Sandy bottoms play a key role in shaping coastal fish functional β-diversity in the Mediterranean Sea

The functional diversity of temperate coastal ecosystems is strongly influenced by environmental variability and habitat characteristics. The specific contribution of different marine habitats to the functional diversity of fish communities remains comparatively understudied in temperate regions such as the Mediterranean Sea. Herein, we use a multivariate approach along with functional diversity indices to examine and compare the functional diversity and traits of fish communities in the three most abundant infralittoral Mediterranean habitats, sandy bottoms, rocky bottoms, and Posidonia oceanica meadows. The results revealed significant differences in functional diversity and traits among habitats, with variations in the ecological characteristics of fish communities. Specifically, functional traits such as the minimum depth and vertical distribution exhibited strong associations with particular habitats, influencing the functional structure of fish communities. Environmental drivers such as seabed temperature, depth, and chlorophyll concentration significantly influenced the functional composition of fish communities, as identified by partial redundancy analysis (pRDA). Among these, seabed temperature and depth explained the largest share of variation. No difference in functional redundancy was detected among habitats. Functional diversity is unevenly distributed across habitats, underscoring the significance of sandy bottoms in preserving functional beta diversity—an aspect often underrepresented in current conservation strategies. This study offers novel insights valuable for coastal biodiversity management, emphasising the complementary role of habitats in maintaining the ecological functionality of Mediterranean fish communities.