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Three preparation methods for the identification of diatom flora at a river mouth tidal flat were evaluated in terms of species richness, diversity, and composition using a conventional acid-cleaning method, a nuclear staining method, and a newly introduced sieving method. Twenty-five diatom samples were collected from Fujimae Tidal Flat sediments, Nagoya, Japan, in July 2014. Three methods respectively showed different aspects of the diatom flora. The acid-cleaning method indicated the highest species diversity, but it extracted dead diatoms with living ones indiscriminately. In comparison with the acid-cleaning method, the staining method effectively extracted diatoms with fragile and small-sized cells. The sieving method scraped the sessile diatoms selectively and supplemented the staining method in which sessile diatoms were mostly neglected. A combination of these three methods enables to describe precise diatom flora of a tidal flat.

A new diatom species Gomphosphenia biwaensis Ohtsuka & D.Nakai was described from the south basin of Lake Biwa in Central Japan. Scanning electron microscopy revealed that the fine structure of this species is typical of the genus Gomphosphenia, although the striae are composed of a few areolae unlike Gomphosphenia lingulatiformis, the type species of the genus. Based on light micrographs of more than 100 specimens, the radii of the head pole, foot pole, and each valve side of these specimens were measured within a range that can be approximated by an arc, as well as the valve length, width, and stria density. The morphometric data were log-transformed and orthogonalized using principal component analysis based on the correlation coefficient, and the first principal component was eliminated to remove the effect of size differences. The second and subsequent principal components approximately followed a multivariate normal distribution. Morphometric data of the specimens from the other samples from Lake Bi...

Microhabitat-level spatial variations in diatom and isotope compositions of epilithic periphyton in the littoral zones of Lake Malawi were examined using periphyton samples collected from seven regions of the lake. Discriminant analysis revealed a clear difference in diatom composition among the slopes of the rocks from which the samples were collected. This difference may be associated with interspecific variation in the adhesive power of diatoms. The slope of the rocks also strongly affected the stable carbon isotope ratios of periphyton, together with subsidiary effects of algae size class, sampling site, depth, and some of their interaction terms. The effect of slope can be explained by the decrease in photosynthetic activity along the slope, which originates from the decline in sunlight. Thus, the diatom composition and carbon isotope ratios may be good indicators of microhabitat and have the potential to be powerful tools for quantitative measurement of microhabitat utilization of epilithic algae-feeding consumers of this lake, including territorial cichlids.

Summary Based on epilithic diatom samples collected from the rocky littoral zone of Lake Malawi (102 diatom taxa belonging to 34 genera were listed in the Supporting Information) we proposed the transfer of three taxa to new genera. Afrocymbella brunii (Fricke) comb. nov. was transferred from Gomphonema because of its dorsiventral valve and its transapically elongated dorsal stigma. Afrocymbella rossii (Kociolek & Stoermer) comb. nov. was also transferred from Gomphocymbella, which is actually a synonym of Gomphonema. Aulacoseira euareolata (O.Muller) comb. nov. et nom. nov. was transferred from Melosira because of the presence of linking spines and mantle areolae, and its specific epithet was replaced because of homonymy with Aulacoseira areolata Moisseeva.

We present a short note on the species composition of testate amoebae in a poor fen on mineral soil near the Pacific Coast in the hilly area of Central Honshu, Japan. In total 45 species and subspecific taxa belonged to 21 genera and 14 families of testate amoebae were recorded. Eight species and nine subspecies are newly recorded from Japan. However, most species from the list can be considered as distributed worldwide and associated mostly to oligotrophic/acid Sphagnum conditions.

