Long-Term Variability in European Flat Oyster (Ostrea edulis Linnaeus, 1758) Larval Supply in Mali Ston Bay: Implications for Natural Spat Collection

Natural spat collection supports cultivation of the European flat oyster, Ostrea edulis, in Mali Ston Bay, but the availability of planktonic larvae varies markedly. We reviewed the development of local monitoring since 1971 and analysed larval observations from 2000–2024, focusing on interannual, seasonal and spatial variability, practical indicators for collector deployment, and concurrent temperature and salinity. The May–October dataset comprised 1734 station-date observations from 17 monitoring years. Larval abundance varied substantially among years, and although June generally showed higher abundance than July, the month of maximum abundance differed among years. The stations recording the highest larval concentrations also changed among monitoring periods. These patterns indicate that larval supply is temporally and spatially heterogeneous rather than characterized by a fixed seasonal peak or consistently dominant site. Associations with temperature were exploratory, and changes in sampling coverage and equipment preclude estimation of a quantified long-term trend. Repeated, site-specific monitoring can therefore inform the timing of collector deployment, while planktonic larval abundance alone cannot predict settlement or subsequent recruitment.