied by a decreasing trend in DIN, phosphate and total phosphorus, and chlorophyll a (-1.97 %, -2.64 %, -3.3 % and -1.73 % year-1, respectively). In 2015 and 2022, prolonged toxicity events occurred when the surface waters were colder and slightly saltier than the long-term average. The data analysis highlighted the importance of the long-term observations for understanding the variability of DSP events and Dinophysis dynamics in relation to the environmental conditions to improve the management of aquaculture activities.

Mesodinium-Dinophysis encounters: temporal and spatial constraints on Dinophysis blooms

Species of the Dinophysis acuminata complex are the main cause of diarrhetic shellfish poisoning worldwide. These mixotrophs perform photosynthesis with plastids stolen from specific ciliate prey. Current transport models forecast advection of established populations, but modelling bloom development and maintenance also needs to consider the prey (Mesodinium spp.) of Dinophysis. Predator and prey have distinct niches, and Dinophysis bloom success relies on matching prey populations in time and place. During autumn 2019, red tides of Mesodinium rubrum in Reloncaví Fjord, Chile, were not followed by Dinophysis growth. The dynamics of Mesodinium-Dinophysis encounters during this and additional multiscale cases elsewhere are examined. Analogies with some classic predator-prey models (match-mismatch hypothesis; Lasker's stable ocean hypothesis) are explored. Preceding dense populations of Mesodinium do not guarantee Dinophysis blooms if spatial co-occurrence is not accompanied by water column structure, which leads to thin layer formation, as in Lasker's stable ocean hypothesis or if the predator growth season is over. Tracking the frequency of vacuolate Dinophysis cells, irrefutable signal of prey acquisition, with advanced in situ fluid-imaging instruments, is envisaged as a next-generation tool to predict rising Dinophysis populations.

Metabolic transformation of paralytic shellfish toxins in the mussel Mytilus galloprovincialis under different exposure modes

Gymnodinium catenatum is a widely distributed toxic marine dinoflagellate that produces paralytic shellfish toxins (PSTs). It is prone to causing algal blooms and poses a serious threat to the shellfish industry and human health. Previous studies have shown that when algal blooms occur, shellfish can accumulate PSTs in their bodies due to filtration. In this study, mussels (Mytilus galloprovincialis) were fed with G. catenatum at different fixed or varied cell density over time, with the latter designed to mimic the changes in algal cell density over time in the wild. The PST concentration in the mussels was positively correlated with the number of algal cells, and PSTs rapidly accumulated in the mussels under both feeding modes. Compared with constant feeding in the low feeding group, variable cell density feeding over time was more conducive to the accumulation of PSTs in M. galloprovincialis. An obvious toxin transformation process was also detected in the mussels, which transformed the less toxic gonyautoxins-5 and -6 and N-sulfocarbamoyl gonyautoxin-3 ingested from G. catenatum into the more toxic decarbamoyl gonyautoxin-2, decarbamoyl saxitoxin, and decarbamoyl neosaxitoxin. The ratio of epimer pairs, α:β, tended to stabilize when the toxin concentration was highest, and it increased rapidly after mussels stopped consuming toxigenic algae. These results suggested that the formation of α-stable toxoids mainly occurred during the process of toxin depuration. Toxins were also transformed from low to high toxicity, and α-stable toxoids were formed mainly in the hepatopancreas. These results provided basic data for better understanding of the laws governing metabolic transformation of PSTs in bivalves during algal blooms.

