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 (δ¹³C) and nitrogen (δ¹⁵N) values (± SD) between the north (δ¹³C: −19.9 ± 0.3 ‰; δ¹⁵N: 6.2 ± 0.9 ‰) and south (δ¹³C: −20.5 ± 0.7 ‰; δ¹⁵N: 8.5 ± 2.3 ‰) regions, while G. bolini (south only) had average values of δ¹³C: −20.4 ± 0.6 ‰, δ¹⁵N: 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 δ¹³C and δ¹⁵N 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.