This article describes a new diatom genus Moreneis from the Yellow Sea sand flats on the west coast of Korea. The new genus is characterized by a unique combination of morphological characteristics, including the shape of the plastids, which have not been previously observed in diatoms. The valve morphology resembles other genera belonging to Lyrellaceae, within which we place this genus. In terms of areolae structure, Moreneis resembles Petroneis and Placoneis; however, it differs from both genera with respect to the raphe system and plastid shape. Cells of Moreneis spp. have a single large plastid appressed to the girdle of the secondary side of the valve, with two lobes extended toward the primary side of the valve. Furthermore, the unique feature of Moreneis frustules is the raphe, which has both external central and apical endings bent in opposite directions. We differentiated four taxa, which we describe as new for science. However, based on our findings, several established species from Navicula should also be formally transferred to Moreneis, including N. alpha Cleve, N. besarensis Giffen, N. epsilon Cleve, N. menaiana Hendey, N. polae Heiden, and N. quadri-undulata F. Meister. Analysis of published data revealed that species belonging to Moreneis are numerous in tropical marine littoral waters, and in moderate climate zones, especially in the western Pacific, with only a few species occurring in the Mediterranean and Atlantic.

This article describes a new diatom genus Moreneis from the Yellow Sea sand flats on the west coast of Korea. The new genus is characterized by a unique combination of morphological characteristics, including the shape of the plastids, which have not been previously observed in diatoms. The valve morphology resembles other genera belonging to Lyrellaceae, within which we place this genus. In terms of areolae structure, Moreneis resembles Petroneis and Placoneis; however, it differs from both genera with respect to the raphe system and plastid shape. Cells of Moreneis spp. have a single large plastid appressed to the girdle of the secondary side of the valve, with two lobes extended toward the primary side of the valve. Furthermore, the unique feature of Moreneis frustules is the raphe, which has both external central and apical endings bent in opposite directions. We differentiated four taxa, which we describe as new for science. However, based on our findings, several established species from Navicula should also be formally transferred to Moreneis, including N. alpha Cleve, N. besarensis Giffen, N. epsilon Cleve, N. menaiana Hendey, N. polae Heiden, and N. quadri-undulata F. Meister. Analysis of published data revealed that species belonging to Moreneis are numerous in tropical marine littoral waters, and in moderate climate zones, especially in the western Pacific, with only a few species occurring in the Mediterranean and Atlantic.

Effects of fish predation propagate through aquatic food webs, where the classical grazing food chain and microbial loop are interwoven by trophic interactions. The overall impact on aquatic food webs is further complicated because fish may also exert bottom-up controls through nutrient regeneration. Yet, we still have limited information about cascading effects among fish, zooplankton, phytoplankton, and microbes. In this study, we performed a mesocosm experiment to evaluate effects of fish introduction on plankton communities. Six plots were set in factorial combination with fish introduction and rice straw plowing in a paddy field, and the experiment was continued for 4 weeks. Introduction of fish significantly increased chlorophyll a concentrations in smaller size fractions ( 5 μm in length) and heterotrophic nanoflagellates in 3–15 μm fraction. Microbes in 0.8–3 μm fraction showed increasing but not significant trends in response to fish introduction. These results indicate cascading effects of fish predation operating via two pathways, one through grazing food chain and the other through microbial food web. Phytoplankton community compositions shifted in similar fashion in all plots until 1 week after fish introduction, and then diverged between plots with and without fish thereafter. Bottom-up effects of fish introduction were suggested by increases of total chlorophyll a and inedible phytoplankton species in response to fish introduction. This study provides an example of how fish predation regulates biomass and structure of phytoplankton and microbial communities.

We examined the effects of predation by Nigorobuna Carassius auratus grandoculis larvae and fry, a crucian carp endemic to Lake Biwa, Japan, on the community structure of aquatic organisms in rice fields. Six experimental plots with three different rice-straw treatments in the presence/absence of stocked larvae were prepared. In each plot, the number of aquatic organisms ranging in size from 30 μm to 5 mm in the water, as well as those from 63 μm to 5 mm in size in the surface sediments, was surveyed 6, 13, 20, 26, 34, and 41 days after the onset of irrigation. Three-day-old fish larvae were released on day 10. Undigested organisms in the gut contents of the larvae or fry were identified on days 20, 26, 34, and 41, respectively. Ten-day-old larvae mainly preyed on Cladocera, but the fry thereafter shifted to Diptera as their main prey. While Cladocera and Podocopida decreased in fish-stocked plots, Euglenales and Halteriida became more abundant there. Top-down or bottom-up effects of fish seemed to control these changes in community structure.

