Lake In Japan Research Articles

The hybrid origin of Potamogeton biwaensis Miki, an endemic submerged plant in Lake Biwa, Japan

Lake Biwa is the largest lake in Japan, and is known to have an ancient origin. The flora and fauna of this lake are characterized by high levels of endemism. Potamogeton biwaensis Miki (Potamogetonaceae) is one of two macrophyte species endemic to Lake Biwa. In the present study, we concluded based on DNA evidence that P. biwaensis is a hybrid between P. wrightii and P. maackianus. Recently, the populations of P. biwaensis have declined, and continuous monitoring is important for the conservation of this endemic macrophyte.

Complete F mitochondrial genomes of the Biwa pearl mussel, Hyriopsis schlegelii: the first report from the species’ native lake in Japan

We determined two complete mitochondrial sequences of female-transmitted (F) mitogenomes of two Hyriopsis schlegelii specimens from this species’ original habitat, Lake Biwa. The mitogenomes were both 15,951 bp in length, and the gene contents and orders agreed with those of the typical F mitogenome of Hyriopsis. Molecular phylogenetic analysis based on the previously identified 13 partial sequences confirmed that the two mitogenomes both belonged to H. schlegelii and not to a closely related Chinese species, Hyriopsis cumingii. The same analysis revealed that two mitogenomes (HQ641406 and FJ529186) previously published as H. schlegelii and H. cumingii might be misidentified.

Environmental DNA reveals nonmigratory individuals of Palaemon paucidens overwintering in Lake Biwa shallow waters

AbstractIn Lake Biwa, the largest freshwater lake in Japan, the lacustrine shrimp Palaemon paucidens has been reported to undertake seasonal migrations, living in deep waters from autumn to winter ...

NUMERICAL ASSESSMENT OF THE IMPACT OF STRONG WIND ON THERMAL STRATIFICATION IN LAKE BIWA, JAPAN

Water temperature near the surface of a lake increases with increasing air temperature, whichresults in stratification. The strength of stratification substantially influences the transport of dissolved oxygenfrom the surface to the bottom water of a lake. In recent years, the decrease in dissolved oxygen at the bottom ofthe northern part of the Lake Biwa, the largest freshwater lake in Japan, has been observed. The main cause ofthis is considered to be the change in stratification, which depends on weather and climate conditions. In thepresent study, numerical simulations were carried out to investigate the effect of strong wind on the structure ofstratification in Lake Biwa. The baseline simulation was conducted using actual meteorological data, andexperimental simulations were conducted using meteorological data with modified wind speed and direction.The numerical experiments showed that if the magnitude of the wind is strong enough, the stratificationcollapses and the wind can enhance the vertical mixing in the bottom layer even in the summer season withstrong thermal stratification. In a stratified season, when the strong wind blows predominantly in one direction,the rate of the vertical mixing changes by the wind direction. Moreover, as the duration of the strong windextends, vertical mixing easily occurs.

Evaluation of Thermal Stratification and Flow Field Reproduced by a Three-Dimensional Hydrodynamic Model in Lake Biwa, Japan

Water temperature near the surface of a lake increases with increasing air temperature, which results in stratification. The strength of stratification substantially influences the transport of water parcels from the surface to the bottom of a lake. In recent years, the stratification in Lake Biwa—the largest freshwater lake in Japan—has been stronger. However, it is difficult to reproduce the stratification well in the simulations. In the present study, we built a hydrodynamic model for the purpose of analyzing the structure of the stratification in detail. Using the model, we evaluated the reproducibility of the seasonal and annual changes of vertical water distribution and flow field in Lake Biwa from 2007 to 2011. The hydrodynamic model results show that the vertical water distribution approximately agrees with the field observations based on the statistical analysis. The seasonal change of thermal stratification is reasonably reproduced by the hydrodynamic model simulations. In the simulation, there are mainly two circulation flows at the surface layer of the lake. The first flows anticlockwise and the second flows clockwise in the northern part of Lake Biwa. In order to compensate for the surface water flow, the water under the thermocline sometimes flows in the opposite direction under each circulation flow.

Acidocella aquatica sp. nov., a novel acidophilic heterotrophic bacterium isolated from a freshwater lake.

