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Annual and interannual dynamics of shellfish toxins and associated harmful algal species (HAS) were analyzed from 2015 to 2020 in Tortolì Lagoon (Sardinia, west Mediterranean Sea). Analysis of seasonal occurrence of different harmful algae, such as Dinophysis spp., Prorocentrum spp., Pseudo-nitzschia spp. and Alexandrium minutum, was performed. The species Dinophysis acuminata and Dinophysis sacculus were responsible for the accumulation of lipophilic toxins belonging to the okadaic acid group (OAs) and pectenotoxins2 (PTX2) in bivalve mollusks. The highest HAS detection was recorded in the winter months, in particular, Dinophysis spp. was mostly present in January–February. Out of 1090 analyzed mollusk samples, 39 were non-compliant, exceeding the legal limits (160 μg OA eq/kg e.p.) reported in Regulation 853/2004 of the European Commission. A statistical analysis related to the presence of OA and PTX2 in mollusks with various environmental parameters (pH, water temperature, dissolved oxygen, algal density) was implemented, proving a clear winter seasonality. The present study highlights the necessity to better understand the different factors able to influence the production and accumulation of toxins in bivalve mollusks bred in an important Sardinian production area. The contribution of this research is important not only from an environmental and productive point of view but also from the view of implementing management in order to mitigate any harm to human health.

Several planktonic dinoflagellates canproduce lipophilic phycotoxins that representa significant threat to public health aswell as to shellfish and fish farming.Poisoning related to some of these toxins iscategorised as diarrhetic shellfish poisoning.We analysed 975 shellfish samplesfrom Tortolì in the central-eastern region ofSardinia (Italy) from January 2016 toMarch 2020, to investigate the prevalenceof different lipophilic marine biotoxins inmollusc bivalves. The results highlightedthe predominant presence of toxins belongingto the okadaic acid group in all sampleswith toxin concentrations exceeding legallimits, and revealed the new occurrence ofpectenotoxins in oysters and clams with awinter seasonality in recent years. The originof shellfish toxicity was associated with the same Dinophysis species, mainly D.acuminata. Based on both these results andother precedents, monitoring and recording systems are strongly recommended.