Biology subjects

Anzai, S.

Publications and source records attributed to Anzai, S..

3 recordsLinked to original sources

bioRxiv2026

Size-invariant aerobic scope across ontogeny in a giant deep-sea scavenger

Aerobic scope is the aerobic metabolism left after maintenance costs are met, and it sets a simple limit on how much oxygen-dependent activity an animal can support. In many aquatic animals, this margin changes with body size because resting and active metabolic rates do not always scale in the same way. Large deep-sea scavengers are interesting in this respect because they live where food is sparse and unpredictable, but they must still move when carrion or food cues appear. We measured resting metabolic rate (RMR) and post-exercise peak oxygen consumption, here referred to as active metabolic rate (AMR), in the giant isopod Bathynomus doederleini across a body-mass range of 1.7-48.4 g using intermittent-flow respirometry at 10 {degrees}C. RMR and AMR both increased with body mass and had similar scaling exponents. As a result, factorial aerobic scope (FAS = AMR/RMR) did not change with body mass (median FAS = 2.83). A residual analysis also showed that mass-corrected RMR was not significantly related to mass-corrected AMR. Thus, individuals with relatively high maintenance metabolism did not necessarily have higher post-exercise aerobic capacity. These results show that exercise-induced aerobic scope was maintained across ontogeny in this deep-sea scavenger. They also show that body size and individual metabolic phenotype provide different information: body size explained the shared increase in RMR and AMR, whereas residual variation did not show a strong link between the two traits.

physiology↗

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↗