Presence of the Non‐Indigenous Copepod <scp> <i>Pseudodiaptomus marinus</i> </scp> Sato, 1913 in the Stomach Content of <scp> <i>Sardina pilchardus</i> </scp> (Walbaum, 1792)

ABSTRACT The increasing presence of non‐indigenous species (NIS) in marine ecosystems, particularly copepods, poses significant ecological questions concerning their integration into local food webs. This study presents the first record of the NIS Pseudodiaptomus marinus in the diet of Sardina pilchardus (European sardine) in the Mediterranean Sea, based on stomach content analysis of individuals collected from Thermaikos Gulf. Out of the 174 sardines examined, P. marinus was found in five of the stomachs, all during spring. All fish individuals that were found to have consumed P. marinus were males, at a 2–3 sexual maturity stage and their stomachs were full according to the Lebedev index. The findings suggest that this NIS copepod may already be contributing to the diet of native pelagic fish, highlighting potential ecological implications including trophic integration and shifts in prey dynamics. The selective absence of P. marinus in anchovy ( Engraulis encrasicolus ) diets, despite overlapping ecological niches, raises further questions about prey selection mechanisms and diel feeding behavior. These findings underscore the importance of monitoring NIS within zooplankton communities to assess their long‐term impact on food web dynamics and fisheries in the Mediterranean Sea.