Trophic position and partitioning differences between euphausiid species in the Southern California Current and eastern tropical North Pacific using stable isotope ratios (δ13C and δ15N), elemental composition, and lipid contents

Sympatric euphausiid species from the eastern tropical North Pacific (ETNP) and the California Current (CC) were tested for stable isotopes, elemental composition, and lipid content to evaluate geographic patterns and species-level trophic niche partitioning. Euphausia diomedeae and Thysanoessa spinifera showed higher δ15N in their respective regions. Trophic Position (TP) was higher in tropical vs. CC species; a significant difference in TP was found among the species. T. spinifera showed markedly higher values in isotopic signal, elemental composition, and total lipid content. Individual carbon was lower for tropical species, mainly because of their smaller sizes and lower lipid content. The higher TP in tropical species probably derives from their more complex food web. In each area, bigger species have a higher TP. Considering the formerly published isotopic baseline for the CC and the ETNP, the differences between the species from the two areas are, probably, also related to the marked differences in latitude (~ 11–12° N) and temperature (~ 12° C) between them, as well as to the expected differences in their trophic conditions.