Specific oceanographic conditions reflect meiofaunal communities: the case of a semi-enclosed gulf (Pagasitikos Gulf, Eastern Mediterranean)

Semi-enclosed gulfs exhibit distinct oceanographic conditions, influencing the inhabiting organisms and communities. Analyzing samples from 55 stations taken at 10 cm sediment depth in spring 2023 and belonging to three zones with different nutrient profiles, the meiofaunal communities in Pagasitikos gulf were examined, while their relationship with sediment properties , water chemistry and oceanographic conditions were investigated. Highest meiofaunal densities were observed in the internal gulf (458–1538 ind/10 cm 2 ) near the main urban area, with lowest reported for the upper external gulf (36–594 ind/10 cm 2 ). Two stations showed unusually high ciliate densities (454 and 598 ind/10 cm 2 ) that could not be explained by any of the examined parameters. Highest richness but lowest evenness, Shannon and Simpson indices were reported for the internal gulf, followed by the lower external gulf, while the upper external zone showed lowest values. Multivariate analyses showed that all three nutrient zones are associated with distinct meiofaunal communities, with depth and sand content being the most important factors influencing the meiofaunal communities, while also discussing the potential effect of anthropogenic activities . Total organic carbon did not explain differences in meiofaunal composition, stressing the need for more precise measurements. This study showcases that gulf-specific oceanographic conditions such as water and nutrient stratification and hydrodynamics can play a key role in shaping meiofaunal communities. • This is the first study on meiofauna of Pagasitikos Gulf, a semi-enclosed basin. • Depth and sand content influenced community structure and diversity patterns. • Nutrient availability and anthropogenic activities affect meiofaunal patterns. • Meiofauna of coastal systems are related to region-specific oceanographic regimes.