Abstract The study of fish movement patterns in freshwater ecosystems remains a major focus of contemporary research. Small freshwater fish are known to migrate between tributaries and mainstems at different stages of their life history, helping to avoid local extinctions and maintain genetic diversity. However, fitting small fish species with telemetry equipment is difficult, making it challenging to track their detailed migration history via conventional methods. We evaluated the suitability of otolith isotope analysis for verifying the migration histories of small fish species inhabiting small tributaries. In this study, we compared the 87 Sr/ 86 Sr values in stream water and the otoliths of two fish species ( Nipponocypris temminckii and Rhinogobius flumineus ) inhabiting small streams. The 87 Sr/ 86 Sr ratios in the stream waters within the study area displayed considerable variation among tributaries. Our findings indicate that only N. temminckii has high dispersal ability, showing movement between tributaries or between tributaries and the mainstem in some locations. In contrast, such movement was not generally observed for R. flumineus . These results show the potential of 87 Sr/ 86 Sr as a tool for estimating the migration patterns of small fishes that inhabit small tributaries.

Abstract Deep‐sea hydrothermal vents are biological hotspots driven by microbial chemosynthetic primary production and characterized by a high proportion of endemic, specially adapted species. Vent communities can be unstable depending on the geological setting, as the underlying geofluid supply may change in location and chemical composition over a decadal timescale. Although the Izu‐Ogasawara Arc in Japan is home to many vent fields within an Ecologically or Biologically Significant Marine Area (EBSA), no observations of decadal changes have been conducted. On Mokuyo Seamount, venting was first confirmed by several submersible dives between 1990 and 1993, but only fragmentary information has been published on its biodiversity. Here, we revisited Mokuyo on two dives between 2021 and 2024, three decades after its discovery. We found changes in venting activities, with the fluid supply on the northern caldera wall almost completely waned, while the northeastern face of the central cone has become increasingly active. The northwestern ridge of the central cone was covered in a dense white plume, under which xenophyophores (giant protists) thrive. The first comprehensive faunal sampling at Mokuyo greatly updated the faunal list from three to 18 species. Our results suggest vent communities on the Izu‐Ogasawara Arc shift on a decadal scale, providing key baseline data for future conservation planning of the EBSA.

Abstract Dissolved organic matter and nutrients released from leaf litter are important cross‐ecosystem resources supporting freshwater food webs. Dissolved organic matter supports heterotrophic organisms in freshwater communities. However, the role of nutrients released from leaf litter in the autochthonous production in aquatic ecosystems is not well understood. Therefore, we investigated how dissolved nutrients released from leaf litter affect algal growth, biomass production, and cellular elemental ratios. Specifically, we experimentally examined the response of green algae to nitrogen (N) and phosphorus (P) released from leaf litter of 11 temperate tree species and the degree of deficiency of nutrient elements other than N and P relative to algal demand in these litter leachates by supplementing these elements. We found that algal growth did not significantly increase with dissolved N or P in the leaf leachates. In contrast, algal biomass production increased with dissolved N concentration, regardless of amendment. Algal growth and production limitation by deficiency of elements other than N and P was found only in the leachate of Japanese hemlock, indicating that the concentrations or release efficiencies of these elements in this leaf litter were lower than those of N and P relative to algal requirements. More importantly, leaf litter leachates from different tree species altered algal cell quotas and C:N:P ratios, which would affect secondary production. These results suggest that variations in leaf litter leachate stoichiometry caused by vegetation change would affect the abundance and chemical composition of phytoplankton, and thus the trophic transfer efficiency between phytoplankton and herbivorous zooplankton.

Abstract Fine root morphological traits regulate the belowground resource acquisition strategies of trees. Therefore, investigating genotypic variations isolated from environmental variations within tree species helps in understanding how genotypic backgrounds affect intragenerational tree acclimation to the growing environment. Thus, this study aimed to clarify the effects of genotypic variations on the fine root morphology of three types of Japanese cedar ( Cryptomeria japonica ), which were derived from different provenances but were grown in a common garden. In the three geographically different provenances of C. japonica stands (Yanase, Yoshino, and Yaku), fine root morphological traits, such as root length and diameter and specific root length (SRL), were measured for each root up to the 4th branching order. Yaku cedar exhibited root traits distinct from the other provenances, such as growing longer and thinner roots in 1st root order to enhance root surface area. In addition, the SRL patterns with root orders and higher root tissue density suggested a resource conservation strategy. Yanase cedar demonstrated a significantly higher root branching ratio and specific root tips than the other provenances, indicating a strategy for investing resources in absorptive roots. Although Yoshino cedar had traits similar to those of Yanase cedar or intermediate between Yanase and Yaku cedars, high aboveground production may be achieved through nutrient acquisition with root exudates instead of absorptive root growth. Genotypic variations appeared in fine root morphological traits of C. japonica trees, even when grown in the same environments, implying distinct resource acquisition strategies characterized by each provenance.

Abstract For 40 years, Model of Acidification of Groundwater In Catchments (MAGIC) has been used to simulate the acidification of soils and waters due to acid deposition. The original model (MAGIC v8) has now been updated and re‐implemented in the C++ Mobius platform and is available as open source. MAGIC‐Forest includes new modules describing hydrology, forest growth, and soil carbon. The Mobius platform facilitates automatic optimization of calibrated parameters and multipoint calibrations using Monte‐Carlo routines. The usefulness of MAGIC is demonstrated here by application to the 50‐year data series for deposition and runoff at Birkenes, a small, calibrated catchment in southern Norway. Acid deposition has declined dramatically at Birkenes since the peak in the 1970s. Sulfate is 90% lower. Stream water has recovered strongly. Decreased concentrations of sulfate have led to increased acid‐neutralizing capacity, pH, and reduced concentrations of toxic aluminum. These changes are well‐simulated by MAGIC. The sulfate control on organic carbon solubility added as part of MAGIC‐Forest improves the simulations. The MAGIC‐Forest modeling tool is now available for applications to scenarios of land‐use and climate change.