W e compared the chlorophyll a concentration, taxonomic composition, and three-dimensional structure of periphyton communities developed in an artificial channel with and without deposits of biologically inert “s ilt” (silicon carbide particles). Algal community samples were collected 1, 3, 9-12 and 20-23 days after the start of the experiment, which was repeated six times. The presence or absence of “s ilt” deposits caused little differences in taxonomic composition or chlorophyll a concentration in pairwise comparisons, although significant differences in algal growth patterns were evident overtime. Chlorophyll a concentration, used as a proxy for algal biomass, often decreased between 9 -12 and 20-23 days provided no “silt” deposits were present, whereas it always increased continuously provided “s ilt” deposits were present. The latter pattern might be explained by the relatively closed biofilm structure that results from the inclusion of “ silt” particles since such a structure is probably more resistant to drag forces, and to being buoyed up by oxygen bubbles generated by algal photosynthesis, than a more open struchure without “ silt” accumulations.

湖底の光環境が1979年から2004年の琵琶湖南湖の沈水植物の分布範囲を制限する要因となっていたかどうかを検討した。滋賀県と国土交通省が行っている定期観測の透明度と水位のデータを用いて南湖に設定した200地点で沈水植物の分布の可否を推定した。全期間を通じて，沈水植物が分布可能な水域の面積は透明度でほとんど規定され，水位の影響は小さかった。観測された沈水植物の分布範囲の面積は，1979年から1994年までは潜在的な分布範囲の面積の9～48%に過ぎなかった。1994年9月におこった琵琶湖基準水位-1.23 mに達する極端な水位低下は，同じ時期に透明度が低下したために沈水植物の分布可能な範囲の拡大をもたらさなかった。また，1994年の8，9，10月の沈水植物の分布可能な範囲の面積は，1979～1993年のそれらに較べて特に広くなかった。以上の結果から，1979～1994年の南湖の沈水植物の分布範囲を制限していたのは湖底の光環境だけではないと考えられた。したがって近年の南湖の沈水植物の分布拡大は，光制限の存在を基盤とするカタストロフィックシフトでは説明できないという結論を得た。

How to define and construct a better relationship of coexistence between humans and nature through interactive museum activities is discussed based on the experiences of Lake Biwa Museum, Shiga, Japan. A better relationship cannot be determined objectively, and there is no justification for imposing one person’s subjective good on others. So the museum has avoided expressions that imply value judgments. Experience-learning programs and interaction using staff communicators in the exhibition rooms may have helped visitors to conceive the formation of a better relationship, but appear to have done little toward arriving at mutual agreement or understanding. Workshops may be an effective means of exploring conceptual agreement and understanding among various people. Although our exploration toward mutually intelligible concepts of a better relationship is still at a quite primitive stage, some concepts such as sustainability appear to have been accepted by most residents of Shiga Prefecture. Thus, the Restoration of Fish Breeding in Paddy Fields project is analyzed as a social innovation generated by collaborative and interactive activities in which the museum has engaged. The original idea behind this project was advanced by a researcher of the museum who learned much about local experiences from farmers around Lake Biwa. The cooperative response of the prefectural government and local communities to the museum’s suggestion appears to be based on rich social capital. Although the museum’s researchers contributed no more than the idea and some related knowledge, other actors such as farmers, prefectural agencies, and researchers in other research institutes organized and advanced the project. The museum is still engaged to the extent of studying the project’s effects or consequences, connecting researchers to the regions involved, and providing project-support participant events. We hope that further innovation along these lines will contribute to a “better relationship of coexistence between humans and lakes.”

