Seasonal variation and seagrass cover: Influences on mobile marine fauna communities in NW Iberia

Seagrass ecosystems support marine biodiversity and ecosystem functioning in coastal areas. This study investigates the taxonomic and functional diversity, as well as community composition of invertebrates and fish within Zostera marina meadows along the Galician coast in NW Iberia, with a specific focus on variations across different seagrass covers and seasons. Utilising 360º Baited Remote Underwater Video Stations, comprehensive surveys were conducted across two seasons, summer and fall, to explore the interplay between species-habitat relationships and seasonal variations. Significant disparities in community structure and diversity were uncovered across various seagrass cover densities and the two seasons, highlighting the dynamic nature of these ecosystems. Fish species, notably smaller and gregarious ones like Atherina presbyter and Pomatoschistus flavescens , exhibited higher abundances in denser areas of the seagrass meadow, with noticeable seasonal fluctuations. Conversely, larger species,often solitary, exhibited spatial and temporal variability linked to sparse seagrass areas, highlighting the complexity of seagrass-associated communities. Functional structure analysis revealed significant differences in functional diversity across seasons and seagrass cover, emphasising the role of habitat complexity and seasonal variation in shaping mobile marine fauna communities. Specifically, communities in sparse areas exhibited higher functional diversity and reduced resource competition, while denser areas harboured species with similar functional traits competing for the same resources. Despite their ecological significance, seagrass meadows face significant anthropogenic pressures, including shellfishing activities, resulting in habitat alterations and degradation. The study underscores the importance of tailored conservation measures for these critical habitats, particularly in areas subjected to intense fishing pressure and habitat degradation. Integrated management approaches are necessary to preserve these invaluable ecosystems and ensure long-term sustainability. This study provides valuable insights into the spatiotemporal (throughout seasons and seagrass cover) variability of mobile fauna assemblages in a Zostera meadow and highlights the need for proactive conservation efforts to protect these vital coastal habitats.