Abstract Hyperaccumulator plants are a botanical curiosity that have allowed the development of agromining of metals, with a special focus on nickel. In nickel agromining, this element is recovered from ashed hyperaccumulators cultivated on metal‐rich soils. In order to explore bio‐based approaches for the decomposition of hyperaccumulator biomass and nickel recovery that do not include burning, we performed a vermicomposting experiment using the earthworm species Eisenia andrei and the biomass of Bornmuellera emarginata (which contained almost 1% of nickel). We conducted our experiment for 12 weeks and assessed the decomposition process of the hyperaccumulator biomass, changes in earthworm number and biomass, and changes in nickel concentration and mobility. Despite the initial mortality and an increase of Ni concentration in earthworm tissues, E. andrei was able to decompose B. emarginata biomass. This process also showed a massive colonization of the biomass by a fungus during the first weeks of the assay. Our results indicate that the vermicomposted hyperaccumulator biomass had a higher nickel concentration than the starting material but the diethylenetriaminepentaacetic acid‐extractable nickel decreased. At the same time, due to earthworm activity, the nickel was redistributed and diluted in the vermicompost bedding, reducing the interest of this approach for agromining, but opening the perspective of using the vermicomposted hyperaccumulator biomass as an organic amendment in nickel‐deficient crops.

Abstract Mountain streamwater chemistry is an effective indicator of forest condition. In 2022, we conducted a nationwide investigation of mountain streamwater chemistry in Japan, leveraging citizen‐participatory sampling. This approach involved 629 individuals with regular exposure to mountain and natural environments. Although our primary aim was to sample at locations from a 2003 study, we also welcomed samples from new sites. In total, 1414 streamwater samples were collected one time from each forested watershed at the baseflow condition. Our study focused on stream nitrate (NO3−) concentration as a key indicator of anthropogenic nitrogen (N) loading impacts on forests. We compared NO3− concentrations in 2022 with those from 2003 at identical sampling points. After excluding 179 points with evident human‐created features upstream, the mean NO3− concentration in 2022 was 0.328 mg N L−1 (n = 1236). Comparing data from 1088 points sampled in both years, the mean value in 2022 (0.324 mg N L−1) was significantly lower than that in 2003 (0.359 mg N L−1, p < 0.05). Notably, 88.5% of sampling points showed differences within ±0.25 mg N L−1. The spatial distribution pattern of mountain stream NO3− concentrations in 2022 did not consistently align with large cities, industrial areas, or N deposition sources. This unique approach marked the first nationwide participatory survey for collecting mountain streamwater in Japan. Our success in ensuring sample quality through accessible explanations, manuals, and videos demonstrates the potential of citizen science. However, the quantitative evaluation of scientific accuracy remains a forthcoming challenge.

Abstract Few studies have evaluated the structure and dynamics of forests in Madagascar with high levels of endemism. Ankarafantsika National Park holds the largest of the remaining primary dry forests in northwestern Madagascar, where most of the forests have been lost or degraded by fire and other human activities. In this primary forest, we established a 15‐ha forest dynamics monitoring plot and mapped and identified all woody stems with a diameter at breast height (DBH) ≥5 cm. The forest stand was characterized by small‐sized individuals (75% of stems with DBH <10 cm, with 99% of trees with height <15 m), encompassing 35,758 tree and 513 liana individuals belonging to 160 species in 53 families (including 20 species of lianas accounting for 1.4% of the stems). Most species‐rich families were Rubiaceae, Fabaceae, Lamiaceae, and Malvaceae, which together encompassed 43 tree species and 23% of all tree individuals. The plot was located on a hill consisting of white sand at elevations from 150 to 200 m, with a gentle slope down from southwest to northeast. Over this elevation gradient, stem density and species diversity increased with elevation, while tree height and diameter decreased. The most abundant two species, Drypetes perrieri (Putranjivaceae) and Noronhia alleizettei (Oleaceae) are evergreen, suggesting the importance of a nutrient conservation strategy. These results provide the foundational knowledge necessary for the conservation and restoration of natural semi‐deciduous dry forests that used to cover large areas in northwestern Madagascar until recently.

Abstract The two‐spotted spider mite, Tetranychus urticae Koch (Acarina, Tetranychidae), is a notorious agricultural pest known for its high dispersal ability. Understanding the dispersal patterns of T. urticae is crucial for studying its population dynamics and assessing the risk of gene dispersal related to acaricide resistance. We investigated the impact of surrounding landscapes on T. urticae occurrence and detected gene flow between nearby apple orchards. Land use data within 0.2–2 km radius buffers of the orchards were extracted and summarized using principal component analysis. The effects of landscape composition on the occurrence of T. urticae in apple orchards were analyzed using a hierarchical Bayesian model that considers spatial autocorrelation. In addition, we conducted a population genetic analysis on samples collected from five orchards. The results indicate that the best model was one at a 200‐m scale, revealing a positive correlation between forest area ratio and T. urticae occurrence. The population genetic analysis demonstrated distinct genetic structures within T. urticae populations across different orchards. However, we estimated gene flow among some orchards that were geographically close. These findings suggest that T. urticae may migrate from surrounding landscapes, particularly forests, and nearby orchards to apple orchards. These findings have substantial implications for developing control units based on the gene flow range of the two‐spotted spider mite, as well as for assessing the risk of infestation in each orchard.