The Identification System for Tanganyikan Cichlids (ISTC) is a computer system that identifies the species of Tanganyikan cichlids based on five meristic and three descriptive characters. An index I i is proposed as the degree of proximity between an unidentified specimen and species i. For calculating this index, the system allows the use of the following: (i) the range data including the largest and smallest values of meristic characters; and (ii) the meristics, between which the correlations are unknown. Therefore, a large amount of data accumulated in literature can be used. This system is sufficiently practical, although the methods are simplified and mathematically coarse.

We have developed a procedure to process echosounding data to map the distribution of submerged aquatic macrophytes in the southern basin of Lake Biwa, a water body that has a surface area of 52 km2 and a mean depth of 4 m. Echosounding observations were made along 27 transect lines spaced at 500-m intervals on August 4 and September 2 and 30, 2003. Quantitative vegetation data including percent coverage, mean vegetation height, and percent vegetation infestation were directly determined using image data from the echosounder recorded digitally on videotape. Based on the image data from an echosounder, a regression model was developed for estimating biomass of submerged macrophytes. The regression model using the total echo strength as the explanatory variable could reliably estimate macrophyte biomass up to 300 g m−2. Distribution maps of macrophyte height and biomass suggest that the recent summer decline of submerged macrophytes started earlier in shallow areas ( 4 m) in the southern basin of Lake Biwa.

Diatoms composing benthic microbial mats in Skarvsnes lakes, East Antarctica, were studied in terms of their taxonomy and relationship to environmental factors. Samples were collected from 13 freshwater lakes in the area. Amphora sp. (cf. veneta) was dominant in 11 of the 13 samples, while Craticula sp. (cf. molesta) and Diadesmis sp. (cf. perpusilla) were respectively dominant in the remaining 2 samples. Navicula ectoris Van de Vijver was also reported here for the first time in continental Antarctica. Mosses in the microbial mats did not have a significant effect on the diatom species composition. Redundancy analysis revealed that the main environmental gradient for diatoms was electric conductivity, despite its relatively narrow range (18-390 mS m^(-1)). Our results suggest that Diadesmis sp. and Psammothidium metakryophilum are halophobes, whereas Amphora sp. is a halophile.

We determined vertical changes in current velocity and dissolved oxygen concentration in biofilms on artificial and natural substrates using microelectrodes. We used biofilms developed on glass slides dipped in an artificial stream for 3 months, artificial clay tiles dipped in an outdoor artificial stream for 3 months, and natural pebbles. In the biofilm on a glass slide, current velocity significantly decreased from the surface of the biofilm and became 0 cm s−1 at the surface of the glass slide. Vertical profile of current velocity versus depth indicated a presence of a viscous sublayer of 0.2-mm thickness above the surface of glass slide. Dissolved oxygen (DO) concentration increased within the biofilm and attained the maximum (123%) at the surface of the glass slide, indicating active photosynthesis by sessile diatoms at the layer corresponding to the observed viscous sublayer. In the biofilm on an artificial tile, DO increased to 163% saturation at 24.849-mm depth, followed by rapid decrease (6%) at the surface of the tile. A similar result of remarkable decrease in DO saturation was also found in the biofilm on a natural pebble. These results suggest that smoothness of the substrate surface is related to the vertical profile of DO saturation. The thickness of the viscous sublayer and oxygen-depleted area (up to several hundred micrometers, μm) was sufficient for the presence of bacteria, protists, and other metazoan animals, suggesting high activity and diversity of those heterotrophs in the bottom part of biofilms.

