Oligotrophy: the forgotten end of an ecological spectrum

Most studies that consider the relationship of diatoms and water quality have focused their attention on the questions and practicalities of water pollution or perturbations in some form or another. Many models and studies have demonstrated the environmental tolerances or changes in structure of diatom communities related to environmental challenges. This focus on the impacted end of the water quality spectrum has led, of necessity, to issues ultimately related to habitat restoration. We contend that a concentrated effort to develop more fully the theory and there is a need for practice related to oligotrophy, the other, ignored end of the water quality spectrum. We explore the historical usages of the term oligotrophy, as well as the challenges and promise of autecological and community approaches to understanding oligotrophy, and the possibility of focusing more on conservation rather than restoration in water quality issues

Taxonomy and distribution of diatoms on the Turkish Mediterranean Coast, Dalyan (Muğla)

Diatoms are one of the components in the littoral zone and the most productive in terms of O2 production and primary production. Despite their importance in these coastal ecosystems, the diatoms of littoral zones of Turkish coastlines have been understudied.  In this report, we document the littoral diatoms from Dalyan Iztuzu Beach at the southeast coasts of Aegean Sea. Samples were collected from 6 stations in Dalyan Beach between 2012 and 2016. We report here on the occurrence of 9 genera including, Catenula Mereschkowsky, Cymatosira Grunow, Dimeregramma Ralfs, Diplomenora Blazé, Eunotogramma Weisse, Meloneis Louvrou, Danielidis & Economou-Amilli, Neohuttonia Kuntze, Plagiogramma Greville and Tetramphora Mereschkowsky, as well as 40 taxa as newly-recorded from Turkey. The newly-recorded diatoms are characterized in terms of their morphology and illustrated with light micrographs. For each species, their habitat and geographic distribution along the coasts are discussed

Diatom Diversity and Community Structure Along a Thermal Gradient in the Maple River of Northern Michigan

Articlehttp://deepblue.lib.umich.edu/bitstream/2027.42/96973/1/UMURF-Issue04_2007-AMaguire.pd

Epilithic diatoms (Bacillariophyta) from cloud forest and alpine streams in Bolivia, South America II: A preliminary report on the diatoms from Sorata, Department of La Paz

Un total de siete muestras de epiHton fueron colectadas en rios dentro de ungradiente altitudinal en el bosque nublado de Bokvia, cerca de la capital La Paz. Laflora diatomologica es diversa v no se encontraron patrones altitudinales claros. Talflora esta compuesta por especies cosmopolitas y taxa restringidos a los Andes con losgeneros Gompbonema, Nit^schia, Engonopsis v Engonema agrupando al mayor numero deespecies e individuos con mayores frecuencias. La flora esta tambien representada porvarios taxa alcalifilos y alcaKbiontes, reflejando los altos valores de pH de los rios. Las caracteristicas de los sitios muestreados, asi como una lista de taxa y figurasrepresentativas se presentan en este trabajo

Historical and Current Perspectives on the Systematics of the ‘Enigmatic’ Diatom Genus Rhoicosphenia (Bacillariophyta), with Single and Multi-Molecular Marker and Morphological Analyses and Discussion on the Monophyly of ‘Monoraphid’ Diatoms

This study seeks to determine the phylogenetic position of the diatom genus Rhoicosphenia. Currently, four hypotheses based on the morphology of the siliceous valve and its various ultrastructural components, sexual reproduction, and chloroplasts have been proposed. Two previous morphological studies have tentatively placed Rhoicosphenia near members of the Achnanthidiaceae and Gomphonemataceae, and no molecular studies have been completed. The position of Rhoicosphenia as sister to &lsquo;monoraphid&rsquo; diatoms is problematic due to the apparent non-monophyly of that group, so hypotheses of &lsquo;monoraphid&rsquo; monophyly are also tested. Using an analysis of morphological and cytological features, as well as sequences from three genes, SSU, LSU, and rbcL, recovered from several freshwater Rhoicosphenia populations that have similar morphology to Rhoicosphenia abbreviata (Agardh) Lange-Bertalot, we have analyzed the phylogenetic position of Rhoicosphenia in the context of raphid diatoms. Further, we have used topology testing to determine the statistical likelihoods of these relationships. The hypothesis that Rhoicosphenia is a member of the Achnanthidiaceae cannot be rejected, while the hypothesis that it is a member of the Gomphonemataceae can be rejected. In our analyses, members of the Achnanthidiaceae are basal to Rhoicosphenia, and Rhoicosphenia is basal to the Cymbellales, or a basal member of the Cymbellales, which includes the Gomphonemataceae. Hypothesis testing rejects the monophyly of &lsquo;monoraphid&rsquo; diatoms.</p

Biogeography of the cosmopolitan terrestrial diatom Hantzschia amphioxys sensu lato based on molecular and morphological data

