Biology subjects

Tsuchida, S.

Publications and source records attributed to Tsuchida, S..

5 recordsLinked to original sources

bioRxiv2026

Tractometry reproducibility and generalizability across scanners, scanner models, and acquisition protocols

Diffusion-weighted magnetic resonance imaging (dMRI)-based tractometry enables the quantification of white matter tissue properties in living humans while preserving anatomical specificity. Although tractometry is highly reproducible when the same scanner and acquisition protocol are used, its generalizability across scanners and protocols remains unclear. To address this gap, we performed a traveling-head experiment involving five subjects to evaluate tractometry across progressively different acquisition conditions, including multiple scanners, different scanner models, and two distinct protocols. Tractometry was performed for 20 major white matter tracts using diffusion tensor imaging metrics, neurite orientation dispersion and density imaging (NODDI) metrics, and a semi-quantitative ratio metric (T1w/b0). Generalizability across dataset pairs was quantified using the intraclass correlation coefficient (ICC). Tractometry showed consistently high ICCs when the scanner and protocol were identical; however, ICCs declined as differences in scanner model and acquisition protocol increased. Fractional anisotropy and orientation dispersion index retained relatively high ICCs across these comparisons, whereas other metrics showed marked declines when scanners or protocols differed. ComBat harmonization partially mitigated these declines, but ICCs did not reach the levels observed for datasets acquired using identical scanners and protocols. Finally, the minimum detectable change (MDC) for tractometry in datasets pooled across scanners and protocols varied by tract; for example, the optic radiation showed a lower MDC than the cingulum hippocampus. These findings highlight both the strengths and limitations of tractometry in multisite studies and highlight the importance of quantifying scanner- and protocol-dependent effects for specific metrics and tracts when interpreting measurements from heterogeneous datasets.

neuroscience↗

bioRxiv2026

Three-dimensional redistribution of pelagic fish aggregations associated with floating offshore wind farms

Floating offshore wind farms (F-OWFs) are rapidly expanding into offshore pelagic environments, yet their ecological consequences remain poorly resolved because quantitative, non-invasive monitoring is challenging at sea. Here, we integrated environmental DNA (eDNA) metabarcoding and scientific echosounding to assess fish community composition and three-dimensional aggregation structure around a commercial-scale F-OWF off the Goto Islands, Japan. We compared four stations adjacent to turbines with four offshore control stations under comparable environmental conditions across five sampling periods (April and August 2024; May, June, and August 2025) and three depth layers (5, 50, and 80-160 m). eDNA metabarcoding detected 126 fish species, and community structure based on the 30 most frequently detected taxa did not differ significantly between the F-OWF and control areas (Bray-Curtis PERMANOVA, p = 0.60). Species richness varied strongly with sampling period and water layer, with a significant water layer x period interaction, whereas overall richness did not differ between areas (Mann-Whitney U test, p = 0.18). In contrast, acoustic surveys revealed a marked difference in vertical structuring of fish aggregations: in the control area, NASC per mile increased with depth, while this depth-dependence disappeared near turbines. Moreover, the weighted mean normalized depth (WMND) indicated a shallower vertical center of aggregation in the F-OWF area (0.34) than in the control area (0.24), consistent with turbine-associated redistribution in the water column. Although voyage-level integrated NASC per mile did not differ significantly between areas (t-test, p = 0.83), mean values were higher near turbines. Together, these results indicate that F-OWFs can be associated with changes in the three-dimensional organization of fish aggregations without producing pronounced shifts in dominant taxonomic composition. Our study demonstrates the value of combining eDNA metabarcoding and acoustics for evaluating ecological effects of offshore renewable-energy infrastructures and provides a framework for standardized, long-term monitoring as F-OWF deployment accelerates globally.

ecology↗

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↗

bioRxiv2023

Environmental DNA Reveals the Geographic Distributions of Two Eel Species, Anguilla japonica and A. marmorata, in Western Kyushu, Japan

Anguillid eels migrate thousands of kilometres from their spawning grounds, dispersing across a vast geographic area to fresh and brackish water habitats, where they settle and grow. Japanese eels (Anguilla japonica) and giant mottled eels (A. marmorata) are both found in Japan, although their distributions differ. However, details of these differences are unknown. We hypothesised that distribution patterns of Japanese and giant mottled eels must be different between and within rivers along the northwest coast of Kyushu, Japan. Environmental DNA (eDNA) analysis was conducted at 87 sites in 23 rivers. Japanese eel eDNA was detected in 19 rivers (82.6%) and that of giant mottled eels was detected in 8 (34.8%). eDNA for Japanese eels was detected at 6 of 9 sites in the North (66.7%), 13 of 23 sites in Omura (56.5%) and 37 of 55 sites in the South (67.3%). In contrast, giant mottled eel eDNA was detected at 1 of 9 sites in the North (11.1%), no sites in Omura and 15 of 55 sites in the South (27.3%). There was no correlation between eDNA concentrations of the two species at 10 sites in the five rivers where eDNA of both species was detected, implying that their habitat preference differ. This partially reveals dispersal and settlement mechanisms of these eel species.

ecology↗