Lake Hinuma Research Articles

Seasonal occurrence and food habits of larvae and juveniles of the threatened goby Gymnogobius castaneus in a salt marsh in Lake Hinuma, eastern Japan

Seasonal occurrence and food habits of larvae and juveniles of the threatened goby <i>Gymnogobius castaneus</i> in a salt marsh in Lake Hinuma, eastern Japan

ラムサール条約登録湿地「涸沼」に流入する涸沼川における コクチバスの侵入と再生産

ラムサール条約登録湿地「涸沼」に流入する涸沼川における コクチバスの侵入と再生産

Differences in fish assemblage structures between tidal marsh and bare sandy littoral habitats in a brackish water lake, eastern Japan

Fish assemblage structures and environmental properties (e.g., water quality, sediment condition and prey abundance) were compared between tidal marshes, dominated by the common reed Phragmites australis, and bare sandy areas in the brackish-water Lake Hinuma, eastern Japan, by daytime seine net sampling in October 2014, and January, April and July 2015. A total of 4,076 fish individuals from 30 species and 5,431 individuals from 23 species were collected in the tidal marshes and sandy areas, respectively. Higher species richness in the former habitat was due to the restricted occurrence of ten species, including threatened or near threatened, only to that habitat. Species composition and the abundances of several dominant species, such as the commercially important icefish Salangichthys microdon and the goby Acanthogobius lactipes, also differed between the two habitats, although no interhabitat differences in the mean species and individual numbers per haul were found. Moreover, the individual number of small benthic and epiphytic crustacean feeders, including A. lactipes, was greater in the tidal marshes than in the sandy areas, whereas zooplankton feeders, including S. microdon, showed the opposite pattern. Such interhabitat differences in fish assemblage structures may be partly related to food availability, sediment condition and/or the presence or absence of vegetative structures. Because each of the two habitats harbored a unique fish assemblage, conservation efforts for both habitats are important for enhancing overall fish species diversity and sustaining fishery resources in Lake Hinuma.

Comparison of predation risks for small fishes in salt marsh microhabitats in Lake Hinuma, eastern Japan, using tethering experiments

To clarify the role of salt marsh creeks as fish refuges, predation risks for two small species (the nektonic Oryzias latipes and benthic Acanthogobius lactipes) were compared among three microhabitats (upper and lower areas of a creek, and marsh edge separate from the creek) in a salt marsh in Lake Hinuma, eastern Japan, in July 2016, using daytime tethering experiments. The survival rate of O. latipes was highest in the upper creek (96%) and lowest at the marsh edge (62%), whereas no significant differences were found among the microhabitats for A. lactipes, with high survival rates (> 90%) in all microhabitats. Individual numbers of larger piscivorous fishes, determined by fyke net sampling, were greatest at the marsh edge, whereas no individuals were recorded in the upper creek, which was characterized by shallower depths and lower dissolved oxygen levels. The results suggested that the upper creek provides potential refugia for O. latipes, which occupied the upper and middle layers of the water column and exhibited hypoxia tolerance. The higher survival rate of benthic A. lactipes at the marsh edge may be due to their cryptic coloration in relation to bottom sediments, which helps them to avoid predation.

Oxidative stress responses to feeding activity and salinity level in brackish water clam Corbicula japonica

Three laboratory-scale experiments were conducted to assess the oxidative stress responses of brackish water clam Corbicula japonica to feeding activity and salinity level. Natural brackish water from Lake Hinuma was used in experiments I and II, while experiment III used artificial brackish water with cultured diatoms as the food source. During experiment I, the oxygen radical absorbance capacity (ORAC) varied greatly when the initial suspended solids (SS) concentration was 50 mg SS·L−1. As a result, no significant difference in ORAC was found between the initial SS concentrations of 5 and 50 mg SS·L−1 (p > 0.05). In contrast, during experiment II, ORAC decreased from 6.4 to 3.5 μmol Trolox Equivalent (TE)·mg protein−1 at the SS concentration of ~5 mg SS·L−1 (p < 0.05). The rate of carbon uptake in experiment I (SS concentration = 5 mg SS·L−1) was ~2.3 times greater than that in experiment II. These results indicate that SS availability has a great effect on ORAC in C. japonica. During experiment III, ORAC increased under initial SS concentrations of 0 and 40 mg SS·L−1 at salinities of 10 (p < 0.01) and 20 psu (p < 0.05), respectively. In contrast, ORAC decreased significantly decreased during the experiment for SS concentration = 80 mg SS·L−1 and salinity = 20 psu (p < 0.01) and for SS concentration = 120 mg SS·L−1 and salinity = 10 or 20 psu (p < 0.01); ATP content also decreased significantly (p < 0.01). A good correlation was found between the change in ATP content and ORAC. Together, the findings suggest that energy availability and salinity level have strong effects on antioxidant capacity in C. japonica.