A novel acidophilic heterotrophic bacterium, strain Ok2GT, was isolated from a freshwater lake in Japan. Cells of the isolate were Gram-stain-negative and non-motile rods (0.6-0.8×1.0-2.8 µm). Growth was observed at 4-35 °C with an optimum growth temperature of 28 °C. The pH range for growth was 3.0-6.2 with an optimum pH of 4.5. The strain utilized fructose, glucose, sucrose, mannitol, sorbitol, ethanol, benzyl alcohol, pyruvate, yeast extract and tryptone as carbon and energy sources for aerobic growth. DNA G+C content was 62.6 mol%. The major cellular fatty acid and the isoprenoid quinone were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and Q-10, respectively. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain Ok2GT belongs to the genus Acidocella but is distinct from existing species with sequence similarities lower than 97 %. On the basis of these results, strain Ok2GT (=NBRC 112502T=DSM 104037T) is proposed as the type strain of a novel species, Acidocellaaquatica sp. nov.

4 海跡湖の湖岸・海底の微地形分類を基礎とした湖沼環境の変化

4 海跡湖の湖岸・海底の微地形分類を基礎とした湖沼環境の変化

Spatial genetic structure and body size divergence in endangered Gymnogobius isaza in ancient Lake Biwa

Gymnogobius isaza is a freshwater goby endemic to ancient Lake Biwa, the largest lake in Japan. The species is now listed as ‘Critically Endangered’ in the Red Data Book of Japan. Nevertheless, it remains subject to fishing without any specific management strategies. Previous studies using mitochondrial DNA markers showed that this fish species has two cryptic lineages. However, little is known about spatial genetic structure and ecological differences across the broad lakescape. In this study, we collected fish samples at nine locations along the lakeshore during the breeding season and tested for the presence of spatial heterogeneity in the lineage’s composition while measuring body size as the most fundamental biological trait. The results showed that the major lineage dominated all the sampling locations whereas the minor lineage consisted of only 11% (16/143) of samples. Furthermore, although their spatial distributions overlapped (i.e. the two lineages may be well mixed), we found it possible that the minor lineage may have a potentially narrower distribution than the major lineage. In addition, we found that the two lineages differ in body size; specifically, the minor lineage is smaller in size. From the viewpoint of genetic diversity conservation and sustainable resource use, this fish should be managed as two genetic stocks and spatial and/or body size-based fishery management is desirable, with particular attention to the minor (smaller sized) lineage.

Phytoplankton species abundance in Lake Inba (Japan) from 1986 to 2016

AbstractLake Inba is one of the most eutrophic lakes in Japan. This data paper reports the abundance of phytoplankton species sampled biweekly from April 1986 to March 2016 at four stations in Lake Inba. Monitoring has been carried out by Chiba Prefectural Government, and phytoplankton count data have been collected since 1986. A total of 340 phytoplankton species were identified and enumerated by microscopy, as numbers of cells or colonies. The abundance of each species was expressed as cells per milliliter lake water. Total cell density ranged from 102 to 108 cells ml−1. The dominant cell class density was Cyanobacteria throughout the year. Cyanobacteria, such as Phormidium spp., Microcystis aeruginosa, and Anabaena spp. (Dolicospermum spp.), were the most dense in all months. The dominant cyanobacteria species reached concentrations of 107 cells ml−1. Diatoms, such as Aulacoseira granulata and A. ambigua, were also abundant, reaching 106 cells ml−1. These data can be used to appreciate how anthropogenic disturbances, such as eutrophication and global warming, affect density and community composition of phytoplankton.

Residents’ concerns about lake uses and environments: a comparative study of Lakes Kasumigaura, Suwa, and Biwa in Japan

Lakes are a common water resource. This study analyzed residents’ concerns regarding their lake environments to help solve lake environmental problems. The study area comprised three lakes in Japan—Kasumigaura, Suwa, and Biwa—which have different tendencies to change in water quality. A sample of 1200 respondents was evenly distributed among the three lake regions. A questionnaire survey asked about respondents’ proximity to the lake, their concerns about the lakes’ uses and environments, their evaluations of the lakes, and their opinions regarding environmental improvements. The number of options chosen in response to the multiple-answer questions was used to measure the extent of concern. The results found that knowledge of the water environment, general environmental concerns, the amount of travel time to the lake, and the visiting interval were significantly related to concerns about the lake environment. The results of logistic regression analysis found that high environmental concerns positively influenced attitudes toward lake use. Ways to increase concerns for lake environmental problems and the relationship between concerns and attitudes toward solving lake environmental problems are discussed.

