A review of fish diversity in Mediterranean seagrass habitats, with a focus on functional traits

Seagrass habitats are considered essential in supporting both fish diversity and fisheries income. Within the Mediterranean Sea most fish species are associated to seagrasses and constitute the subject of extensive literature. However, a complete synthesis of fish species observed in different seagrass habitats is still lacking at the whole-basin Mediterranean scale, so hindering a thorough understanding of the main functional traits and mechanisms involved in determining fish diversity patterns. We performed a systematic review by implementing a semi-automated, threshold-based filtering pipeline that allowed building up a dataset concerning all fish species reported in native Mediterranean seagrasses, including specific functional traits known to be involved with the potential use of seagrasses by fish. These data allowed to carry on a narrative synthesis on fish diversity in seagrass habitats. Moreover, the functional traits analysis highlighted a significant role of trophic level, size and benthic domain in determining the distribution of fish in different seagrass habitats at whole Mediterranean basin scale. Data evidenced a pattern of segregation between large piscivorous, pelagic predators and smaller benthic prey (including juveniles) with omnivorous to herbivorous feeding habit, with aggressive predators significantly associated with Posidonia oceanica and Cymodocea nodosa beds while their putative prey tend to occupy other seagrass habitats. We identified unexpected knowledge gaps on the role of habitat heterogeneity and fish life stages in determining the presence/absence of fish in different seagrasses, for which in-depth research is needed to fully understand the links between nursery habitats and the state of exploited fish stock.