Nationwide seasonal monitoring of lipophilic marine algal toxins in shellfish and causative microalgae along the coasts of South Korea

In this study, lipophilic marine algal toxins (LMATs)-producing microalgae were identified at 23 sites along the coasts of Korea, and distribution characteristics of LMATs in phytoplankton and mussels were investigated. The causative microalgae, including Gonyaulux spinifera, Dinophysis acuminata, D. caudata, and D. fortii, were observed in the study area, with notably higher densities during the summer. Significant correlations were found between the densities of these microalgae and the water temperature. Seasonal distribution patterns of LMATs in phytoplankton closely matched those observed in mussels. Notably, LMAT concentrations in mussels from the Yellow Sea were relatively high. PTX2 was detected predominantly in phytoplankton, and homo-yessotoxin was found mainly in mussels. Overall, LMAT concentrations were elevated in the summer, raising concerns about biotoxin contamination in shellfish. These results provide important insights into the dynamics of unmanaged marine biotoxins in Korea and offer baseline data for future safety management policies and inflow surveillance.

Molecular monitoring of Dinophysis species assemblage in mussel farms in the Northwestern Adriatic Sea

Several Dinophysis species can produce potent lipophilic toxins that pose a risk to human health when contaminated seafood is consumed, especially filter-feeding bivalve mussels. In the mussel farms of the Northwestern Adriatic Sea, seawater and seafood are regularly monitored for the presence of Dinophysis species and their associated toxins, but the current methodological approaches, such as light microscopy determinations, require a long time to make results available to local authorities. A molecular qPCR-based assay can be used to quantify various toxic Dinophysis species in a shorter timeframe. However, this approach is not currently employed in official testing activities. In this study, field samples were collected monthly or bi-weekly over one year from various mussel farms along the Northwestern Adriatic coast. The abundance of Dinophysis species in the seawater was determined using both traditional microscopy and qPCR assays. In addition, the concentration of lipophilic toxins for DSP in mussel flesh was quantified using LC-MS/MS focusing on the okadaic acid group. Dinophysis spp. site-specific single cells were isolated and analysed by qPCR yielding a mean rDNA copy number per cell of 1.21 × 104 ± 1.81 × 103. The qPCR assay gave an efficiency of 98 % and detected up to 10 copies of the rDNA target gene. The qPCR and light microscopy determinations in environmental samples showed a significant positive correlation (Spearman rs = 0.57, p-value < 0.001) with a ratio of 2.24 between the two quantification methods, indicating that light microscopy estimates were generally 44.6 % lower than those obtained by the qPCR assay. The qPCR approach showed several advantages such as rapidity, sensitivity and efficiency over conventional microscopy analysis, showing its potential future role in phytoplankton monitoring under the Official Controls Regulations for shellfish.

Microbiological and Toxicological Investigations on Bivalve Molluscs Farmed in Sicily

Bivalves can concentrate biological and chemical pollutants, causing foodborne outbreaks whose occurrence is increasing, due to climatic and anthropic factors that are difficult to reverse, hence the need for improved surveillance. This study aimed to evaluate the hygienic qualities of bivalves sampled along the production and distribution chain in Sicily and collect useful data for consumer safety. Bacteriological and molecular analyses were performed on 254 samples of bivalves for the detection of enteropathogenic Vibrio, Arcobacter spp., Aeromonas spp., Salmonella spp., and beta-glucuronidase-positive Escherichia coli. A total of 96 out of 254 samples, collected in the production areas, were processed for algal biotoxins and heavy metals detection. Bacterial and algal contaminations were also assessed for 21 samples of water from aquaculture implants. Vibrio spp., Arcobacter spp., Aeromonas hydrophila, Salmonella spp., and Escherichia coli were detected in 106/254, 79/254, 12/254, 16/254, and 95/254 molluscs, respectively. A total of 10/96 bivalves tested positive for algal biotoxins, and metals were under the legal limit. V. alginolyticus, A. butzleri, and E. coli were detected in 5, 3, and 3 water samples, respectively. Alexandrium minutum, Dinophysis acuminata, Lingulodinium polyedra, and Pseudonitzschia spp. were detected in water samples collected with the biotoxin-containing molluscs. Traces of yessotoxins were detected in molluscs from water samples containing the corresponding producing algae. Despite the strict regulation by the European Commission over shellfish supply chain monitoring, our analyses highlighted the need for efficiency improvement.