琵琶湖南湖の52地点で, 2002年9月に潜水による沈水植物の定量採取を行った。沈水植物は43地点に出現した。平均現存量と出現地点数から, 調査時の南湖全体の沈水植物の現存量は10735±3030t, 分布面積は43km2と推定された。センニンモの現存量が最大で, これにクロモ, マツモ, オオカナダモ, ホザキノフサモを加えた5種で沈水植物全体の現存量の99%を占めた。センニンモとマツモの分布は高い重なり合いを示した (Pianka's α=0.71)。沈水植物の現存量と環境要因についてSpearmanの順位相関係数を求めた。センニンモの現存量は平均透明度/水深比との相関が最も強く (ρ=0.50), 湖底の相対的な光の強さが現存量の大きさを規定する可能性が示された。マツモの現存量は透明度と正の相関を (ρ=0.44), オオカナダモの現存量は底質の平均粒径 (φmean) と負の相関を示した (ρ=-0.40)。南湖の沈水植物の現存量の歴史的変遷を整理した。2002年の沈水植物の量的な種組成は, かつて沈水植物が豊富だった1936年と大きく異なっていた。

The horizontal distribution of dissolved oxygen (DO) concentrations on the lake bottom was investigated on September 2-5, 2002. At 36 out of the 84 sites, DO concentrations were at less than 50% of saturation. The biomass of macrophytes was investigated on September 6- 11 at 44 sites, and ignition loss of sediments was investigated at 41 sites on September 17-18. The results of multiple regression analysis suggested that DO concentrations could be estimated using the biomass of Egeria densa, Myriophyllum spicatum, and Potamogeton maackianus, and the water depth as explanatory variables (R = 0.65, R' = O.61, n = 44, P 0.01). Both the partial correlation coefficient and partial regression coefficient indicated that biomass of Egeria densa was the most influential environmental factor on the fluctuation of DO concentrations on the bottom water.

琵琶湖南湖の沈水植物の分布と現存量を,魚群探知機を用いて推定した。GPSの位置情報と対応した魚群探知機像に基づいて,沈水植物群落の分布を地図上に示した。また,魚群探知機の像と潜水調査で得られた現存量との対応関係をモデル化し,これを南湖全域から得られた魚群探知機像に当てはめて,群落の面積および現存量を算出した。沈水植物群落の面積は32km2(南湖全域の58%),現存量は乾重量で7.1×104tと推定された。この面積と現存量はともに,1960年代に沈水植物の減少が明らかになるよりも前の記録と同程度かそれ以上である。地図上に示された沈水植物の分布と,透明度から予測される分布可能域を比較検討した。1994年には,光条件の上で生育可能と考えられる場所の多くに群落が分布していなかった。一方,2001年における沈水植物の分布は,透明度から算出された補償深度によりほぼ説明できた。1994年以降の沈水植物の増加は,光条件の上で生育可能な場所に,沈水植物が徐々に侵入・定着することによって起こったと考えられた。

滋賀県水産試験場が73年にわたって観測した透明度のうち,沖合い3地点(St.II-IV)のデータについて長期的な変遷を統計的手法を用いて解析した。透明度の年平均値についてスプライン関数による最適モデルを求めたところ,St.II,IIIでは低下→横這い→低下→上昇の4区間モデルが最適となった。St.IVでは低下→上昇→低下→横這い→上昇の5区間モデルが最適だったが,St.II,IIIと同様の4区間モデルも2番目に適していた。4区間モデルの場合,区間の境目は3地点でよく一致し1950年付近,1975年付近,1990年付近となった。別の解析方法として1949年以降のデータについて60カ月移動平均を求めたところ,年平均値のスプライン関数モデルと同様の解釈をする事ができた。透明度の経月変化パターンを10年区切りの平均で比較した。1920-50年代には6-8月の透明度のピークの消失が,1980年代・90年代には5月の透明度の著しい低下が特徴として検出された。1990年代の透明度の上昇期には,植物プランクトンの現存量が増加していることから,植物プランクトンのサイズ組成の変化が透明度を規定する重要な要因である可能性が示唆された。

