Biology subjects

Negishi, J.

Publications and source records attributed to Negishi, J..

5 recordsLinked to original sources

bioRxiv2025

Contribution of the lateral extension of the hyporheic zone in gravel bars in shaping river invertebrate diversity

Gravel bars (GBs) and hyporheic zone (HZ) are two major natural geomorphic features in gravel-bed rivers, having multiple functions ranging from habitat provisioning to nutrient cycling. This study examines whether the lateral extension of HZ in GBs contributes to the total diversity of river aquatic invertebrates. The hyporheic invertebrate community composition was entirely dissimilar from the benthic habitat, with stable GB hyporheic location exhibiting a more distinct community composition compared to wetted channel and active GB across all seasons. The local contribution to beta diversity (LCBD) also showed that stable GB has significantly higher uniqueness across all seasons, indicating a more unique invertebrate community. Species contribution to beta diversity (SCBD) indicates that this uniqueness was mainly driven by hyporheic dwelling species amphipod, Pseudocrangonyx yezonis, and Isopod species. Distance from wetted channel and dissolved oxygen were the factors influencing hyporheic invertebrates distribution. These findings show that the maintenance and restoration of gravel bars are crucial to enhancing and maintaining the overall invertebrate diversity in the river ecosystem.

zoology↗

bioRxiv2023

An urbanized phantom tributary subsidizes river-riparian communities of mainstem gravel-bed river

Urbanization transforms natural river channels, and some rivers become invisible over time. How and whether the subsurface domains of the original waterways and aquifers connecting them (a phantom of historical landscape) are functional is not known. This study examined the effects of tributary groundwater (GW) inflow on the response of river-riparian organisms in an alluvial mainstem river in northern Japan, where the tributary disappeared over the course of urban landscape transformation. A 2.8-km long lowland segment of the mainstem gravel-bed river was examined for water properties and the river-riparian food web. In addition, watershed-wide water sampling was conducted to isotopically distinguish several types of groundwater that contributed to the hyporheic water in the study segment. There was a clear effect of altitude on the hydrogen/oxygen stable isotope ratios in the river water collected across the watershed. Groundwater unique both in chemical sand isotopic signatures in several spots occurred within the study segment, and its properties resembled to and its upwelling locations matched groundwater from a tributary river whose surface channel has disappeared 60 years ago. Positive numerical increases in abundance and/or a sign of nitrogen transfer in river riparian communities (algae, invertebrates, and riparian trees) originating from groundwater high in nitrate with elevated nitrogen stable isotope ratios were found. This study demonstrated that tributary groundwater with unique chemical properties manifested by an urban watershed river network continued to have cascading effects on biota across the river-riparian boundary in the mainstem river, even after urbanization transformed the tributary into a historically lost phantom river. We highlighted the legacy effects of landscape transformation in the subsurface domain and the significance of scrutinizing the past landscape and hydrological connectivity at the watershed scale in urban environments.

ecology↗

bioRxiv2023

Hot spots in a cold river synchronize temporarily separated salmon runs in their offsprings development

The identification of thermal heterogeneity in the environment and its inclusion in adaptive strategies are key to habitat management of cold-water fish, including salmonid species. This study tested the hypothesis that upwelling of groundwater (GW) from a tributary catchment through a relatively deep aquifer (tributary GW) affects salmon redds selection in an urbanized gravel-bed river, and that the spawning preference of such areas depends on the seasonal context. The field study was conducted between 2001 and 2015 in an approximately 6-km long segment of the Toyohira River, Northern Japan. Chum salmon redds distribution data over 15 years (2001-2015) were combined with spatial distribution data of hyporheic water affected by tributary GW in the riverbed to examine seasonally variable redds site selection in relation to the presence of unique GW. Furthermore, models that predicted the hyporheic water thermal regime were coupled with redds count data to estimate the approximate timing of fry emergence from the riverbed. The redds site selection was seasonally variable, with a higher dependence on tributary-GW-affected areas with a decrease in water temperature. The time until fry emergence from spawning was shortened when the tributary-GW area was chosen during the cold winter. Overall, the present study identified hotspots for salmon spawning redds in winter with a disproportionately high level of site selection because of their warmer temperature compared to surface river water in winter. Thermally diverse spawning habitats allow the diversification of spawner strains in synchronized descents to the sea. Signs of tributary-GW pollution was suggested, and thus the conservation of the groundwater pathway and its sources, followed by improvements in quality, can be beneficial to the Chum salmon populations in the Toyohira River.

