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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This is the first study of the freshwater diatom Melosira undulata (Ehrenb.) Kütz. var. normanii Arn. from Brazilian waters. The fine structure was studied based on sand samples from Guaíba River and plankton from Lagoa Emboaba (Rio Grande do Sul State, Brazil). The diatom attaches itself to sand grains by secreting mucilage stalks from its sessile rimoportulae, which are located in the middle of the mantle. The loculate wall structure is described in detail and the fine structure is compared to species of Melosira C.Agardh, Ellerbeckia R.M.Crawford, Orthoseira Thwaites and genera of Hyalodiscaceae. The features observed are in agreement with Melosira

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A recently found Stephanodiscus fossil, S. uemurae sp. nov., from Mio-Pliocene sediment of the Miyata Formation, Senboku City, Akita Prefecture, northern Honshu, Japan is described here. The new species is characterized by having a slightly double concentric undulation of the valve face, uniseriate fascicles at the valve center and biseriate or triseriate fascicles at the valve face/mantle junction. There is often a slight break between the rows of areolae on the valve face and mantle. Usually, there are no valve face fultoportulae. Spines are located on all interfascicles at valve face/mantle junction except in the case where openings of mantle fultoportulae are present, which is usually every two or three interfascicles. One tubular rimoportula replaces a spine and is located slightly above the ring of spines. The new species is illustrated with LM and SEM photographs.

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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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Algal vulnerability to the grazing loach, Niwaella delicata, was investigated in the Ogawa stream, a tributary of the Kiso River flowing through Nagano Prefecture, Japan. To evaluate the vulnerability, Chesson's electivity index was calculated using the relative abundance of ten dominant algal taxa in the gut contents of the loach and benthic algal assemblage. The index values differed significantly among the algal taxa and the index values of diatoms increased with their size. The results showed that vulnerability to the loach differed among algal taxa. Prostrate filamentous cyanobacteria and the large diatom, Ulnaria ulna, were susceptible to loach grazing, while upright filamentous cyanobacteria and small diatoms such as Achnanthidium convergens, Fragilaria perminuta, Gomphonema parvulum, Cymbella turgidula var. nipponica and Encyonema sp. were less susceptible to loach grazing.

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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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Pliocaenicus omarensis (Kupts.) Stachura-S. & Khur. was found in diatomite from the Koriyama Formation, Kagoshima Prefecture, Japan. It is characterized by a transversely undulate valve face, puncta that are radially to randomly arranged on the valve face, valve face fultoportulae with three satellite pores arranged in a circle, mantle fultoportulae also with three satellite pores located on slightly recessed costae and a ligula-like segment covering the valvocopula opening.

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A taxonomic survey was carried out on the diatom flora of Yamakado Moor, a mixed Sphagnum moor located about 5 km north of Lake Biwa in west-central Honshu, Japan. In total, 123 diatom species belonging to 36 genera were identified and are illustrated here with seven unidentified species. The predominant genera were Eunotia and Pinnularia, each represented by 19 taxa, but their proportions are lower than in the high-moors of Honshu. Forty-one out of 51 taxa reported earlier from Yakumogahara Moor, another Sphagnum moor located in the watershed of Lake Biwa, were also observed in Yamakado Moor, although the taxa richness is much higher at the latter site. Similarly to the vascular plant flora and insect fauna, the diatom flora contained boreal or alpine components despite the moor's location in the warm-temperate zone.

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Bekanbeushi Wetland is located in Eastern Hokkaido, Japan. It consists of a large low-moor and isolated high-moors and preserves natural flora of acid low-moor. We collected diatoms from a wetland high-moor in November 2008 and May 2009. A total of 7 diatom species belonging to 4 genera were identified. Dominant species were Pinnularia subcapitata var. elongata in the November 2008 samples and Eunotia bilunaris var. bilunaris in the May 2009 samples.

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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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A taxonomic survey of the diatom flora of Laguna de Bay, the largest lake in the Philippines, was conducted with special reference to the slightly brackish and heavily polluted water quality. Based on samples collected in 1976 and 1997, we identified 83 diatom taxa belonging to 37 genera. They are illustrated here together with 15 unidentified taxa. The predominant genus in term of species richness was Gomphonema, represented by 12 species. Nitzschia and Navicula were subdominant each represented by 10 species. A euhalobic species, Giffenia cocconeiformis, occurred despite the low salinity (<0.4‰). Regardless of the heavy organic content and high phosphorus concentration of the lakewater, saprophilous species were not common, and some saproxenous species occurred.

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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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