Biotoxins profile in mussels of the north-western Adriatic Sea in the last decade (2012-2022): major contamination events and correlation with toxic phytoplankton

The north-western Adriatic Sea (above 43° N) is one of the most eutrophic areas of the Mediterranean Sea and represents an important aquaculture area, accounting for about 90% of the Italian shellfish production. Since the 1970s, HAB species have frequently occurred in this area, posing a serious health risk to consumers. Therefore, according to European legislation, seawater and shellfish in production and relaying sites are regularly monitored. This study presents an analysis of over 2000 samples collected from 2012 to 2022 as part of the official monitoring in ten production sites along the coast of the Emilia-Romagna region. During this decade, no PSP toxins were above the regulatory limit in mussels, despite the presence of Alexandrium spp. in seawater. Instead, several toxic events related to lipophilic toxins occurred, with a clear correspondence between the main phytoplanktonic species involved in the production of each toxin and the toxin presence in mussels. Yessotoxins were detected in mussels predominantly during the autumn and winter seasons from 2012 to 2015, exceeding the regulatory limit by a significant margin. Different toxin profiles related with the presence of the producing species Gonyaulax spinifera, Lingulaulax polyedra, and Protoceratium reticulatum have been observed. Diarrhoeic toxins levels increased in mussels together with the increase in cell density of several Dinophysis spp. in seawater, for which seasonal trends were observed. Multiple toxic events attributable to these toxins have been identified, each resulting in the temporary closure of shellfish production sites.