Trophic Connectivity of Pelagic Ecosystems in the Western Pacific Ocean and Its Marginal Seas Inferred From Stable Isotope Analysis

We used carbon and nitrogen stable isotope ratios to quantitatively assess predator–prey relationships among predatory fishes and their prey in the pelagic and mesopelagic layers of the East China Sea, the Sea of Japan, and the Pacific Ocean around southern Japan. Predatory fishes and their potential prey were collected from each region to evaluate spatial and species‐level differences in trophic structure. Isotopic niche widths were evaluated for prey taxa by region using standard ellipse areas corrected for small sample sizes. Overall, niche widths of predatory fishes in the Sea of Japan were larger than those in the Pacific Ocean. Niche overlap between the Pacific Ocean and the other regions was limited. Collectively, niche widths and niche‐overlap results were consistent with greater isotopic similarity between the East China Sea and the Sea of Japan, whereas the trophic structure of the Pacific Ocean was more distinct. Bayesian mixing model analysis suggested that Evermann's lanternfish ( Symbolophorus evermanni ) and prickly lanternfish ( Myctophum asperum ) were important inferred prey sources for several predators in the Pacific Ocean, whereas pearlside ( Maurolicus japonicus ) contributed substantially to several predator groups in the East China Sea. These findings suggest that micronekton may represent an important energy pathway supporting predatory fish communities in the Pacific Ocean and the East China Sea.