Analisi del reclutamento di molluschi bivalvi e specie associate lungo le coste dell'Istria, Croazia

The Mediterranean Sea, despite its relatively small size, hosts a huge biodiversity with more than 17 thousand species currently known. In this context, coastal areas, which are among the most productive marine ecosystems, hosts most of that biodiversity. Filter-feeding organisms such as bivalves plays a key ecological role, contributing to ecosystem functioning and providing suitable substrates for the settlement of other organisms. The pen shell Pinna nobilis is the largest bivalve in the Mediterranean Sea and acts as a keystone species. However, in 2016, mass mortalities events due to a bacterial infection started to spread across the basin killing more than 90% of Pinna nobilis populations in some areas. In the following years, many projects, like LIFE PINNA and LIFE PINNARCA, started across European countries to study the phenomenon and help the bivalve recover its populations. This study its part of the project “PinnAdriaNet”, started in 2020 in Croatia, which uses larval collectors to capture juveniles P. nobilis. The aim of this study is to analyse and compare the assemblages collected at different depth between two years, 2024 and 2025. The collectors were deployed along the Istrian coast, at the Bekarija site in the northern Adriatic Sea, for six months in 2024 and for five months in 2025. In 2025, a total of 45 taxa were identified, of which 16 were bivalves, including four individuals of juveniles Pinna sp. Higher species richness and heterogeneity were observed in 2025 compared with 2024, while, in both years, a proportionally greater evenness was observed at 12 m depth. These results confirm that collectors represent an effective tool for investigating reproductive and recruitment processes in the area, particularly bivalves. However, the recruitment of Pinna sp. remained low, although higher than in 2024, likely due to the reduced abundance of Pinna sp. populations still present in the area.