Comparison of fish assemblage structures among microhabitats in a salt marsh in Lake Hinuma, eastern Japan

A total of 33 fish species, including commercially important and threatened species, were collected in three microhabitats (upper and lower areas of a small creek, and a marsh edge separate from the creek) of a salt marsh in Lake Hinuma, eastern Japan, in October 2014, and January, April and July 2015. Five species (Acanthogobius lactipes, Oryzias latipes, Mugil cephalus cephalus, Tribolodon brandtii and Salangichthys microdon) were dominant and accounted for 90.7% of the total number of individuals. The fish assemblage structures differed remarkably among the microhabitats, tending toward higher species and individual numbers on the marsh edge than in the upper creek. Species compositions also differed between the upper creek and the other microhabitats. Food availability (e.g., mysids, chironomid larvae and detritus) was considered to be a causative factor of the assemblage structure differences. In addition, microhabitat variations in water depth, dissolved oxygen level and bottom sediment, the upper creek being shallower with lower dissolved oxygen and higher sediment silt–clay proportion compared with the marsh edge, were also causative factors that indicated the importance of both biotic and abiotic environmental factors in the determination of fish distribution patterns across salt marsh microhabitats.

Changes in Salinity and Effects of the Great East Japan Earthquake on Water Quality in Brackish Lake Hinuma

Changes in Salinity and Effects of the Great East Japan Earthquake on Water Quality in Brackish Lake Hinuma

イトメTylorrhynchus heterochaetus QUATREFAGESの生態学的研究 1茨城県涸沼における生殖群泳

イトメTylorrhynchus heterochaetus QUATREFAGESの生態学的研究 1茨城県涸沼における生殖群泳

Food habits of salt marsh fishes in Lake Hinuma, Ibaraki Prefecture, central Japan

To determine the food habits of salt marsh fishes, the gut contents of 28 species, caught from a salt marsh in Lake Hinuma, Ibaraki Prefecture, central Japan, were investigated. Ontogenetic changes in diet were apparent in six species, including several of commercial importance (e.g., Acanthopagrus schlegelii and Hypomesus nipponensis). Smaller juveniles of such species fed mostly on planktonic copepods, with other prey items, including mysids, gammaridean amphipods and chironomid larvae, forming greater proportions in the diet of larger individuals. A cluster analysis based on dietary overlaps indicated that the salt marsh fish assemblage consisted of seven feeding guilds (small benthic and epiphytic crustacean, zooplankton, aquatic insect, polychaete, plant, terrestrial insect and detritus feeders). Among these, the first two guilds were the most abundantly represented in terms of species number, suggesting that small benthic and epiphytic crustaceans (e.g., mysids and gammaridean amphipods) and zooplankton (e.g., calanoid and cyclopoid copepods) were important food resources for the fish assemblage at the study site.

Dynamic changes in the accumulation of metabolites in brackish water clam Corbicula japonica associated with alternation of salinity.

The brackish water clam Corbicula japonica inhabits rivers and brackish waters throughout Japan where the major fishing grounds in the Ibaraki Prefecture, Japan, are located at the Hinuma Lake and Hinuma River. Water salinity in the Lake Hinuma is low and stable due to the long distance from the Pacific Ocean, whereas that in the downstream of the river varies daily due to a strong effect of tidal waters. In the present study, we dissected the gill and foot muscle of brackish water clam collected from these areas, and subjected them to metabolome analysis by capillary electrophoresis-time-of-flight mass spectrometry. More than 200 metabolites including free amino acids, peptides and organic acids were identified, and their amounts from the foot muscle tend to be higher than those from the gill. The principal component analysis revealed that the amount of each metabolite was different among sampling areas and between the gill and foot muscle, whereas no apparent differences were observed between male and female specimens. When the metabolites in the female clam at high salinity were compared with those at low salinity, concentrations of β-alanine, choline, γ-aminobutyric acid, ornithine and glycine betaine were found to be changed in association with salinity. We also compared various metabolites in relation to metabolic pathways, suggesting that many enzymes were involved in their changes depending on salinity.

涸沼親沢鼻の近年の変形と東北地方太平洋沖地震時の地盤沈下の影響

Ground subsidence by 22 cm occurred in Lake Hinuma in Ibaraki Prefecture during the 2011 Great Earthquake on March 11, 2011. This lake is connected to the Pacific Ocean via the Hinuma and Naka Rivers, resulting in the sudden increase in water level of the lake by 22 cm. This increase in water level was larger than the mean significant wave height of normal waves in Lake Hinuma, and thus large impact to the sandy beach and shoreline vegetation was caused. Field observations were carried out to investigate the impact as well as the impact of a groin constructed before the earthquake.

