Spatio-temporal assessment of nearshore fish communities in a temperate estuary using functional and community metrics for restoration and management.

Understanding the structure and function of estuarine fish communities is essential for guiding ecosystem-based management and restoration. This study investigated long-term patterns in fish community composition, abundance, species richness and estuarine use across 15 nearshore sites within three estuaries and the Isle of Wight, located in the Solent, a large temperate estuarine system in southern England. Using a 12-year dataset (2007-2018) of biannual seine net surveys, we applied traditional community metrics alongside functional guild classifications and Fish Estuarine Association Scores (FEAS) to assess spatio-temporal variation and estuarine dependency. A total of 55 species were recorded, with six species (Atherina presbyter, Dicentrarchus labrax, Pomatoschistus microps and Chelon auratus and the family Clupeidae) accounting for 96% of individuals. Marine migrants and estuarine residents dominated the assemblage, indicating strong connectivity between estuarine and coastal habitats. While fish abundance declined significantly over time, species richness and community composition varied across seasons, tidal states and spatial scales. Sites and catchments differed markedly in FEAS, with some areas supporting species more dependent on estuarine habitats. These results highlight the importance of multisite, seasonal monitoring and the value of trait-based metrics in identifying nursery habitats and guiding restoration. The FEAS approach, applied retrospectively to historical data, offers a practical framework for setting ecological baselines and prioritising functionally important estuarine areas under real-world monitoring constraints.