Biology subjects

Uchida, J.

Publications and source records attributed to Uchida, J..

3 recordsLinked to original sources

bioRxiv2025

Intraspecific differences in habitat depth in a deep-sea isopod, Bathynomus doederleini (Crustacea: Isopoda: Cirolanidae), off the west coast of Kyushu, Japan

The giant deep-sea isopod, Bathynomus doederleini, is a benthic scavenger distributed in the northwestern Pacific. Despite its ecological importance, little is known about its habitat use and intraspecific variation in body size in relation to depth. In this study, we examined the habitat depth, size structure, and distributional limits of B. doederleini off the western coast of Kyushu, Japan, using baited traps deployed at depths ranging from 151 to 821 m. A total of 1,152 individuals were collected, with the highest catch per unit effort (CPUE) observed between 300 and 500 m. CPUE declined sharply below 700 m, likely due to thermal constraints and interspecific competition. Body size distribution varied significantly with depth: minimum body size increased with depth, while maximum body size remained constant. Smaller individuals were more abundant in shallower, warmer waters, suggesting ontogenetic habitat segregation possibly driven by metabolic and competitive factors. No brooding individuals were captured, supporting previous findings that reproductive females avoid baited traps. These results suggest that B. doederleini forms a reproductively active population in the East China Sea, with ecological adaptations to thermal conditions and depth-related niche partitioning. This study highlights the importance of trap type and environmental gradients in understanding deep-sea species ecology.

ecology↗

bioRxiv2025

Floating offshore wind farms cause Japanese horse mackerel to congregate

Floating offshore wind farms (F-OWFs) are becoming key components of renewable energy production, yet their ecological impacts on marine ecosystems remain largely unexplored. Using environmental DNA (eDNA) analysis in the East China Sea, this study investigated the tendency for Japanese horse mackerel (Trachurus japonicus) to congregate beneath F-OWFs. Water samples were collected at stations near an F-OWF and control stations farther away at various depths and seasons. A total of 115 samples were analyzed, and eDNA of T. japonicus was detected in 83% of all samples. eDNA concentrations were significantly higher near an F-OWF (F-OWF stations) than at control stations. The highest recorded eDNA concentration reached 2,280 copies/L at an F-OWF station, whereas the maximum concentration at control stations was 783 copies/L. Seasonal variations were also observed, with lower concentrations in summer and higher concentrations from autumn to spring. Generalized linear model (GLM) analysis further revealed that wind turbines had a significant influence on eDNA concentration, whereas other environmental variables, such as water temperature and depth, were not significant. These findings suggest that F-OWFs may function as artificial reefs, providing habitat for commercially important fish and influencing fish distributions at both spatial and temporal scales. However, potential conflicts with fisheries due to spatial restrictions, displacement of fishery resources, and increased navigation costs necessitate further long-term ecological and socio-economic assessments. Integrating eDNA monitoring with traditional survey methods, such as acoustic surveys and ROV observations, is crucial for coexistence of adaptive offshore wind farm management and sustainable fisheries. Future research should also explore the long-term effects of F-OWFs on fish assemblages and biodiversity to support evidence-based decision-making for offshore energy development.

ecology↗

bioRxiv2021

Microplastic pollution of commercial fishes from coastal and offshore waters, Japan

Microplastics (MPs) pollution is a worldwide issue in the marine environment. There is growing concern of consuming MPs through fish, yet the current contamination status of fish collected from the deep sea surrounding Japan remains limited. We present baseline data on MPs in commercially important fishes from the coastal and offshore waters near Kyushu, Japan (East China Sea). We examined the MPs in the digestive tracts of two pelagic (n = 150 in total) and five demersal species (n = 235 in total). The fish were caught by pole and line, and bottom trawl at different geographical positions. The MPs in pelagic fish (39.1 %) were higher than demersal fish (10.3 %) and of larger sizes. The MPs correlated with habitat depth and type. There was species variation in the shape and polymer composition of MPs. These results increase our understanding of the heterogeneous uptake of MPs by fishes.

ecology↗