Effects of environmental conditions and jellyfish blooms on small pelagic fish and fisheries from the Western Mediterranean Sea

Small pelagic fish (SPF) species such as European sardine Sardina pilchardus, European anchovy Engraulis encrasicolus, round sardinella Sardinella aurita and European sprat Sprattus sprattus play important ecological roles in the Mediterranean Sea marine ecosystem. However, changes in SPF abundance and biomass have recently been observed in the basin. Therefore, uncovering the trophic importance of SPF to their predators is key to unravelling potential ecological causes and consequences of SPF population changes related to predator dynamics. Here, we reviewed 101 published studies reporting the presence of the SPF species named above in the diet of marine predators inhabiting the Mediterranean Sea. We found that the number of species preying on SPF was highest for teleost fish species, followed by elasmobranchs, seabirds, marine mammals, cephalopods and sea turtles. These predators were both commercial and non-commercial taxa, and vulnerability ranged from medium to very high. From a conservation point of view, most predator species were considered Least Concern by the IUCN, with few exceptions such as the Balearic shearwater Puffinus mauretanicus, a Critically Endangered species. Geographic information showed that the European sardine was more important in the diet of predators from the western Mediterranean basin, while European anchovy consumption was higher on the eastern side. Round sardinella was consumed in high amounts in the Tyrrhenian Sea, and European sprat was anecdotally consumed. The importance of SPF in the diet of Mediterranean predators may indicate bottom-up control of the marine ecosystem; however, limited temporal information precluded the evaluation of temporal changes, highlighting the need to develop new studies in this area.2,24