Trophic niche of an expanding pelagic fish species in the Mediterranean Sea

Abstract

Global change has been recognized as the main driver of the expansion of species outside to their native range, posing an important modification in the ecosystems through their potential effects on native biodiversity and community structure and functioning. Although a variety of factors may influence expansion success, how expanding species manage trophic resources may be the most critical factor to ensure survival and reproduction and one of the most important ways to impact native communities. Two main trophic pathways have been suggested to explain resource acquisition by expanding species: expanding species may behave aggressively over the resources exploited by natives, displacing them from their niches, or they may exploit niche opportunities that most native species are unable to use efficiently. The recent expansion in the Mediterranean Sea by the round sardinella Sardinella aurita, a tropical pelagic fish, as a consequence of the increase in the temperature of the Mediterranean waters provides an excellent field-laboratory to investigate the trophic strategies of marine species in expansion, as well as to quantify the trophic impact of these new species on populations and communities of ecological similar native species. We examined the main trophic pathways of the round sardinella and the trophic relationships with other ecological similar pelagic fish species in the North-Western Mediterranean Sea by analysing their stable isotopic values throughout the year. Results revealed that round sardinella overlapped its trophic niche with medium pelagic species (Atlantic horse mackerel Trachurus trachurus and Atlantic chub Scomber colias). Isotopic mixing models indicate that round sardinella is acting as a predator of small pelagic species (European anchovy Engraulis encrasicolus and sardine Sardina pilchardus). These results have clear implications to understand the ecological role of the round sardinella in the Mediterranean Sea