Susy, Seascan, and other acoustical contraptions

In the early 1990s, the acoustical oceanography research group, led by Dr. David Farmer, developed several high-frequency sonar platforms for near-surface oceanography. These platforms, suspended approximately 25 m below the surface, typically supported six frequencies of upward-looking echo-sounders and up to four steerable 100 kHz sidescan sonars. Additionally, the SUSY platform had four extensible arms, 4.5 m in length, each supporting a wideband hydrophone. The platforms had sufficient batteries and data recording for up to 40 hours of autonomous operation, which could be extended through scheduled on/off periods. The intent of these platforms was to investigate properties of near-surface bubble due to breaking waves, with additional Doppler velocity measurements of surface waves and convective circulations. These platforms were also used for other studies, such as tidal convergence zones and ship wakes. The SEACAN platform was also used to assess zooplankton and fish populations in lake in Japan. This presentation will review key field trials and scientific achievements generated through use of these platforms.

Molecular phylogeny and taxonomic revision of the genus Wittrockiella (Pithophoraceae, Cladophorales), including the descriptions of W.australis sp. nov. and W.zosterae sp. nov.

Wittrockiella is a small genus of filamentous green algae that occurs in habitats with reduced or fluctuating salinities. Many aspects of the basic biology of these algae are still unknown and the phylogenetic relationships within the genus have not been fully explored. We provide a phylogeny based on three ribosomal markers (ITS, LSU, and SSU rDNA) of the genus, including broad intraspecific sampling for W.lyallii and W.salina, recommendations for the use of existing names are made, and highlight aspects of their physiology and life cycle. Molecular data indicate that there are five species of Wittrockiella. Two new species, W.australis and W.zosterae, are described, both are endophytes. Although W.lyallii and W.salina can be identified morphologically, there are no diagnostic morphological characters to distinguish between W.amphibia, W.australis, and W.zosterae. A range of low molecular weight carbohydrates were analyzed but proved to not be taxonomically informative. The distribution range of W.salina is extended to the Northern Hemisphere as this species has been found in brackish lakes in Japan. Furthermore, it is shown that there are no grounds to recognize W.salina var. kraftii, which was described as an endemic variety from a freshwater habitat on Lord Howe Island, Australia. Culture experiments indicate that W.australis has a preference for growth in lower salinities over full seawater. For W.amphibia and W.zosterae, sexual reproduction is documented, and the split of these species is possibly attributable to polyploidization.

Draft Genome Sequences of Tersicoccus phoenicis DSM 30849T, Isolated from a Cleanroom for Spacecraft Assembly, and Tersicoccus sp. Strain Bi-70, Isolated from a Freshwater Lake.

ABSTRACTHere, we report the draft genome sequences of Tersicoccus phoenicis DSM 30849T, isolated from a spacecraft assembly cleanroom at the National Aeronautics and Space Administration (NASA), and Tersicoccus sp. strain Bi-70, isolated from Lake Biwa, the largest lake in Japan. These genome sequences facilitate our understanding of the adaptation of these closely related strains to different habitats.

Genetic diversity of common carp (Cyprinus carpio L.) strains breed in Poland based on microsatellite, AFLP, and mtDNA genotype data

The common carp (Cyprinus carpio L.) has a long-standing history in Polish pond aquaculture, which has given rise to a great number of local breeds, strains and hatchery populations. They are well adapted to their local conditions, play an important role for fisherman's livelihoods and embody valuable genetics for future breeding programs. Proper maintenance of animal genetic resources (AnGR) requires an appropriate strategy based upon the precise knowledge of their genetic structure. This study genetically characterizes 20 common carp strains breed in Poland alongside with wild carp from Onuma Lake in Japan. We study three different types of genetic markers including the 963 AFLP markers, a set of 11 microsatellite loci (STR) and DNA sequences of the mitochondrial control region (D-loop). Bayesian clustering analysis of microsatellite loci divided the studied strains into 17 distinct clusters. Using population assignment test 92.4% of carp individuals were correctly assigned to their strain of origin. Microsatellite and AFLP marker analysis have shown the moderate but significant level of genetic variation between strains (AMOVA 23% and 18.2% respectively). AFLP and STR analysis of genetic distances gave equivalent values and were positively correlated with high values of the Mantel test (r=0.553, n=20, p=0.001). Only two mtDNA haplotypes (H5 and H2) were detected in all studied carp strains with H2 being the most prevalent.This is the first comprehensive genetic research of common carp strains breed in Poland which provided crucial data for the national conservation strategy. This study means that this resource can now be placed within the context of similar studies worldwide allowing the further improvement and breeding work.

