The bloom-forming toxic dinoflagellate Alexandrium catenella was first detected in Southern Chile (39.5–55°S) 50 years ago and is responsible for most of the area’s cases of paralytic shellfish poisoning (PSP). Given the complex life history of A. catenella, which includes benthic sexual cysts, in this study we examined the potential link between latitude, toxicity, and sexual compatibility. Nine clones isolated from Chilean Patagonia were used in self- and out-crosses in all possible combinations (n=45). The effect of latitude on toxicity, reproductive success indexes, and cyst production was also determined. Although the toxin profiles were similar for all strains, consisting of C1, C2, GTX4, GTX1, GTX3, and NeoSTX, a latitudinal gradient was determined for their proportions (%) and content per cell (pg cell⁻¹), with the more toxic strains occurring in the north (−40.6°S). Reproductive success also showed a latitudinal tendency and was lower in the north. None of the self-crosses yielded resting cysts. Rather, the production of resting cysts was highest in pairings of clones separated by distances of 1000–1650km. Our results contribute to a better understanding of PSP outbreaks in the region and demonstrate the importance of resting cysts in fueling new toxic events. They also provide additional evidence that the introduction of strains from neighboring regions is a cause for concern.

Pufferfish (Tetraodontidae) inhabiting the Mediterranean Sea can represent an emerging public health risk due to the possible accumulation of marine neurotoxins (TTXs and STXs) in their tissues. In this study, the presence of pufferfish species in the Strait of the Sicily (Lampedusa Island, Italy) was investigated using a Citizen Science (CS) approach involving local fishermen. A sub-group of specimens collected were sent to the National reference Laboratory on Marine Biotoxins for de-termining the presence of TTXs using a validated HILIC-MS/MS method on fish tissue. The STXs presence was also screened in some specimens. Overall, 56 specimens, identified as Sphoeroides pachygaster (Müller &Troschel, 1848) were collected. Data on specimen total length, body weight, fishing method, catch area (with relative depth temperature and salinity) were analyzed and compared with the S. pachygaster records reported in Guardone et al. (2018), which were appro-priately updated until 2022. All the analysed tissues were found to be negative for both TTXs and STXs. The key role of the CS in monitoring potentially toxic marine species was proved. Outcomes from this study, the first investigating the toxicity of S. pachygaster in Italian waters, may provide useful data for the proper assessment of this emerging risk