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ABSTRACT Macrobenthic communities in a lake are affected by the type of bottom cover such as macrophytes or algae. In the southern basin of Lake Biwa, mats of the benthic cyanobacteria (BC) Microseira wollei widely cover the lake bottom and are interspersed with submerged macrophytes (SMs). Because different macrobenthos species appear to occur at those bottoms, we investigated the composition of the communities. Furthermore, as M. wollei is supposed to be inedible to consumer organisms owing to its hard sheath and toxins, the food possibility of the cyanobacteria and macrophytes for macrobenthos was analyzed. In this study, macrobenthos were collected, identified molecularly, counted in the BC and SM zones, and analyzed for carbon and nitrogen stable‐isotopic compositions. In the BC zone, asellids and amphipods dominated the macrobenthic community, while chironomids dominated the SM zone. The stable‐isotope analysis revealed that M. wollei was a minor food source for macrobenthos and other higher‐level consumers, with some macrophytes, particulate organic matter and bottom sediment potentially being a major source. The dominance of crustacean macrobenthos in M. wollei mats suggested that they provided a refuge from predation for crustaceans, whereas SMs were not sufficiently abundant to achieve this. Although different macrobenthic communities in the BC and SM zones were likely supported by common food sources, with the exeption of M. wollei, the present study was conducted over a short period and lacked advanced methods for gut content analysis. Therefore, further monitoring and food web analysis are required.

Upogebia major (De Haan, 1841) is known for forming huge burrows in sandy, intertidal areas that can extend to depths of over 2 m. Despite its widespread distribution in East Asia and Russia, the genetic relatedness of its regional populations remains uncertain, likely owing to difficulties in specimen collection. Therefore, to appraise the phylogeographic patterns, genetic diversity, and morphological variety of U. major, the mitochondrial DNA of specimens collected from Japan, Korea and China were subjected to molecular phylogenetic analyses of COI genes, alongside morphological assessment. As a result, we discovered four principal groups; of these, Group 1 consisted predominantly of Japanese specimens, while Groups 3 and 4 were interpreted as having originated from the continent. Group 2 exhibited genetic segregation from both continental and Japanese descent. Group 1 mostly comprising Japanese specimens implies that the planktonic larvae of U. major were disseminated north and south by ocean currents encompassing the Japanese archipelago. In contrast, individuals probably originating from the continent were discovered in Lake Notoro, Hokkaido and Matsukawa-ura, Fukushima in northeastern Japan, indicating possible introduction from the continent through ocean currents or unintentional introduction with other organisms imported. Additionally, one of the specimens collected from Matsukawa-ura exhibited significant genetic and morphological differences from other specimens, suggesting the possibility of being a subspecies. The outcomes of this study not only offer valuable insights into the origins of distribution of U. major but also introduce a novel challenge of assessing the coexistence of two routes: natural and anthropogenic dispersion.

Abstract In summer, the survival zones of cold‐water species are predicted to narrow by both increasing water temperatures from the surface and by expanding hypoxic zones from the lake bottom. To examine how the abundance of cold‐water fishes changes along environmental gradients, we assessed the vertical environmental DNA (eDNA) distributions of three salmonid species which may have different water temperature tolerances during both stratification and turnover periods using quantitative PCR (qPCR). In addition, we examined on the vertical distribution of diverse fish fauna using an eDNA metabarcoding assay. The results suggested that the kokanee salmon (Oncorhynchus nerka) eDNA were abundant in deep, cold waters. On the other hand, rainbow trout (O. mykiss) eDNA were distributed uniformly throughout the water column, suggesting that they may have high water‐temperature tolerance compared with kokanee salmon. The eDNA concentrations of masu salmon (O. masou) were below the detection limit (i.e.,

Managing legacy nitrogen (N) that has accumulated over decades of intensive agriculture is necessary to balance agricultural production and environmental conservation. Using legacy N as a resource can reduce extant legacy N. The uplands of Japan's Lake Inba watershed are dominated by agroecosystems, and spring waters in the lowlands contain high NO3-N concentrations. We focused on an unfertilized, commercial lotus (Nelumbo nucifera) farm where paddy fields are irrigated with spring waters. We hypothesized that the lotus field could reduce the export of legacy N and provide habitat for fish (co-benefit). Dating of spring waters using sulfur hexafluoride revealed that the residence time of water at the study site was 12.5 years and suggested that the spring waters contained legacy N. We found large reductions of NO3-N and total nitrogen (TN) concentrations in water that passed through the lotus fields. A meta-analysis revealed that the reductions of NO3-N concentrations were highest in unfertilized lotus fields, and reductions of TN concentrations were higher in unfertilized paddy and lotus fields than in fertilized fields. The N removal by harvesting lotus roots 38.7 kg N/ha/year was smaller than the literature-based rate of N removal by denitrification. We used environmental DNA metabarcoding to identify the fish fauna in the lotus fields and an adjacent stream. The native fish richness was a little lower in the lotus fields than in the stream, but the presence of two endangered fish species in the lotus field suggested a moderate biodiversity conservation function. Our case study could be a good example of a nature-based solution to harness ecosystem functions to reduce legacy N.

Evaluating the spatial genetic structure of rare species is important because it could provide information on the degree of habitat fragmentation and effective population size that are necessary for conservation planning. We examined the genetic structure of the grassland butterfly Plebejus argyrognomon that has severely declined in recent decades using single nucleotide polymorphisms obtained by the MIG-seq method. The study region was in the southern Ina Basin located in central Japan, where P. argyrognomon inhabits grasslands in agricultural field margin as well as in riverbank. We found a positive association between genetic and geographic distances, but the pattern was nonlinear, with little change in genetic distance above 12 km. The genetic differentiation was considerable, as demonstrated by FST and Structure. Moreover, genetic diversity was positively associated with habitat connectivity index, suggesting severe genetic drift in isolated populations. Comparing two habitat types, the genetic structure tended to be similar among agricultural field margin populations while dissimilar among riverbank populations, suggesting frequent gene flow in the former. Coupled with the presence of many habitat patches in agricultural field margin, we consider that agricultural field margin populations in the northern part of the study sites appear valuable to ensure long-term persistence of the regional P. argyrognomon population. [ABSTRACT FROM AUTHOR]