Until now, the reported diversity of representatives from the genus Hantzschia inhabiting soils from different parts of Eurasia was limited to the few species H. amphioxys, H. elongata and H. vivax and some of their infraspecific taxa. We have studied the morphology, ultrastructure and phylogeny of 25 soil diatom strains, which according to published description would be assigned to "H. amphioxys sensu lato" using 18S rDNA, 28S rDNA and rbcL. We show that strains are made up of seven different species of Hantzschia, including five new for science. Five strains were identified as H. abundans. This species has a slight curvature of the raphe near its external proximal ends. Four of the examined strains were represented by different populations of H. amphioxys and their morphological characteristics fully correspond with its isolectotype and epitype. The main specific features of this species include 21-25 striae in 10 mu m, 6-11 fibulae in 10 mu m, 40-50 areolae in 10 mu m and internal proximal raphe endings bent in opposite directions. H. attractiva sp. nov., H. belgica sp. nov., H. parva sp. nov., H. pseudomongolica sp. nov. and H. stepposa sp. nov. were described based on differences in the shape of the valves, significant differences in dimensions, a lower number of striae and areolae in 10 mu m and the degree and direction of deflection of the internal central raphe endings. Based on the study of the morphological variability and phylogeny of soil Hantzschia-species from different geographical locations we conclude that while some species such as H. amphioxys are truly cosmopolitan in their distributions, some sympatric populations of pseudocryptic taxa exist in the Holarctic

HANTZSCHIA SUBANDINA FRENGUELLI (BACILLARIOPHYCEAE): MORPHOLOGY, STATUS AND TYPIFICATION, AS WELL AS THE DESCRIPTION OF A NEW SPECIES OF NITZSCHIA

Backgrounds and aims: Hantzschia Grunow is a genus characterized by having valves asymmetric to the apical axis, markedly dorsiventral, with an eccentric raphe on the ventral side supported by fibulae and &lsquo;hantzschioid&rsquo; symmetry of the frustules. In 1942 J. Frenguelli published the flora of diatoms of Neuqu&eacute;n province (Argentina), work in which he erected Hantzschia subandina as a new species for science. This work investigates the identity and taxonomic status of this taxon. M&amp;M: Original material of Hantzschia subandina of the Frenguelli Collection was analysed with light and scanning electron microscopy. Results: Observations on the material suggested two different species were included in the concept of this species assigned originally to the genus Hantzschia. Furthermore, neither of the two species present are assignable to the genus Hantzschia. Nitzschia subandina (Frenguelli) comb. nov. has a large central nodule and a slight asymmetry about the apical axis; it also produces frustules with nitzschioid and hantzschioid symmetry. We designate a lectotype for this taxon. In addition, another diatom in the same material with slight asymmetry about the apical axis has distinctive ornamentation on the mantle of the valve and produces nitzschioid and hantzschioid frustules. For this taxon we tentatively assign it to the non-monophyletic genus Nitzschia, describing it as N. araucana sp. nov. We discuss the possible phylogenetic position of this new taxon, and suggest that the genus Nitzschia is &ldquo;the next Navicula&rdquo; ready to be further subdivided into distinct genera. &nbsp; Resumen Introducci&oacute;n y objetivos: Hantzschia Grunow es un g&eacute;nero de diatomeas caracterizado por la asimetr&iacute;a dorsiventral de sus valvas, rafe soportado por f&iacute;bulas sobre el margen ventral, y simetr&iacute;a hatzschioide de los fr&uacute;stulos. En 1942 J. Frenguelli public&oacute; la flora de diatomeas de la provincia de Neuqu&eacute;n (Argentina), obra en la que erigi&oacute; a Hantzschia subandina como una nueva especie para la ciencia. El objetivo de este trabajo es analizar la identidad de este tax&oacute;n y su status taxon&oacute;mico.&nbsp; M&amp;M: El material original de Hantzschia subandina, presente en la Colecci&oacute;n Frenguelli depositada en el Herbario de la Divisi&oacute;n Ficolog&iacute;a del Museo de La Plata, fue analizado con microscop&iacute;as &oacute;ptica y electr&oacute;nica de barrido. Resultados &amp; Conclusiones: la observaci&oacute;n del material original de Hantzschia subandina sugiere que dos entidades distintas fueron incluidas en el concepto de esta especie. Ambas producen fr&uacute;stulos tanto con simetr&iacute;a nitzschiode como hantzschioide, por lo que ninguna de ellas pertenece al g&eacute;nero Hantzschia. La primera presenta un n&oacute;dulo central conspicuo y leve asimetr&iacute;a seg&uacute;n el eje apical; consideramos que estos ejemplares corresponden a Nitzschia subandina (Frenguelli) comb. nov., y realizamos la enmienda y lectotipificaci&oacute;n del tax&oacute;n. La segunda entidad presente en el mismo material, posee una leve asimetr&iacute;a seg&uacute;n el eje apical, y una distintiva ornamentaci&oacute;n en el manto valvar; hemos asignado este tax&oacute;n al g&eacute;nero Nitzschia, describiendo N. araucana sp. nov. Discutimos la posible posici&oacute;n filogen&eacute;tica de este nuevo tax&oacute;n dentro de Nitzschia, g&eacute;nero polifil&eacute;tico que requiere de una profunda revisi&oacute;n y subdivisi&oacute;n en g&eacute;neros, tal como ocurri&oacute; con el g&eacute;nero Navicula. </section

