The pelagic food web of the Western Adriatic Sea: a focus on the role of small pelagics

Abstract

Abstract Small pelagic fishes play a crucial role in pelagic food webs as both top-down and bottom-up controllers. Their role as predators could also exert a wasp-waist flow control. The Adriatic basin is one of the largest areas of occurrence of small pelagic shared stocks and the most exploited basin of the Mediterranean Sea. Here, we analyzed the ontogenetic and spatial variations in the stable isotope composition of three small pelagic fishes (i.e., Engraulis encrasicolus, Sardina pilchardus, and Sprattus sprattus) collected throughout the western side of the basin and relate such differences to both resource availability and environmental variables. Medium-sized specimens of the three species mostly fed on small zooplankton, while adult sprats relied on large copepods and those of sardine and anchovy seemed to shift on phytoplankton, confirming the high trophic plasticity of these two dominants small pelagic species. Resource partitioning occurred at each size and in each sub-area, also favored by the high productivity and in turn high resource availability of the basin, especially in the northern part. These small pelagic fish were located at different, but very close, trophic position with other small pelagic species, and thus competition might occur in the future driven by modified feeding conditions as consequence of increasing sea temperatures.