Gender Differences in Foraging Behavior of the Euphausiid Euphausia pacifica in the East Sea (Japan Sea) in Spring

Abstract

Although it is known that there are gender differences in the energetic requirements for the reproductive strategies of euphausiids, sufficient information about differences in the feeding ecology is still lacking. In this study, we investigated the resource utilization of Euphausia pacifica within the epipelagic zone (0–200 m depth) in the East Sea (Japan Sea) during spring bloom, using stable isotope analysis. The δ13C and δ15N values of pico- to micro-particulate organic matters (POMs) from the surface to 200-m depth layers were significantly different. The δ13C and δ15N values of E. pacifica adults showed significant differences between sexes. Stable isotope analysis showed that E. pacifica females fed mainly on the surface layer POM, whereas the males fed primarily in the deeper layers, since the contributions of POMs in the 100-m and 200-m depth layers to their diets were relatively high. We suggest that high primary productivity in the surface layer in spring and the sinking particles derived from it may provide sufficient energy for the reproduction of E. pacifica females and male development, respectively.