A NOTE ON LAKESHORE RESTORATION CREATING HABITAT OF PLANTS

A method for restoring the lakeshore using beach nourishment was studied, taking Lake Hinuma as an example. Field measurements on lakebed topography, grain sizes of bed materials, change in water level and salinity with time, and classification of lakeshore vegetations were carried out. Depth changes in median diameter of bed materials were measured. The content rate of fine sand had a peak approximately at the depth of closure due to waves, whereas the content rate of silt and clay and the salinity increased with the depth. The habitat of Brackish-water clam Corbicula japonica was located along the depth zone satisfying the condition that salinity is larger than 3 and bed materials are composed of fine sand. Using this information, the lakeshore restoration creating habitat of animals and plants could be done through the formation of a lakebed with a gentle slope using fine sand. A flat lakebed is formed first in the shallow water zone, and a barrier island is planned to be formed by wave action due to the shoreward sand movement. A wetland landward of this barrier is useful for the habitat of animals and plants.

Spatial distribution and assemblage structure of macrobenthic invertebrates in a brackish lake in relation to environmental variables

The distribution of organisms relative to their habitat is of central importance to ecology. The nature of this distribution provides an initial insight into the types of ecological processes that regulate populations and assemblages. Estuaries provide diverse habitats in terms of spatial heterogeneity in physical and chemical conditions. The purpose of the present study is to determine the assemblage structure and the spatial distribution of macrobenthic invertebrates in relation to environmental variables in a brackish lake, Lake Hinuma, in Japan. Thirty-seven sites in the lake were selected to cover the entire area of the lake along gradients for water depth, salinity and median grain size of sediment. A total of 23 species and five higher taxa groups were found. In terms of total individuals, Corbicula japonica, Prionospio japonica, Notomustus sp. and Einfeldia sp. were the most abundant species. The results of cluster analysis and canonical correspondence analysis using 14 dominant species revealed that median grain size and salinity have significant effects on the spatial distribution of 11 macrobenthic species. That is, the two species C. japonica and P. japonica were found at sites with larger grain size and higher salinity, the six species Gradidierella japonica, Assiminea lutea japonica, Tylorrhynchus heterochaetus, Cyathura sp., Melita sp. and Potamilla sp. were found at sites with smaller grain size and higher salinity, the one species Einfeldia sp. was found at sites with larger grain size and lower salinity, and the two species Polypedilum sp. and Notomustus sp. were found at sites with smaller grain size and lower salinity. The results demonstrated significant differences in macrobenthic assemblage structures along environmental gradients in a brackish lake.

SEDIMENT AND NUTRIENTS TRANSPORT IN THE HINUMA RIVER AND ESTUARY

Suspended sediment and nutrient transport were monitored during one year in two areas, one is the upper reach of a river which flow into Lake Hinuma, one is the estuary which is outlet of the lake. SS and particulate phosphorous (P-P) concentration can be estimated by turbidity using their correlation. The measurements of suspended load in the tidal channel were made using an acoustic Doppler current meter and turbidity meters. The amount of the sediment which is the difference between the sediment load monitored in the river and in the tidal channel during one year corresponds to the annual sedimentation rate in Lake Hinuma which was estimated by geological approach. The flux of P-P flow into the lake during floods reached 60% of the total phosphorous in one year. It is assumed that most of these P-P deposits in the lake and dissolved phosphorous released from P-P makes phytoplankton grow up.

Natural hybridization and gene flow between twotridentiger gobies in lake hinuma (ibaraki prefecture, japan)

Of 851 specimens ofTridentiger obscurus andt. brevispinis collected from Lake Hinuma (Ibaraki Prefecture, Japan) from July 1996 to February 1998, 49 (5.8%) comprised F1 hybrids and backcross progeny of the two species. Since the mitochondrial DNA haplotypes of the F1 hybrids reflected those ofT. brevispinis, most instances of hybridization are thought to have occurred between maleT. obscurus and femaleT. brevispinis. Although both allozyme and mitochondrial DNA analyses indicated backcrossing and introgression of mitochondrial DNA, the frequency of backcross progeny was relatively low, suggesting the existence of a natural selection to backrossing.

In situ measurement of productivity and respiration in aquatic systems by a new box incubation method

