The fingerprint of functional strategies in Mediterranean seagrass fish assemblages

ABSTRACT In the Mediterranean Sea, fish assemblages associated with seagrasses host a relevant percentage of the total fish biodiversity. While the structural complexity, coverage and distribution of seagrasses are known to influence species richness and abundance, their effect on the functional composition of faunal assemblages is still unclear. Moreover, little is known about the relationships of fish specific feeding, behavioural and reproductive strategies with the potential use of this habitat during different life stages. We characterized the functional structure of fish assemblages in three main Mediterranean seagrasses, using specific functional traits known to be associated with the potential use of meadows (e.g., as nursery, refuge and/or foraging areas). We also hypothesized that given combinations of traits could be associated with the probability of species being observed on seagrasses during well-defined life stages, thereby linking different strategies to habitat use. Fish functional assemblages are non-random structured, independently of either seagrass, taxonomic composition or species diversity, suggesting a convergence in their functional structures. Mediterranean seagrasses host a core of functionally similar fish species characterized by r-like reproductive strategies and low-to-intermediate trophic levels, although differing in the range of traits exhibited by predator fauna. Moreover, unique combinations of traits are significantly associated with the likelihood of fish being observed on seagrass during specific life stages. Our findings reinforce the view that the predominant use of seagrasses by fish may be driven by a trade-off between different life-history and feeding strategies. As functional strategies are largely involved in the structuring of food webs and species recruitment, their characterization in seagrass-associated fish assemblages would enhance our understanding of the impact of multiple threats on marine biodiversity.