Unplanned anthropogenic activities have contributed to the shrinkage of wetlands as well as degrading their quality. This necessitates watershed-based planning such as inventorying, mapping and regular monitoring with cost-effective and reliable assessment protocols. Diatoms have been used across continents as bioindicators for reflecting the physical, chemical and biological integrity of their habitats. The current study attempts to understand the role of environmental factors in the formation of the diatom community structure in the shallow wetlands of Peninsular India. Diatoms from different habitats and water chemical variables were assessed for 43 wetlands of Bangalore, a profoundly urbanized region of Peninsular India. A total of 181 diatom taxa from 45 genera highlights the rich biodiversity of the region. Wetlands located in the densely populated urban regions are dominated by a prolific growth of eutrophic indicator species such as Gomphonema parvulum Kütz., Nitzschia palea (Kütz.) W.Sm., N. umbonata (Ehrenb.) Lange-Bert., Diadesmis confervacea Kütz., Cyclotella meneghiniana Kütz. and C. atomus Hust. Wetlands located at the outskirts of the city characterize oligo-mesotrophic conditions where Achnanthidium sp. dominates. Detrended canonical correspondence analysis showed a strong influence of eutrophication and organic/inorganic pollution on diatom assemblages but a relatively weak influence of conductivity. TWINSPAN shows grouping of wetlands based on species composition and suggests that Achnanthidium sp. and Cyclotella meneghiniana are initial indicator taxa for oligo-mesotrophic and eutrophic conditions respectively. These results indicate that the environmental factors consistently act as limiting variables in structuring diatom assemblages at a regional scale in urban ecosystems. The study provided insights into the ecological importance of endemic diatoms found in different environments. Thus, diatom-based biomonitoring can become a viable surrogate for physical and chemical parameters of water quality. Also, region-specific diatom indices will enable the easy and efficient investigations of wetlands.
A new fossil centric diatom species Dimidialimbus bungoensis belonging to a new genus Dimidialimbus is described based on an Early Pleistocene sediment sample from the Omoto Formation located in Oita Prefecture, Kyushu, Southwestern Japan. The most similar species by LM comparison is Cymatotheca weissflogii (Grunow) Hendey. The new species, however, lacks a mantle on the concave side of the valve and has mantle fultoportulae located on costae as well as a flat hyaline zone forming a broad rim on the concave side that lacks mantle fultoportulae. These characteristics do not fit the genus Cymatotheca Hendey nor Thalassiosira Cleve, Pliocaenicus Round & Håkansson or any of the other established genera of Thalassiosirales Glezer & Makarova.
A new diatom species Extubocellulus brasiliensis M.Garcia belonging to the family Cymatosiraceae is described from Brazilian beaches of South Atlantic Ocean. Extubocellulus brasiliensis M.Garcia was found in marine sandy beaches forming a short colony (4 cells). It is characterized by the presence of a one row of round areolae occluded by an external cribrum between the valve face and the mantle, and an ocellulus located symmetrically at each apex composed of 4 porelli.
We studied the diatom flora of the Koyama-ike pond located in Tottori Prefecture in western Honshu, Japan. The pond is a closed lagoon facing the Japan Sea. Diatoms were collected monthly from a cedar board set at four stations near the pond shore from February 2010 to January 2011. The water was fresh to slightly brackish during the sampling period. A total of 225 diatom species belonging to 67 genera were found. These were all illustrated and identified except 18 unidentified ones. The predominant genera were Navicula, Nitzschia and Gomphonema represented by 27, 24 and 18 species, respectively. Our diatom flora is sometimes different to those of past studies in the 1960s, even though the pond salinity was mostly the same as during our sampling period. This difference may be partly attributed to the eutrophication.
Diatom assemblages in a rice paddy inundated by the 2011 Tohoku Earthquake tsunami were studied. We collected diatom samples from a rice paddy in Sabusawa Island in Miyagi Prefecture on 14 August 2011. The rice paddy was intruded by seawater during the high tide of the spring tide as a result of destruction of the coastal levee and the land subsidence after the earthquake. The salinity of the paddy was slightly higher than that of the coastal seawater, and naturally, rice was not cultivated at that time. In total 117 diatom taxa （including 22 unidentified ones） belonging to 50 genera were observed. The diatom assemblages consisted of fresh, brackish, and marine water species, and moreover, extinct Miocene marine diatoms. The dominant species was Tabularia parva on Zannichellia palustris and in a floating algal floc, and Navicula phylleptsoma on the surface soil. Halamphora luciae was subdominant in all samples. Judging from the past literature, these diatoms all tolerate changes in salinity.
We studied epilithic diatom assemblages and their association with the environments of the Ai River, a subsidiary stream of the Yodo River, in west central Japan. Diatom samples were collected in August and December, 2009. Melosira varians that tends to be grazed by aquatic animals was usually dominant, especially in the lower parts of the river. In the upper parts of the river, sessile diatoms such as Achnanthidium minutissimum and Planothidium lanceolatum were abundant in summer, while Diatoma vulgaris and Nitzschia dissipata were abundant in winter. Rhoicosphenia abbreviata which firmly adheres to the substrata by a short stalk was dominant at the site with the highest stream gradient. Luticola ventriconfusa was dominant in the lowest part of the river, suggesting tidal influences. DAIpo （Diatom Assemblage Index to water pollution） was higher in the upstream to midstream parts than in the headwater. This pattern significantly corresponded to the river gradient.