DAIpo (Diatom Assemblage Index to organic water pollution) is a biological index calculated from the species compositional data of a diatom assemblage. DAIpo itself is a simple index, but it is based on the original classification system of diatom taxa. First, diatom samples collected at more than 1000 stations in Japanese freshwaters were analyzed by the original ordination technique to obtain an order of diatom taxa, of which the endpoints were forced to be Nitzschia palea and Achnanthes japonica. Then, the taxa were classified into three groups according to the obtained order. It is assumed that this classification reflects the pollution tolerance of each taxon because water pollution is regarded as the most important environmental gradient in Japanese freshwaters.
In the present paper I point out that there are problems to be solved or explained in this ordination procedure.
1) Why do the endpoints need to be Nitzschia palea and Achnanthes japonica
2) Why should the endpoints of the taxon ordination be determined? If water pollution is truly the most important environmental gradient, usual ordination techniques such as corresponding analysis can extract the first axis representing water pollution.
3) Were there other community gradients in the data set used to construct the classification system of diatom taxa for DAIpo? Such gradients might disturb the community gradient corresponding to the water pollution gradient. If this happened, the classification of diatom taxa used in DAIpo could also be disturbed by these other gradients.
The relationship between DAIpo and other biological indices is still unclear. The relationship between DAIpo and Shannon's diversity index has been discussed in a few previous papers, though it should be noted that some of the structure observed in the relationship is caused by the formulae of DAIpo itself.

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DAIpo (Diatom Assemblage Index to organic water pollution) indicates the approximate position on the coenocline of Japanese freshwater periphytic diatoms, because it is based on an ordination technique for extensive data of such diatom assemblages. As it is established without employing environmental parameters, the environmental conditions which it indicates are unclear and disputable despite being regarded as an index of saprobity. It is very difficult to estimate saprobity in situ because it relates to the strength of organic matter decomposition. It cannot be fully represented, moreover, by a single environmental parameter such as BOD or dissolved oxygen. Since saprobity is related to multiple environmental factors, multiple regression analysis or related statistical methods are theoretically effective to elucidate what DAIpo indicates, if it indeed indicates saprobity. Such analyses hitherto showed that DAIpo could not be reduced to any single environmental parameter which is usually measured. It was also suggested that phosphorus concentration and oxygenic condition affected DAIpo. Although these analyses usually displayed strong effect of electric conductivity on DAIpo, it is probably false effect due to the measurement error of the other environmental parameters. Usually DAIpo is lower in summer than in winter. It suggests the nature of the saprobic index, because higher temperature causes faster organic matter decomposition and low capacity of dissolved oxygen, and as a result, it becomes more hypoxic under dark conditions. Confirming what DAIpo indicates, therefore, needs further studies concerning environmental parameters which are apparently related to saprobity but have been ignored, such as daily minimum dissolved oxygen. Because Achnanthes japonica and Nitzschia palea were fixed as endpoints for the ordination to classify diatom species into three groups, DAIpo is also possibly affected by their ecological characters rather than just the reaction to organic pollution.

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The recent fast development of diatom taxonomy has caused confusion in the applied research on biological indicators. Here I discuss the history of diatom taxonomy and several topics related to biological indicators : SEM observation, new genera, cryptic species, endemic species, and molecular approach. The use of species complexes helps to avoid the confusion of taxonomy in applied research. The way to harmonize new taxonomy and applied research is also discussed.

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We investigated the recent diatom assemblages in 30 surface sediment samples from Osaka Bay, Japan, with the identified diatoms divided into five categories [halobious system ; Oligoeuryhaline Polyhalobous (OPH), Euryhaline Polyhalobous (EPH), Mesohalobous (MEH), Euryhaline Oligohalobous (EOH) and Stenohaline Oligohalobous (SOH)] based on their tolerance for salinity. The horizontal distribution pattern of each category suggested that the recent diatom distribution pattern of the bay is mainly controlled by the transportation of brackish/freshwater species from the mouth of the Yodo River through the river-water discharge into the bay. In other words, the distance from the river mouth controls the relative abundance of brackish/freshwater species at each site, which is a major part of the total floral composition and could be a useful paleoecological indicator for river-water discharge. The distribution pattern of Chaetoceros resting spores suggests they have potential as a paleoecological indicator for anthropogenic environmental degradation in exploited embayments. Taphonomic processes of recent diatoms are also discussed.