ecology↗

bioRxiv2023

Cryptic connectivity between hyporheic and riparian zones via winged aquatic insects revealed by DNA barcoding

How subsurface hyporheic zone (HZ) of rivers is connected to riparian zones remains largely unknown. We collected benthic macroinvertebrates and adult aquatic insects for six years, including those at 30-cm depth in the HZ to identify insect taxa having a high level of habitat affinity for HZ (HZ taxa). Adults of HZ taxa were identified with the aid of CO1 gene barcoding, and the relative abundance of HZ taxa in the riparian zone was quantified. In addition to the previously known stonefly Alloperla ishikariana, three species of stonefly Leuctridae and one caddisfly species of Philopotamidae were identified as HZ taxa. At the annual scale, HZ taxa accounted for approximately 38% of the total aquatic insects in the family of stoneflies (Plecoptera), caddisflies (Trichoptera), and mayflies (Ephemeroptera) in abundance and 26% of biomass, with their seasonal peaks in early spring and mid-summer (60% in abundance and 47% in biomass). Few individuals of HZ taxa were found in benthic samples (<0.1%), and hyporheic samples quantified more but erroneously estimated relative abundances of adult HZ taxa, with Leuctridae and Philopotamidae being substantially underrepresented relative to their adult abundance. Cryptic biological connectivity between subsurface and riparian zones via winged HZ-taxa adults is substantial. DNA-based species identification combined with community surveys of adult HZ-taxa complementarily used with benthic data can substantially improve the effectiveness of biomonitoring programs and outcomes of habitat conservation based on more complete picture of ecosystem health.

ecology↗

bioRxiv2023

Does winterkill explain contrasting demographics of winter-breeding freshwater mussel populations in Ishikari River floodplain?

O_LIEnvironmental conditions bottlenecking species population demographics are less known in cold regions with harsh winters despite of global concerns of declining freshwater mussels (Unionidae). Few studies examined both cold and summer environments in attempts to promote habitat conservation of Unionidae species. C_LIO_LIWe identified the taxonomically confused Unionidae species using phylogenetic analysis with mtDNA (COI region) and tested the hypothesis that winter mortality is the main cause of contrasting population demographics and structures in floodplain lakes in northern Japan. Demographic surveys were conducted in two lakes, which contrasted in recruitment rates, over one year including 4-month ice-covered periods C_LIO_LIAlthough previous studies have identified freshwater mussels as introduced Anemina arcaeformis (Heude 1877) based on morphology, this study confirmed the focal species as potentially native Buldowskia iwakawai (Suzuki, 1939). High winter mortality (30-40%) of adult mussels was found, although the mortality did not significantly differ between the populations with contrasting recruitment. C_LIO_LISurprisingly, the annual mortality was much lower in juveniles (10%) than in gravid and nongravid adult individuals (40-75%). The main inter-population difference was attributed to the higher summer mortality of gravid females, but not juveniles and non-gravid individuals, in the population with low recruitment. C_LIO_LIThese results collectively suggest that summer hypoxia combined with physiological stresses on females in winter is a likely population growth-limiting mechanism. To prevent a chain of adult abundance decreases in winter and high mortality of gravid mussels and newly born juveniles in summer, improvements in summer habitat conditions are necessary, while winter conditions need to be considered simultaneously. Increases in water circulation rates and alleviations of hypoxic conditions is an option for short-term habitat improvement approach. The current study sheds light on the winter-mediated mortality of freshwater mussels in shallow eutrophic floodplain lakes and contributes to improved management strategies for degraded floodplain waterbodies. C_LI

ecology↗