Diversification of mitochondrial genome of Daphnia galeata (Cladocera, Crustacea): Comparison with phylogenetic consideration of the complete sequences of clones isolated from five lakes in Japan

To characterize genetic diversity and gene flow among Daphnia galeata populations, the complete nucleotide (nt) sequences of the mitochondrial (mt) DNAs of D. galeata clones isolated from five lakes in Japan (Lakes Shirakaba, Suwa, Kizaki, Kasumigaura, and Biwa) were determined. Comparison of non-synonymous (amino acid altering) substitution rates with synonymous substitution rates of D. galeata mt protein-coding genes demonstrated that ATPase8 and COI genes were the most and least susceptible, respectively, to the evolutional forces selecting the aa substitutions. Several non-synonymous substitutions were found in ATPase8 and ATPase6 even in the comparison that no synonymous substitution was found. Comparison of the total number of nt variations among the mt DNAs suggested the phylogenetic relationship ((((Shirakaba/Suwa, Kizaki), Kasumigaura), Biwa), D. pulex). Maximum-likelihood analysis using the total nt sequences of mt protein-coding genes confirmed this relationship with bootstrap values higher than 98%. All the mtDNAs of the analyzed Japanese D. galeata clones contained a control region of essentially the same structure that is distinct from those of the previously reported European Daphnia species of the D. longispina complex. The two control regions of different structures spread among mtDNAs of the Japanese and European Daphnia species, respectively, probably after the divergence of the Japanese D. galeata under different selection pressures associated with their habitats.

The Effect of Charophyte Communities on Phosphorus Flow in Lake Shinji, Japan

Charophytes are a group of aquatic algae similar to vascular plants; they play an important role in the nutrient cycling of lakes. Specifically, under eutrophication, charophytes have a greater capacity for phosphorus accumulation than vascular plants. During their development, charophytes accumulate calcium within their structures, along with dissolved phosphorus from the water column. The calcified structures are deposited onto the lakebed after the death of the plant, with phosphorus co-precipitating with calcium, limiting its return to the water. Lake Shinji is one of many lakes in Japan where the charophyte population is in decline or extinct. Using aerial photographs acquired 70 years ago, we estimate the extent of the historical charophyte community in Lake Shinji, and quantitatively evaluate and examine the extent to which charophytes accumulated phosphorus in the lake sediment. The amount of phosphorus accumulated by the charophyte community in Lake Shinji is estimated to be 0.56-25.5 t P y-1. Charophytes are not found in Lake Shinji today, and although various species of vascular plants have recolonised the lake, no significant improvement in water transparency has been observed. This study concludes that charophytes are likely to be a more effective measure in combating eutrophication than vascular plants.

Growth rates and tolerance to low water temperatures of freshwater bacterioplankton strains: ecological insights from shallow hypereutrophic lakes in Japan

To investigate differences in culturable freshwater bacterioplankton between summer and winter, we examined specific bacterioplankton in the low temperature surface water of two shallow, hypereutrophic, temperate lakes in Japan over two winters, and compared our results with the previously published data. We used the size-exclusion assay method (SEAM), a cultivation-based approach that simply and effectively isolates typical freshwater bacterioplankton. The specific clusters detected in the winter samples were the Rhodoferax sp. BAL47 cluster (LimA and LimC), a predominant and ubiquitous freshwater lineage, and the LiUU-5-340 cluster. To confirm tolerance to low water temperature of winter-specific groups, we also compared growth rates at 5°C among several pure strains of typical freshwater bacterioplankton clusters belonging to the Rhodoferax sp. BAL47, Polynucleobacter necessarius, GKS98, LiUU-5-340, and IRD18C08 of the class Betaproteobacteria, and the Luna-1 and Luna-2 of the class Actinobacteria. Specific detectability of freshwater bacterioplankton clusters/subclusters by SEAM in the winter sample substantially correlated with the low temperature-specific growth characteristics of each isolate. Response to water temperature is a key control factor in freshwater bacterioplankton assemblage composition. These results provide important insights into the specific response to water temperature of several ubiquitous culturable freshwater bacterioplankton clusters inhabiting a temperate climate zone.

