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.