Preliminary Study on the Occurrence of Saxitoxins in Marine Invertebrates from Apulia Lagoons

Saxitoxins (STXs) are potent neurotoxins associated with harmful algal blooms (HABs) and represent a major concern for seafood safety. While monitoring programs mainly target bivalve molluscs, information on STXs occurrence in other aquatic organisms remains limited. This study investigated STXs occurrence in marine invertebrates from the Lesina and Varano coastal lagoons (southern Italy) and its relationship with phytoplankton composition and environmental conditions. STXs were determined by enzyme-linked immunosorbent assay (ELISA) in the Pacific oyster (Magallana gigas), the Atlantic blue crab (Callinectes sapidus), and gelatinous zooplankton. Potentially STXs-producing dinoflagellates were mainly represented by Gymnodinium spp. and Alexandrium spp., including Alexandrium minutum. Temperature showed the strongest association with the genus Alexandrium, whereas Gymnodinium spp. was negatively associated with salinity, although these relationships were not statistically significant. STXs were detected in all investigated matrices at concentrations below the EU maximum level for bivalve molluscs, which was used only as a contextual reference. Among the investigated matrices, C. sapidus showed both the highest occurrence of STXs-positive samples and the highest toxin concentrations. Tissue-specific analyses revealed STXs in all analysed anatomical compartments, with the highest concentrations detected in the hepatopancreas. These findings suggest that STXs circulation may extend beyond traditional bivalve vectors and provide preliminary evidence supporting a multi-compartment approach for investigating toxin dynamics in Mediterranean transitional ecosystems.