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ブラジル産Melosira undulata (Ehrenb.) Kütz. var. normanii Arn．に関する初めての報告である．Guaíba川の砂試料とLagoa Emboaba（Rio Grande do Sul State, Brazil）のプランクトン試料に基づき，微細構造を観察した．本種は殻套の中央部にある唇状突起から粘質の柄を出して砂粒に付着する．肋に区切られた殻表面の小室の構造を詳しく記述した．本種の微細構造をMelosira C.Agardh，Ellerbeckia R.M. Crawford，Orthoseira Thwaitesおよびヒアロディスクス科の各属と微細構造を比較したところ，Melosira のそれとよく一致した．

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本州北部，秋田県仙北市に分布する中新−鮮新世の堆積物である宮田層から見出された新種Stephanodiscus uemurae sp. nov．を記載した．本新種の以下に述べる特徴を，光学顕微鏡及び走査電子顕微鏡写真で示した．殻面が2重の同心円状に弱く波打ち，束線は殻の中心では1列であるが殻面／殻套境界では2列〜3列になる．針はすべての殻面／殻套境界の間束線上にあるが，殻套有基突起の開口がある間束線上には存在しない．殻套有基突起の開口は普通，間束線の2—3本ごとにあるが，針の位置にある場合もある．唇状突起は1個で，外管は殻面／殻套境界で1本の針と置き換わって，針の列よりやや殻面寄りに所在する．内面では殻面の胞紋列と殻套の胞紋列間にしばしば僅かな無紋域がある．普通，殻面には有基突起が存在しない．

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A study was conducted on the diatom flora and its distribution along the Sendai River, which flows into the Japan Sea in Tottori Prefecture in western Honshu, Japan. Diatoms were collected from cobbles near the riverside at each of 26 sampling sites in July-August 2006. A total of 165 diatom species belonging to 55 genera were identified and illustrated together with 10 unidentified ones. The predominant genera were Navicula and Nitzschia, represented by 21 and 17 species and by relative frequencies of 17% and 21%, respectively. The DAIpo value for each site was between 64 and 89, indicating that all sites were oligosaprobic. Distribution of Gomphonema parvulum inclined toward the upper part of the Sendai River, as found in some other rivers flowing into the Japan Sea in western Honshu.

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長野県木曽川支流の小川にてアジメドジョウ（Niwaella delicata）の採食に対する付着藻類の抵抗性を調査した．抵抗性の違いを評価するため，アジメドジョウの消化管内容物および食物である付着藻類群落中に含まれる藻類の相対比率を用いてChessonの選択指数を算出した．その結果，選択指数の値は藻類種類間で異なり，7種の珪藻優占種の選択指数はその細胞サイズと共に大きくなった．アジメドジョウの採食に対する抵抗性は藻類種類間で異なり，匍匐型糸状藍藻および大型珪藻（Ulnaria ulna）は採食されやすかったのに対し，直立型糸状藍藻および小型珪藻（Achnanthidium convergens，Fragilaria perminuta，Gomphonema parvulum，Cymbella turgidula var. nipponica およびEncyonema sp.）は採食されにくかった．

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An attached diatom, Arachnoidiscus ornatus Ehrenb., has been known as a fouling organism on the commercially important agarophyte, Gelidium elegans Kütz. in Japan. When Gelidium thalli heavily covered with A. ornatus were dried before shipment, they turned grayish green from red (original thallus color) because of the discoloration of A. ornatus, resulting in the reduction of their commercial value. In this study, the occurrence of A. ornatus on G. elegans was monitored seasonally and quantitatively by collecting G. elegans at three sites along the coast of Himi City, Toyama Bay from 2004 to 2006. Coverage of A. ornatus on G. elegans was measured using the scanned photographs (600 dpi) of G. elegans thalli. In 2004 and 2005, higher coverage appeared from summer to autumn (up to 20 to 40%), namely the harvest season of G. elegans, while coverage was lower in the winter and spring. In 2006, as our previous studies showed that common gastropods in the Gelidium beds never affected the abundance of A. ornatus, effects of water temperature and nutrients were examined by culturing the fouled Gelidium branches in surface seawater, deep (i.e., nutrient-rich) seawater (DSW) and three levels (25, 50 and 75% DSW) of mixed seawaters at 10, 20 and 30°C. The number of attached A. ornatus increased in 50 to 100% DSW at 10 and in 25 to 100% at 20°C but decreased in every culture medium at 30°C. These results show that the abundance of A. ornatus is highly dependent on nutrient levels and the temperature of the Himi coastal waters (ca. 10--27°C).

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鹿児島県に分布する郡山層の珪藻土からPliocaenicus omarensis (Kupts.) Stachura-S. & Khur．と同定で きる分類群が見出された．郡山層から見出された本種の特徴は以下の通りであった．殻面は横に波打ち，殻面の点紋は放射状〜不規則で，殻面有基突起はほぼ円形に分布していた．殻面・殻套の有基突起は3個の付随孔を持ち，殻套有基突起は僅かに窪んだ肋に所在していた．ligula-like segmentは接殻帯片の開口部 を覆っていた．