Variations in lignin-derived phenols in sediments of Japanese lakes over the last century and their relation to watershed vegetation

Lignins have been used as a biomarker to explore changes in terrestrial organic matter input into lakes and to investigate past watershed vegetation. Burial of organic carbon (OC) in lake sediments, an important component of the global C cycle, is likely associated with the terrestrial OC input. However, few studies have explored changes in terrestrial C input into lakes in the last century. Furthermore, the relationship between lignin phenol compositions and watershed vegetation remains poorly examined. In this study, we examined changes in OC concentrations, OC mass accumulation rates (MAR), and lignin phenol compositions over the last century in sediments from six lakes in Japan that differ in watershed land-use and vegetation. The sediments were dated using 210Pb and 137Cs, and showed increased OC concentrations and MARs in three lowland lakes over the last century. This pattern was not found in three mountain lakes. In one of the lowland lakes, lignin phenol concentrations normalized to OC did not change during the periods with high OC concentrations and MARs. This indicates that not only eutrophication but also enhanced terrestrial OC input could lead to greater burial of OC. The lignin phenol compositions did not show clear trends over the last century in most of the lakes examined. The ratios of syringyl to vanillyl phenols and the lignin phenol vegetation index had significant relationships with proportions of angiosperms in watershed vegetation. These results demonstrate that lignin phenols are useful in inferring recent as well as past changes in lake watershed environments.

Zooplankton abundance in the pelagic region of Lake Kasumigaura (Japan): monthly data since 1980

AbstractMicroscopic crustaceans (cladocerans and copepods) and rotifers are the principal zooplankton components of the pelagic food webs in lakes. They play important ecological roles, functioning as essential links between primary producers and planktivorous fish. Individuals zooplankton are important nodes of matter flow in pelagic ecosystems. The zooplankton community structure can provide useful indicators of top–down processes, such as the magnitude or strength of planktivorous predators and the extent of zooplankton grazing. Here we report the abundance of zooplankton taxa (crustaceans and rotifers) that were recorded monthly, from January 1980 to September 2015, at two stations on Lake Kasumigaura, a shallow eutrophic lake that is the second largest lake in Japan. The data include information on 12 copepod species (taxa), 20 cladoceran species (taxa), 40 rotifer species (taxa), and the opossum shrimp (Neomysis intermedia). In the 1980s, the plankton of the lake were characterized by cyanobacterial blooms and the co‐dominance of Bosmina and Diaphanosoma in the summer. In addition, the two cladoceran genera, Daphnia galeata and Chydorus sphaericus were often prominent. The plankton profile changed dramatically in the middle (1997–2004) of the present long‐term monitoring period, when cyanobacteria disappeared and diatoms became dominant even in the summer; concurrently, only the Diaphanosoma cladocerans were evident. However, in the past 10 years, cyanobacterial blooms, the co‐dominance of Bosmina and Diaphanosoma, and D. galeata have re‐emerged. Zooplankton monitoring forms part of the Lake Kasumigaura Long‐Term Environmental Monitoring Program, which has been conducted by the National Institute for Environmental Studies (NIES) since 1977. Data on other planktonic components (phytoplankton and the elements of microbial food webs) noted during monitoring and on primary production were published in Takamura and Nakagawa (Ecol Res 27:8392012a, Ecol Res 27:837 2012b, Ecol Res 31:287 2016). Lake Kasumigaura is a core site of the Japan Long‐term Ecological Research Network, a member of the International Long‐term Ecological Research Network. Our quantitative dataset spanning several decades is unique in terms of the work on lakes and the plankton therein, and is freely available. The dataset has been used in ecological and environmental programs, as well as in studies on lake management.

Sulfuriflexusmobilis gen. nov., sp. nov., a sulfur-oxidizing bacterium isolated from a brackish lake sediment.

A chemolithotrophic sulfur-oxidizing bacterium, strain aks1T, was isolated from sediment of a brackish lake in Japan. The cells were curved rod-shaped and Gram-stain-negative. The G+C content of the genomic DNA was 53 mol%. The major components in the cellular fatty acid profile were C16 : 0 and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). As electron donor for chemolithoautotrophic growth, strain aks1T oxidized thiosulfate, sulfide, and elemental sulfur. The strain could utilize oxygen and nitrate as an electron acceptor for thiosulfate oxidation. Growth was observed at a temperature range of 5-34 °C, with optimum growth at 30-32 °C. Growth of the strain was observed at a pH range of 6.4-8.7. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain is related to members of the family Granulosicoccaceae within the order Chromatiales, with sequence similarities around 92 %. On the basis of phylogenetic and phenotypic properties, strain aks1T represents a novel species of a new genus, for which the name Sulfuriflexus mobilis gen. nov., sp. nov. is proposed. The type strain of the type species is aks1T (=DSM 102939T=NBRC 111889T).