Trophic ecology analysis of two lanternfish species (Gymnoscopelus bolini and Lepidophanes guentheri) suggests spatial niche segregation in the southwestern Atlantic Ocean

Myctophids play a vital role in pelagic food webs by connecting basal trophic levels to higher-order consumers. Despite their ecological importance and high abundance, the feeding habits of these fishes have not yet been fully investigated in the Southwest Subtropical Atlantic. We examined spatial variations in the trophic ecology of two lanternfish (Myctophidae: Myctophiformes) species ( Gymnoscopelus bolini and Lepidophanes guentheri ). The analyses were based on two different regions of the southwest subtropical Atlantic influenced by distinct oceanographic regimes: (a) the north (20–28°S) and (b) south (28–34°S). Stomach content analysis (SCA) revealed that G. bolini preyed mainly on Euphausia spp. and Copepoda (%FO: 18.2), and L. guentheri preyed mainly on Euphausia spp. (%FO: 10.3) and Chaetognatha (%FO: 3.4). Stable isotope analysis (SIA) revealed that L. guentheri had different mean carbon (δ 13 C) and nitrogen (δ 15 N) values (± SD) between the north (δ 13 C: −19.9 ± 0.3 ‰; δ 15 N: 6.2 ± 0.9 ‰) and south (δ 13 C: −20.5 ± 0.7 ‰; δ 15 N: 8.5 ± 2.3 ‰) regions, while G. bolini (south only) had average values of δ 13 C: −20.4 ± 0.6 ‰, δ 15 N: 9.6 ± 2.1 ‰. In the southern region, there was similarity between the diets of G. bolini and L. guentheri , and the isotopic niche overlap was also considerable (up to 92.9 %). When comparing the northern and southern regions, there were dietary differences for L. guentheri , as well as significant differences in δ 13 C and δ 15 N values ( p = 0.002). G. bolini and L. guentheri exhibited a generalist zooplanktivorous feeding behaviour. In addition, region seems to be a determining factor in the trophic ecology of Myctophidae. We hypothesized that the region influence is mainly due to the distinct oceanographic processes that affect primary productivity and the base of the trophic chain. • Diet composition and trophic ecology of two lanternfishes were studied. • The species exhibited a generalist zooplanktivorous feeding behaviour. • Key prey sources were euphausiids and copepods. • The diet likely undergoes ontogenetic variations. • We hypothesize that oceanographic processes in distinct areas are a determining factor in the ecology of Myctophidae.