Trophic ecology of myctophids in the Patagonian shelf-break front

Myctophids are highly diverse and abundant mesopelagic fishes that play a pivotal role in trophic webs as consumers of planktonic organisms and as prey for top predators. Understanding their trophic interactions is essential for unravelling the dynamics and energy flow within pelagic ecosystems. This study assessed the trophic ecology of myctophids ( Electrona subaspera , Gymnoscopelus nicholsi , Protomyctophum spp.) near the Patagonian shelf-break front (PSBF) during austral spring. Stomach contents of 322 specimens were examined, and diet composition was expressed through numerical abundance (%N), frequency of occurrence (%FO) and relative importance (%RI). Multivariate analysis and multi-model inference were used to identify inter- and intraspecific differences in diet composition. In addition, dietary overlap among myctophids and prey selectivity were assessed. Results showed that myctophids fed almost exclusively on zooplanktonic crustaceans. Copepods were the most important prey for all myctophids, along with Themisto gaudichaudii juveniles (for E. subaspera ), adult euphausiids ( G. nichols i ) and ostracods ( Protomyctophum spp.). Interspecific differences in dietary composition were reflected in low to moderate trophic overlap. Dietary changes were observed with increasing myctophid total length, although these were not fully explained by prey size or type. There was selectivity for less abundant and lipid-rich prey such as T. gaudichaudii and adult euphausiids over the most available prey in the upper layer (i.e. Rhincalanidae and Calanidae). This study provides the first assessment of myctophid feeding ecology in the PSBF, improving our understanding of the pelagic ecosystem in this biologically and fisheries-relevant region of the southwestern Atlantic.