1998年3月から2000年11月にかけて,琵琶湖南湖周辺の10市町村の琵琶湖岸,内湖,河川,水路,池など879地点を調査し,16科42属55種(亜種を含む)の魚類を採集した。オイカワ,カワムツA型,カワムツB型,タモロコ,カマツカ,ギンブナ,アユ,トウヨシノボリなどの在来種は多くの調査地点に分布していた。一方,外来種のブルーギルやオオクチバスも多くの調査地点で採集された。分布パターンを魚種で分類するためにクラスター分析を行った結果,AからDの4つのクラスターが不明瞭ながら認められ,分布パターンと地形との間に関係が認められた。オイカワやカマツカに代表されるクラスターAとタイリクバラタナゴやメダカに代表されるクラスターBの多くは,デルタ帯,扇状地帯に広く分布するが,カワムツA型やタモロコに代表されるクラスターBの一部はデルタ帯に分布しない。その一方で,カワムツB型に代表されるクラスターCは丘陵地に分布し,ブルーギル(クラスターD)はデルタ帯に分布していた。タモロコやカワムツA型などクラスターBの一部の魚種はブルーギルの影響を強く受けているものと思われた。

京都市の賀茂川中流域の一形態単位内で,珪藻群落の生息場所による違いを調べた。試料は大礫の上面,中礫,砂,ツルヨシPhragmites japonicaの匍匐茎から毎月2回ずつ,1年にわたって採集した。各生息場所ともに,付着藻類の季節的な現存量変動は大きく,特に大礫上では変動が大きかった。中礫上の現存量は,砂上,ツルヨシ上に比べて有意に小さかった。ほとんどの場合,珪藻群落の生息場所間での種組成の違いは,同一生息場所内で同時に採集された2本の群落試料間の種組成の違いよりも大きかった。従って,珪藻群落の種組成は生息場所間で異なっていたと結論できる。大礫・砂・ツルヨシ上の珪藻群落の種組成は,互いに大きく異なっていたが,中礫上の種組成は他のいずれとも共通性があった。砂上ではNauicula spp.など,運動性の高い珪藻が多かった。ツルヨシ上では夏期から秋期にかけてCocconeis placentulaが著しく優占した。大礫上でHomoeothrix janthinaなど叢生糸状ラン藻が著しく優占した際には,Achnanthidium japonicumやNitzschia hantzschianaが珪藻の中での優占種になることが多かった。

Since the turn of the twenty-first century, two means of promoting the use of rice paddies as fish nursery ground have been implemented around Lake Biwa in Japan. One involves fish culture: newly hatched or pre-flexion larvae are released into rice paddies after the rice transplantation, and then reared to juveniles before the mid-season drainage. The other involves the installation of fish passes to enhance the entry of adult fish into paddies and encourage their natural reproduction there. These efforts mainly aim to enhance the reproduction of round crucian carp (nigorobuna), Carassius auratus grandoculis, an endangered endemic subspecies inhabiting Lake Biwa, which is also the principal ingredient in funa-zushi, a specialty food of Shiga Prefecture. Both methods are regarded as environment-friendly and thus are well supported by local people. Our studies on the rice paddy food chain revealed, however, that the impact of round crucian carp larvae/juveniles on aquatic biota in rice paddies is profound. Fish predation results in an extreme reduction of Cladocera, and a concomitant increase in the food species and competitors of cladocerans. Through their benthic foraging, juvenile fish also cause a rise in total phosphorus concentration and phytoplankton in the paddy water. In addition, scarce competitors and predators in the paddies contribute to the rapid growth and low mortality of the fish larvae/juveniles. Although the employment of rice paddies as fish nursery ground may be effective for the conservation of round crucian carp, other approaches are also needed to enhance the overall biodiversity of rice paddy areas around Lake Biwa.

School of Earth and Environmental Science (Oceanography), Seoul National University, Seoul 151-742, Korea; (present address: University of Rostock, Institute of Biological Sciences, 18051 Rostock, Germany); jinsoonpark@snu.ac.kr Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan. ohtsuka@lbm.go.jp School of Earth and Environmental Science (Oceanography), Seoul National University, Seoul 151-742, Korea. kohch@snu.ac.kr

The Japanese Journal of Limnology is another official publication of the Japanese Society of Limnology. The original papers in the journal were peer-reviewed by a few authorized referees, and appeared in Japanese with English abstracts.