Feeding habits of six species of euphausiids (Decapoda: Euphausiacea) in the northwestern Pacific Ocean determined by carbon and nitrogen stable isotope ratios

• Published in: Journal of crustacean biology Vol. 37; no. 1; pp. 29 - 36
• Main Authors: Sogawa, Sayaka, Sugisaki, Hiroya, Tadokoro, Kazuaki, Ono, Tsuneo, Sato, Erika, Shimode, Shinji, Kikuchi, Tomohiko
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01-01-2017
• Subjects: Ecology; Oyashio; C; δ; trophic level; food web; transition area; Kuroshio; krill; N
• ISSN: 0278-0372; 1937-240X
• DOI: 10.1093/jcbiol/ruw014

The nitrogen (δ¹⁵N) and carbon stable isotope (δ¹³C) values of six species of euphausiids predominant in the northwestern (NW) Pacific Ocean were investigated to elucidate speciesspecific feeding habits and seasonal and regional differences. The order of annual mean δ¹⁵N values was: Tessarabrachion oculatum Hansen, 1911 (11.2 ± 0.8‰) > Thysanoessa longipes Brandt, 1851 (10.4 ± 0.4‰) > Thysanoessa inspinata Nemoto, 1963 (9.3 ± 0.8‰) > Nematoscelis difficilis Hansen, 1911 (8.2 ± 1.4‰) > Euphausia pacifica Hansen, 1911 (7.7 ± 0.5‰) > Euphausia gibboides Ortmann, 1893 (6.9 ± 0.9‰). The trophic levels of four species based on δ¹⁵N values were estimated as 3.6, 3.2, 2.9, and 2.5 for T. oculatum, T. longipes, T. inspinata, and E. pacifica, respectively, in the Oyashio region in June 2011. The seasonal differences in δ¹⁵N values of these species were relatively small, which suggests euphausiids play the same role in the food web throughout the year. Carapace lengths were negatively correlated with δ¹⁵N values of five species except T. longipes. Regional differences in stable isotope ratios that might reflect regional differences in the primary producer signature were observed: higher δ¹³C values and lower δ¹⁵N values in the Oyashio–Kuroshio mixed water region compared to those in the Oyashio region. The biplot of δ¹³C and δ¹⁵N annual mean values with zooplankton in the NW Pacific shows that euphausiids have a wide range of δ¹⁵N values, suggesting they play diverse roles in the pelagic food web in the region.