Trophic niche overlap between round sardinella ( Sardinella aurita) and sympatric pelagic fish species in the Western Mediterranean

Abstract

The northward expansion of round sardinella ( Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine ( Sardina pilchardus) and anchovy ( Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ ¹⁵N) and carbon (δ ¹³C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.

Abstract

The present study studies the trophic ecology of sardinella, anchovy, and sardine in the NW Mediterranean Sea, combining microscope visual analysis with DNA metabarcoding in gut contents as well as stable isotope analysis in muscle. Results with high taxonomic resolution determined an important degree of trophic niche overlap between the three species, which adapt their feeding to a wide range of available plankton, from the phytoplankton as well as the smallest copepods to larger krill or jelly organisms. Therefore, in the Mediterranean pelagic fish community, the diet plasticity of the recently incorporated (and expanding) sardinella might increase the inter‐specific competition if the food availability changes in the future.