Toxic Phytoplankton in Mussel Farms in the Gulf of Trieste, Adriatic Sea (Italy): A Preliminary Analysis of Long-Term Data (2001–2022) in Relation to Environmental Conditions

The present study utilised a comprehensive, long-term dataset of toxic phytoplankton (2001–2022) to analyse the relationships between the abundance, distribution, and seasonal trends of toxic phytoplankton, as well as the influence of various sampling methods, physico-chemical parameters, nutrients, and meteo-climatic parameters. The data were obtained through institutional monitoring at four selected sites dedicated to shellfish farming in the Gulf of Trieste (Adriatic Sea, Italy). The results show significant gradients in the spatial distribution of toxic phytoplankton and clear seasonal patterns in regard to the physico-chemical parameters and nutrients. Toxic phytoplankton abundance peaked in late winter/early spring and early autumn, depending on the genus considered. Significant correlations suggest that rainfall influences the nutrient levels and the proliferation of toxic phytoplankton. The time series analysis highlighted significant increases in temperature, salinity, and nitrogen species, during the study period, and decreases in silicon and phosphorous, while chlorophyll a and the overall phytoplankton abundance remained relatively stable, except for a significant decrease in Lingulodinium from 2015 to 2022. This preliminary assessment provides a valuable basis for further approaches (e.g., continuous in situ measurements, modelling, machine learning) to investigate the potential impact of climate variability on toxic phytoplankton dynamics in the Gulf of Trieste and to support mussel-farming management from both health and environmental perspectives.