Small pelagic fish assemblages in relation to environmental regimes in the Central Mediterranean

The complex interactions between surface circulation and coastal and continental shelf morphology, as well as the presence of temperature and salinity gradients, make the Central Mediterranean an area characterized by high degree of ecosystem patchiness. The well-known effect of the physical environment in shaping community structure leads us to hypothesize the presence of differences in the pelagic fish community organization. Based on the analysis of specific environmental factors, nine sectors were identified and possible differences in the relative proportions of some key pelagic species were assessed by analysing the acoustic data collected during two surveys carried out in the summer period. The obtained results evidenced a clear separation between the northern (Strait of Sicily) and southern parts (Tunisian waters) of the study area, highlighting the strong effect of temperature on the proportions of some species. Furthermore, even if most of the variability in fish assemblages was due to the differences between the northern and southern parts, specific spatially nested differences were identified, highlighting a kind of hierarchical structure in the pelagic habitat, definitely allowing fish species to find their optimum in a high variable ecosystem, thus improving the system's resilience.