Epilithic diatoms (Bacillariophyta) from cloud forest and alpine streams in Bolivia, South America 3: diatoms from Sehuencas, Carrasco National Park, Department of Cochabamba

Studies on Bolivian diatoms are scarce and they do not represent the great geographic variability of the country. One of the regions with the highest biological diversity in Bolivia is the Yungas (cloud forest), a 90.500 km2 strip located between the Andean Puna and the Amazonian lowlands. The Carrasco National Park is the park with the largest extension of Yungas within its boundaries. This park is located east from Cochabamba, the third largest city in Bolivia, and has an area of ca 6.226 km2, serving as a refuge to 5.000 recorded species of plants and more than 300 species of vertebrates. Very little is known about the aquatic biota in the zone and there are no studies on diatoms. One of the preferred tourist spots within the park is Sehuencas, located 17°31\u2742" S and 65°16\u2717" W and characterized by numerous lotic waterbodies. The present work was carried on 5 epilithic samples from which 118 species, varieties and forms were identified using light (LM) and scanning electron microscopy (SEM). Forty-two (36%) of these taxa were not found in the literature for South America or other regions of the world. This high percentage of unknown taxa suggests a high potential for the contribution of new organisms to science, many of which are possibly endemic to the region, thus justifying an additional effort to preserve the aquatic habitats in the park. Two new species are described herein (Fragilaria cochabambina Morales sp. nov. and Achnanthidium sehuencoensis Morales.sp. nov.) and comparisons with published morphologically similar taxa are presented. Unknowns remain undescribed until larger populations that allow detailed LM and SEM studies are found

Taxonomy and valve morphology of Humidophila species (Bacillariophyceae) from aerophilous habitats in northeastern Argentina, with the description of four new species

During a survey of the diatoms present in aerophilic microhabitats associated with waterfalls in Misiones Province (Argentina), mainly within Iguazú National Park (N.P.), seventeen taxa belonging to the genus Humidophila have been recorded. Previously, only six species of the genus have been reported for all of Argentina. Of the seventeen taxa considered here, four exhibit a unique combination of features and are pro-posed as new species. These are H. iguazuensis sp. nov., H. lagartiensis sp. nov., H. misionera sp. nov. and H. sebastianii sp. nov. An additional six previously–described species (H. arcuatoides, H. contenta, H. nienta, H. parallela, H. platensis and H. subtropica) are reported. Of these previously–described taxa, only H. contenta has been reported previously from Argentina, so the occurrences of the others in the region expand their known geographic distributions. One taxon has been tentatively identified (as Humidophila aff. biscutella) and the remaining six taxa observed are presumed to be new but remain unidentified at the species level because they occurred in small numbers and could not be sufficiently documented for formal description. This is currently the largest concentration of Humidophila taxa reported in a relatively small geographic region anywhere in the world. Morphological features among the species of the genus are discussed, and we describe the structure of the features associated with longitudinal tubes in the genus. We also present and describe the ecological and biogeographic distributions of Humidophila species.Fil: Vouilloud, Amelia Alejandra Beatriz. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; ArgentinaFil: Guerrero, José María. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; ArgentinaFil: Sala, Silvia Estela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; ArgentinaFil: Simonato, Julián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; ArgentinaFil: Kociolek, John Patrick. State University of Colorado at Boulder; Estados Unido

Encyonopsis indonesica sp. nov. (Bacillariophyceae, Cymbellales), a new diatom from the ancient lake Matano (Sulawesi, Indonesia)

A new species, Encyonopsis indonesica, is described from the ancient lake Matano, Sulawesi island, Indonesia. The morphology of this species was studied by means of light and scanning electron microscopy. E. indonesica has a remarkable valve ultrastructure. The valve surface is ornamented with numerous longitudinal siliceous ribs and siliceous verrucae. Valve face delineated from the mantle by a thickened marginal ridge. Raised sterna border the raphe branches. Raphe is distinctly undulate with distal ends hooked strongly to the ventral side. The only similar species to E. indonesica is Amphora dissimilis described from New Caledonia. Comparison of both taxa is given and A. dissimilis is transferred to Encyonopsis. The taxonomic placement of both taxa is evaluated, and the phenomenon of external siliceous ornamentation is discussed. </div