Functional Assessment of Trophic Restructuring and Isotopic Niche Shifts in Macrobenthic Food Web Driven by Undaria pinnatifida Transplantation

Kelp transplantation is a nature-based strategy aimed at restoring coastal habitat integrity and marine biodiversity. However, its functional consequences for trophic integration within benthic food webs remain poorly understood. Using δ13C and δ15N stable isotope analyses, we evaluated how Undaria pinnatifida transplantation alters consumer trophic structures and isotopic niche characteristics in Oeyeondo, South Korea. While basal source remained isotopically uniform across sites, the introduction of U. pinnatifida triggered significant isotopic shifts in consumers, reflecting a reorganization of carbon assimilation pathways. At the transplanted site, herbivores exhibited significantly enriched δ13C values (−14.7 ± 2.0‰ to −13.2 ± 0.3‰) compared to the control site (−19.3 ± 1.2‰), indicating direct assimilation of kelp-derived carbon. Conversely, grazers showed depleted δ13C values (−20.6 ± 0.6‰) reflecting a shift toward alternative benthic resources. Isotopic niche metrics revealed a broader community-level niche width at the transplanted site, driven by increased resource diversity and niche partitioning. These findings demonstrate that kelp transplantation effectively restructures benthic food web dynamics by providing new energy pathways, offering a robust functional framework for evaluating marine forest restoration success.