Biology subjects

Hirasaka, K.

Publications and source records attributed to Hirasaka, K..

5 recordsLinked to original sources

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

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↗

bioRxiv2023

The reciprocal regulation between mitochondrial-associated membranes and Notch signaling in skeletal muscle atrophy

Skeletal muscle atrophy and the inhibition of muscle regeneration are known to occur as a natural consequence of aging, yet the underlying mechanisms that lead to these processes in atrophic myofibers remain largely unclear. Our research has revealed that the maintenance of proper mitochondrial-associated endoplasmic reticulum membranes (MAM) is vital for preventing skeletal muscle atrophy in microgravity environments. We discovered that the deletion of the mitochondrial fusion protein Mitofusin2 (MFN2), which serves as a tether for MAM, in human iPS cells or the reduction of MAM in differentiated myotubes caused by microgravity interfered with myogenic differentiation process and an increased susceptibility to muscle atrophy, as well as the activation of the Notch signaling pathway. The atrophic phenotype of differentiated myotubes in microgravity and the regenerative capacity of Mfn2-deficient muscle stem cells in dystrophic mice were both ameliorated by treatment with the gamma-secretase inhibitor DAPT. Our findings demonstrate how the orchestration of mitochondrial morphology in differentiated myotubes and regenerating muscle stem cells plays a crucial role in regulating Notch signaling through the interaction of MAM. digestThis study investigated the link between Mfn2 and Notch signaling in skeletal muscle atrophy. We used a microgravity system to induce muscle atrophy and found that the loss of Mfn2 leads to decreased numbers of MAM and activation of Notch signaling and that treating MFN2-deficient human iPS cells with a gamma-secretase inhibitor DAPT improved their mitochondrial morphology and function. Additionally, Mfn2-deficient muscle stem cells in mice have a lower capacity to regenerate dystrophic muscles and DAPT treatment improves the regeneration of these cells. The study suggests that targeting the Notch signaling pathway with a gamma-secretase inhibitor could be a therapeutic option for skeletal muscle atrophy caused by defects in Mfn2.

developmental biology↗

bioRxiv2019

Identification of a fatty acid-sensitive interaction between mitochondrial uncoupling protein 3 and enoyl-CoA hydratase 1 in skeletal muscle

Skeletal muscle mitochondrial fatty acid (FA) overload in response to chronic overnutrition is a prominent pathophysiological mechanism in obesity-induced metabolic disease. Increased disposal of FAs is therefore an attractive strategy for intervening in obesity and related disorders. Skeletal muscle uncoupling protein 3 (UCP3) activity is associated with increased FA oxidation and antagonizes weight gain in mice on obesogenic diets, but the mechanisms involved are not clear. Here, we show that UCP3 forms a direct, FA-stimulated, mitochondrial matrix-localized complex with the auxiliary unsaturated FA-metabolizing enzyme, {Delta}3,5-{Delta}2,4dienoyl-CoA-isomerase (ECH1). Expression studies in C2C12 myoblasts that functionally augments state 4 (uncoupled) respiration and FA oxidation in skeletal myocytes.\n\nMechanistic studies indicate that ECH1:UCP3 complex formation is likely stimulated by FA import into the mitochondria to enhance uncoupled respiration and unsaturated FA oxidation in mouse skeletal myocytes. In order to characterize the contribution of ECH1-dependent FA metabolism in NST, we generated an ECH1 knockout mouse and found that these mice were severely cold intolerant, despite an up-regulation of UCP3 expression in SKM. These findings illuminate a novel mechanism that links unsaturated FA metabolism with mitochondrial uncoupling and non-shivering thermogenesis in SKM.

biochemistry↗