[A-OS15] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS15-01] Quantifying the Front Effect: How Oceanic Fronts Shape Fish Community Distribution around Japan

★Invited Papers

*Yuan LIN^1,2, Zeshu YU¹, Sk Istiaque AHMED^1,2, Xueding WANG^1,2, Tomihiko HIGUCHI¹, Itsuka YABE³, Sachihiko ITO¹, Eisuke TSUTSUMI⁴, Hiroaki SAITO¹, Kosei KOMATSU¹, Atsushi TSUDA¹, Yusuke KAWAGUCHI¹, Eitarou OKA¹, Kyoko OKINO¹, Hajime OBATA¹, Yuki MINEGISHI¹, Hideki FUKUDA¹, Marty Kwok-Shing WONG¹, Jun INOUE¹, Susumu HYODO¹, Shin-Ichi ITO¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan, 3.Tokyo University of Marine Science and Technology,, 4.Faculty of Fisheries, Kagoshima University, Japan)

Keywords:Oceanic Fronts, Fish Community Structure, Environmental DNA, Seas around Japan

Oceanic fronts are regions in the ocean where environmental variables such as temperature, salinity, and nutrients exhibit sharp spatial changes. Fronts are often considered important ecological boundaries that influence the distribution patterns of marine organisms through physical and biological processes. Strong turbulence and upwelling associated with fronts can transport deep nutrients to the surface, enhancing phytoplankton productivity and thereby affecting the entire food web. On the other hand, as regions with distinct environmental gradients, fronts may serve as ecological boundaries for different fish communities. Additionally, certain fish species may tend to aggregate near fronts to take advantage of higher primary productivity and abundant prey resources. While previous studies have explored the impacts of fronts on fisheries resources, their fine-scale effects on fish community structure remain unclear, especially in the complex marine environment around Japan.
In this study, we analyzed environmental DNA (eDNA) data from 17 research cruises conducted between 2018 and 2023 to investigate how oceanic fronts influence fish distributions in Japanese waters. Front regions were identified based on temperature gradients (25–20°C, 20–15°C, and 15–10°C), and temperature-species richness curves were constructed for both frontal and non-frontal regions to quantify the "front effect." Generalized Additive Models (GAMs) were used to assess the influence of key environmental factors—including front strength, offshore distance—on fish community structure.
Our results indicate that fish species richness is generally higher in frontal regions than in non-frontal regions, with the strongest front effect observed in areas with temperature gradients between 20–15°C. Furthermore, fish community composition differed significantly between frontal and non-frontal areas, suggesting that oceanic fronts function as ecological boundaries that modulate fish community structure.
These findings provide new insights into the role of oceanic fronts in shaping marine biodiversity and highlight their importance for ecosystem-based fisheries management. Further analysis incorporating salinity, chlorophyll, and other environmental gradients will enhance our understanding of the mechanisms driving fish community dynamics in frontal regions.