The diatom assemblage in an alkaline hot spring which is the most alkaline spring in Japan with 10.1 in pH value was investigated. A total of 20 taxa belonging to 9 genera were recorded. Am ong them, we paid an attention to the occurrence of unexpected two taxa e. g. Tabellaria flocculosa and Achnanthes minutissima var. minutissima. The former has been regarded as an acidophilous taxon by many investigators and the latter has occurred abundantly not also in various water environments with pH value above 5, but also in waters affected by the mining effluent. We would like to call such the taxon as above mentioned and the community which occurred near the ends of environmental gradient as “environmental frontier species” and “environmental frontier community” respectively.
Pinnularia acoricola Hustedt was found in Java by F. Hustedt (1934). After that, this taxon has been widely recorded from Africa by some researchers. In our research, this taxon occurred abundantly in 33 sites having extremely acid water environment with 1.1-3.9 in pH value. Especially in 9 sites of which pH values were below 2.0, rela tive abundance of this taxon in each diatom assemblage reached over 90 percent. From above mentioned facts, it seems to suggest that this taxo n has a special characteristic being able to extremely increase and form a community balanced with extremely severe environment. The authors wish to propose to call “environmental frontier species” and “environmental frontier community” for such the species and community survived on near the ends of environmental gradient.
Tolerance indices to organic water pollution of 709 epilithic diatom species which were obtained from 1240 attached diatom assemblages were calculated by using two typical species. Nitzschia palea and Achnanthes japonica were selected as tolerant and intolerant typical species to organic water pollution, respectively. These two species were used for setting a hypothetical axis of organic water pollution in numerical calculation of tolerance indices of each diatom species. Coexistence indices of epilithic diatom species pair also were calculated statistically. Two distinct boundaries were successfully recognized within the order of tolerance indices by comparing and examining the coexistence indices. Therefore, epilithic diatom species were classified objectively and nationally into three ecological groups (saprophilous, indifferent and saproxenous species) by setting up two boundaries. Both saprophilous and saproxenous species were decided now and were increased in number than previous report (Watanabe et al.1990). Based on the objective and statistic classification executed in this study, DAIpo (Diatom Assemblage Index to organic water pollution), whose value was numerically estimated by using relative abundance of each ecological group, is considered to became more reliable for water quality assessment.
Species components of 1240 epilithic diatom assemblages were used for statistical studies on organic water pollution. The coexistence index of each pair of epilithic diatom species based on the order of tolerance index to organic water pollution was examined and compared (Asai 1995). As a result of the study,709 epilithic diatom species were classified into three ecological groups (saprophilous species, indifferent species and saproxenous species) by the new method which was more reasonable from ecological viewpoint comparing with the old method (Watanabe et at.1986). In this paper, we show all taxa with synonyms belonging to saprophilous and saproxenous species groups. The number of species belonging to the two groups increased and their ecological groups in some species changed. Almost all diatom taxa belonging to the two groups were cosmopolitans in the world. The diatom assemblage index to organic water pollution (DAIpo) can also be estimated more reasonably by using relative abundances of both saprophilous and saproxenous taxa which were listed in this paper, in each sample.
Diatom populations from the Rivers Pergau, Renyok, Ayer Lanas, Lata Rek and Jeram Lenang, Kelantan, Malaysia were investigated from 3rd-5th May,1993. The 39 taxa from 13 genera were recorded. Fragilaria vaucheriae,Fragilaria pinnata var. intercedens and Cymbella tumida were major diatoms in the rivers. The following three taxa are new record for Malaysia: Navicula muncki, Navicula terminata and Neidium gracile.
SEM observations are reported on a naviculoid raphe-system intricate with several accessory components: shark fin-like vanes here termed dorsicentral and subcaudal fins, dorsal ridges of keel, a longitudinal groove. between the ridges and helictosiphons at poles in addition to the ordinary raphe on highly vaulted valves. Four new species are described under Dichotropiscus, a new genus, characterized by sharing this system. They are D. fimbriatus, D. bicostatus, D. brevilanceolatus and D. staurophorus. Morphological details and functional accounts are given in relation to the fins.
The pennate diatom Nitzschia multistriata Takano 1993 has so far been found in eutrophic bays of southern Japan during warm seasons. As this diatom is not carrying its central nodule on the pseudoraphe, it is clearly different from many other Nitzschia species which are customary carrying its central nodule. Therefore, some researchers are recently going to establish a new group as the new Genus ‘Pseudo-nitzschia’. With this change of the generic name, the new name Pseudo nitzschia multistriata (Takano) Takano is proposed for its further utilization. The hyphen which is placed between ‘Pseudo’ and ‘nitzschia’ is absolutely necessary, because The name of a genus may not consist of two words, unless these are joined by a hyphen (ICBN, Tokyo Code,20.3. ).
The Onogami Formation, an early Pleistocene lacustrine deposit, is located 120 km northwest of Tokyo. Samples were collected from the type locality of the Onogami Formation. The diatom assemblages are composed of 26 species belonging to 18 genera. The diatoms of this formation are characterized by Cyclotella radiosa (Grun. ) Lemm., C. reczickiae Churs. et Log., Stephanodiscus alpinus Hust., S. sp., Aulacoseira ambigua (Grun. ) Sim., Ellerbeckia arenaria (Ralfs) Crawford var. teres (Brun. ) Crawford.