The Mediterranean fan mussel Pinna nobilis (L. 1758) has undergone since 2016 severe Mass Mortality Events (MMEs), leading to a drastic decline of the species throughout its entire range. The distribution and structure of Pinna nobilis remnant populations in the Venice Lagoon, one of the largest Mediterranean coastal transitional ecosystems, have been investigated through multiple approaches across different spatial and temporal scales.
Since 2020, the population in a study area near Ottagono Alberoni island (central Lagoon) has been monitored monthly, the frequence shifting to seasonal in 2024, when a second site characterized by a higher density of alive specimens, near Valgrande channel, was also included in the monitoring. Overall, the status of 556 individuals was assessed over time. The study areas were examined for the presence of main pathogens involved and for the physiological response of selected Pinna nobilis individuals. Temperature, salinity and dissolved oxygen were measured in continuous in the two areas. Hypoxic events recorded at the Ottagono Alberoni study area may help explain the differences observed in mortality rates between the two sites. Additionally, mortality is positively related to age, with younger individuals showing a relatively higher survival rate.
Moreover, an extensive sampling campaign was carried out in 2024 at 40 sampling stations over the whole lagoon in collaboration with Regione Veneto, in the framework of Interreg IT-SI POSEIDONE. Density, size structure and dead/alive status were determined for 2646 recorded individuals, and the overall status of the species in the lagoon was assessed. Despite the observed MMEs, the Venice Lagoon may still host one of the largest extant population of Pinna nobilis. Present results will also be discussed in relation to research perspectives, management policies and conservation strategies for the species.