Changes in productivity and community respiration rates were assessed hourly through 24 and 29-h periods in Lake Hinuma, and every 1.5 h in Hiroshima Bay through a 25-h period, using a newly developed box incubation and free water method. The design of the box included light and dark bottles, with simultaneous measurement of temperature, DO and pH of the water in light and dark boxes, in which the water was exchanged with outside water, at intervals of 1 h (Lake Hinuma) and 1.5 h (Hiroshima Bay), respectively. Most changes in DO and DIC, during their respective incubations, were better approximated by linear, rather than exponential, models. During daylight, increased rates of DO in the light box ranged from 0.34 to 45.0 μmol l−1h−1 (Lake Hinuma) and 0.11 to 4.1 μmol l−1h−1(Hiroshima Bay), compared with decreased rates of DO from 0.20 to 17.0 μmol l−1h−1 (Lake Hinuma) and 0.25 to 3.2 μmol l−1h−1 (Hiroshima Bay) in the dark box. In contrast, the DO decrease rates in both light and dark boxes during nighttime ranged from 1.3 to 7.7 μmol l−1h−1 and 0.38 to 9.6 μmol l−1h−1 (Lake Hinuma), and from 0.10 to 1.0 μmol l−1h−1 and 0.30 to 0.80 μmol l−1h−1 (Hiroshima Bay), respectively; they nearly coincided for almost all periods. Metabolic Quotients (the ratio of DO to DIC change) were in the range from 0.61 to 1.35 (the 25th to 75th) (period-1) and 0.99 to 1.86 (period-2), respectively, except for a few incubation periods in the early night and morning hours. Most of the changes in the light box coincided with those in free water, indicating that the rate of change in the box was equal to that in the lake. However, due to advection, the free water outputs sometimes differed from those of the box incubation. We conclude that the box method is capable of evaluating gross and net production, and respiration, in a wide variety of aquatics with limited effort and time.

Temporal utilization of a brackish water lake, Lake Hinuma, as a nursery ground by amphidromous ayu, Plecoglossus altivelis (Plecoglossidae) larvae

A study was conducted in Lake Hinuma, northern central Japan, in order to elucidate the role of a brackish water lake in the early life history of amphidromous ayu, Plecoglossus altivelis (Plecoglossidae). Descriptions of amphidromous P. altivelis larvae based on wild specimens are also given. Larvae first appeared in Lake Hinuma in October and remained inside the lake until December. During this period, continuous recruitment of newly hatched yolk-sac larvae was observed. The size of larvae found in the system ranged from 5.2–32.1 mm SL, representing the entire larval period of the species, from the newly hatched yolk-sac larvae to metamorphosed juveniles. Larvae emigrated out of the Lake Hinuma system to the coastal waters after the surface water temperature of the lake dropped below 6° C and became lower than that of adjacent coastal waters. It is concluded that brackish water lakes play an important role in the early life history of amphidromous P. altivelis, as a temporary nursery ground.

A note on beach changes around Oyazawabana sand spit in Lake Hinuma

A note on beach changes around Oyazawabana sand spit in Lake Hinuma

ひ沼におけるフォールアウト核種の移行挙動に関する研究 （Ｉ）

Deposition of 134Cs, 137Cs and other fallout nuclides was observed at PNC O-arai Engineering Center in May 1986 after Chernobyl accident. The fallout radionuclides, especially 90Sr and 137Cs in lake water, sediments and fish have been measured in Lake Hinuma located 2km north-west of the Center since 1986 in order to investigate migration behavior of these nuclides in lake ecosystem. In August 1986, the 137Cs in sediments was irregularly distributed at each sampling point in Lake Hinuma. It was different from distributions of 239, 240Pu and 241Am, which showed that concentrations at center of the lake were higher than that near the shore in 1986. Horizontal distributions of 137Cs in sediments then shifted to similar distribution of 239, 240Pu by 1989. The 137Cs concentrations in sediment showed a tendency to increase slightly in 1987 and 1988 and then to decrease. An apparent half-life of 137Cs in sediment was derived from field data as approximately 3 years. Distribution coefficient (Kd) for 90Sr in sediments, a ratio of the concentration of 90Sr in dry sediment to that in water, was approximately 90(l/kg) as 50% value in cumulative probability distribution of observed KdS. Concentration Factors (CFs) for 90Sr were from 4 to 45(l/kg) in edible parts of fishes (Haze, Ugui and Wakasagi).

Life History of Shirauo Salangichthys microdon; Salangidae in a Brackish Lake, Lake Hinuma, Japan.

Shirauo S. microdon Bleeker: Salangidae is a very popular food fish, inhabiting brackish waters throughout Japan. However, little is known regarding the life cycle of the species. A 2-year survey was conducted to clarify the movement and dispersal of S. microdon throughout its life history in Lake Hinuma, a brackish lake in central Japan. Results of the survey revealed that from emergence in spring to maturation and spawning the following spring, S. microdon was found within Lake Hinuma all year round. Although there are seasonal occurrences of the species in Shimohinuma River, a river flowing out of Lake Hinuma, when the river shows a well-mixed vertical profile, S. microdon was not found in coastal waters adjacent to the lake, disproving any diadromous life history of the species. Comparisons of standard length, body weight and gonadosomatic index of S. microdon caught within the lake and in the river did not show any significant differences. It was concluded that S. microdon is dependent upon the brackish environment, undertaking its complete life history within the Lake Hinuma water system. This small species is one of the few brackish water species in Japanese waters.