Interdisciplinary approaches at early invasion stages maximise the evidence on human-induced and climate-driven fish dispersal

Species range shifts have manifold consequences on the biota and functioning of recipient ecosystems. A thorough assessment at early dispersal stages may effectively contribute to foreseeing the outcomes implied. Here we capitalised on a combination of interdisciplinary tools to investigate the taxonomy, native ranges, invasion pathways, and impacts of four fish samples exotic to the Mediterranean. These are Zenopsis conchifer and Ephippion guttifer, two neonative species from the Atlantic, and Epinephelus striatus and “Siganus clade C”, two new non-indigenous species (NIS) that are respectively critically endangered in the central-western Atlantic and potentially undescribed and native to the eastern Indo-Pacific. Faunal, molecular, and parasitological analyses suggested that neonatives still had an extra-Mediterranean origin, whereas NIS arrived through shipping. Dietary analyses showed that E. guttifer and E. striatus fed on multiple trophic levels and survived in the area of introduction scavenging on fisheries discards. This study contributes to solving taxonomic issues, shows how stomach content metabarcoding and parasite biotagging can aid monitoring species dispersal, and highlights the potential role of bycatch dumping in NIS spread. Finally, it emphasises how interdisciplinary approaches maximise evidence and proposes a workflow that may be applied to similar circumstances worldwide.