Climate change and shellfish farming contamination by marine biotoxins: new insights on toxic DSP (diarrhetic shellfish poisoning) events for a sustainable and safe production management of marine aquaculture.

Shellfish farming is an important activity along the Adriatic coast both in terms of food production and economic value. The impact of Harmful Algal Blooms events, even when they don’t directly cause an impact on human health, causes economic stress on this sector. In particular, events related to Diarrhetic Shellfish Poisoning (DSP) are the main ones responsible for the suspension of the harvesting activity in this basin. They are caused by species belonging to the Dinophysis genera, which presents peculiarities such as mixotrophic feeding, which makes the investigation of its ecological characteristics more complex than those of simple autotrophic species, and the ability to cause toxicity events even at low cell densities (10^2-10^3 cells/L). In fact, they usually represent a negligible percentage of the entire phytoplankton assemblage. During these three years as a Ph.D. student, an applied approach was used with the aim of increasing the knowledge and providing insights and tools for safer aquaculture production, in relation to DSP events in the Adriatic Sea. In the first chapter of the thesis, I analysed a 26-year long time series of Dinophysis and toxicity monitoring data, aiming to define the ecological dynamics of toxic Dinophysis species assemblages in relation to the toxicity events. A marked seasonality of Dinophysis species and toxicity events was highlighted, together with an association of D. fortii, D. caudata and D.tripos with toxicity events and the optimum temperature for maximum growth of some of the Dinophysis species; moreover, declining trends of declining trends observed in Dinophysis related phenomena are discussed in relation to the chemical and chlorophyll a decreasing trends. Lastly, some anomalies in the temperature and salinity conditions are discussed as they characterized periods with prolonged toxicity events. In the second chapter, a molecular assay based on qPCR was developed and applied to follow Dinophysis spp. occurrence over one year. The aim was to evaluate the use of this new assay as an early warning tool for the occurrence of toxic phytoplankton species in the coastal waters near shellfish farms in the Northwestern Adriatic Sea. Data obtained were compared with the official microscopy counts, demonstrating the potential of qPCR as a valuable method for monitoring Dinophysis species. The rapidity and sensitivity of the method, even at low abundance, renders it potentially useful for the early detection of HAB events, even for species with low densities.