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琵琶湖の北約5kmにあるミズゴケ湿原，山門湿原の珪藻植生を調べた．2006年5月および11月に，計46試料を採集して精査したところ，36属123種の珪藻を同定することができたので，未同定の7種とともに写真入りチェックリストとしてまとめた．最も多くの種を含んでいた属はEunotia およびPinnularia で，各19種を占めた．しかしその珪藻全種に占める割合（E＋P）は29％と，これまでに日本のミズゴケ湿原から報告されている値に比べて低かった．同じ琵琶湖集水域に位置する八雲ヶ原湿原から報告された51種のうち，41種までが山門湿原でも見出された．山門湿原は暖温帯上部に位置するにもかかわらず，Eunotia nipponica Skvortsovなど寒地性と考えられる珪藻がいくつか出現した．この結果は，この湿原の維管束植物や昆虫にも寒地性のものが多いこととよく対応している．

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別寒辺牛湿原は北海道東部，厚岸町にある低湿地で，広い低層湿原域と孤立した高層湿原域からなる．2008年11月と2009年5月に高層湿原域から計5試料を採集し，4属7種の珪藻を見出した．2008年11月に採集した試料ではPinnularia subcapitata var. elongata が優占種だったのに対し，2009年5月に採集した試料ではEunotia bilunaris var. bilunaris が優占種となった．

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We investigated an epilithic diatom assemblage collected at a downstream site of the Takao River, Fukuoka Prefecture, on November 12, 2008. The sample was examined with a light microscope and a scanning electron microscope. Each taxon was photographed and measured for identification. Twenty-two taxa belonging to 11 genera were recorded. Cymbella leptoceros, Achnanthes subhudsonis, and Navicula minima were abundant. The DAIpo value was 83.8, indicating β-oligosaprobic level.

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Diatom assemblages were studied in three strongly acidic hot springs in Akita Prefecture, northern part of Japan. Eunotia exigua and Pinnularia acidojaponica were recorded in the three springs, Fukenoyu, Tamagawa and Kawarage, with P. acidojaponica dominant in all the springs. Relative abundance of E. exigua was slightly increased in Fukenoyu, which has the highest water temperature and the lowest pH of all the springs.

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Diatom assemblages were studied from the Toyokawa River, which is located in the central part of Akita Prefecture, northern part of Japan. A total of 78 taxa among 44 genera were recorded. The following 12 taxa were observed from all five stations: Melosira varians, Fragilaria capitellata, Fragilaria vaucheriae, Meridion circulare var. constrictum, Gomphoneis okunoi, Planothidium lanceolatum, Navicula gregaria, Navicula lanceolata, Nitzschia dissipata var. media, Nitzschia inconspicua, Nitzschia tubicola, Surirella angusta. Diatoma tenuis var. moniliformis was recorded in Japan for the first time.

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フィリピン最大の湖，バイ湖（Laguna de Bay：ラグナ湖）の珪藻の写真入りチェックリストを作成するとともに，出現した珪藻と水質との関係を検討した．1976年と1997年に採集したサンプルから，37属83種の珪藻を同定し，未同定の15種とともに写真を示した．未同定種を含めた属ごとの出現種数はGomphonemaが12種で最も多く，NitzschiaおよびNaviculaの10種がこれに続いた．バイ湖の塩分は淡水湖の範疇にあった（＜0．4‰）にもかかわらず，海産とされるGiffenia cocconeiformisが出現した．また，有機物および栄養塩がたいへん豊富だったにもかかわらす，好汚濁性の種は比較的少なく，一方で好清水性の種も出現した．

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The organic pollution of Arakawa River in Kofu city was assessed using the diatom assemblage index to organic pollution (DAIpo). The DAIpo values were 98, 45 and 45 at the up-, mid- and downstreams, respectively. BOD at the mid- and downstreams were threefold higher than at the upstream. Among the dominant diatoms at the upstream, Encyonema silesiacum and Hannaea arcus var. hattoriana, were also abundant in 1977, suggesting little change of the diatom species composition during 30 years despite the dam construction.

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Three diatom indices, Diatom Assemblage Index to organic water pollution (DAIpo), the water quality evaluation of Japanese-type River (WQEJR), and the trophic diatom index (TDI), were calculated based on epipelic diatom assemblages to test their applicability. The dominant diatom taxon was Navicula gregaria at three out of the five sampling sites. At the other two sites, Nitzschia inconspicua and Nitzschia dissipata var. media were the dominant species, respectively. Based on epipelic diatoms, the three diatom indices showed almost the same correspondences to the water quality as those based on epilithic diatoms. Correlations between the indices and the water quality were, however, not as expected from the nature of the indices. For instance, higher values of TDI at sites with low phosphorus concentrations were associated with the dominance of N. gregaria, which usually indicates high phosphorus concentrations on stones.

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The diatom flora in the moat around Takashima Castle, Suwa City, Nagano Prefecture, was studied in January 2009. A total of 48 diatom species belonging to 26 genera were identified. The predominant genera were Navicula and Nitzschia represented by six and five species, respectively. Aulacoseira ambigua (Grunow) Simonsen was dominant. Rhopalodia gibba var. ventricosa (Kütz.) H.Perag. & Perag., Epithemia sorex Kütz. and Cyclostephanos dubius (Fricke) Round were also abundant.

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