Development and application of innovative tools for the monitoring of toxic phytoplankton in Italian bivalve mollusc farming areas

Marine coastal ecosystems are increasingly exposed to intense anthropogenic pressures and to the growing occurrence of Harmful Algal Blooms (HABs), which adversely affect biodiversity, ecosystem functioning, and public health. Within the European Union, monitoring frameworks for toxin-producing phytoplankton have been established for several decades; however, harmonised criteria for sampling frequency, threshold levels, and data interpretation remain incomplete. This PhD research aimed to improve the understanding of harmful phytoplankton dynamics and to support the development of science-based threshold values as early-warning tools for Italian coastal waters. The thesis integrates long-term ecological data analysis, laboratory method optimisation, and molecular diagnostics across two high-risk areas: the north-western Adriatic Sea and the Gulf of Oristano (Sardinia). Chapter 1, focused on the north-western Adriatic Sea, analyses an 11-year dataset correlating toxic dinoflagellates, phycotoxin accumulation in mussels, and environmental drivers, revealing a recurrent pattern of toxic events associated with rising sea surface temperatures and the dominance of specific harmful species. Chapter 2 establishes a reliable workflow for the extraction and quantification of Paralytic Shellfish Toxins (PSTs) from Alexandrium spp. biomass. The third and fourth chapters, centred on the Gulf of Oristano, investigate A. minutum bloom dynamics and the potential application of various molecular assays. Chapter 3 highlights the role of strain-level variability, environmental conditions, and interactions with co-occurring phytoplankton in shaping bloom toxicity, while Chapter 4 assess quantitative molecular approaches (qPCR, dPCR) for the rapid and accurate detection of A. minutum cells and other PSTs-producing species, demonstrating their potential integration into HAB monitoring as early-warning and decision-support tools. Overall, this work strengthens the scientific and methodological basis for HAB surveillance in Italy, contributing to the development of harmonised European monitoring guidelines. It also underlines the need for area- and species-specific approaches integrating molecular, chemical, ecological, and environmental data to enhance seafood safety and coastal management.