Tabellaria

Abstract: SUMMARY The taxonomy, distribution, and ecology of the diatom genus Tabellaria Ehr. from a portion of the northcentral United States were studied from collections made from August 1968 to October 1971. Using the transmission electron microscope with carbon replicas of the frustule surfaces, taxonomically significant characters were identified and related to those visible with the light microscope, four morphologically distinguishable taxa were recognized. The frustular morphology of T. fenestrata (Lyngbye) kutz. em. Knudson var. fenestrata was confirmed by both light and electron microscopy. T. flocculosa (Roth) Kutz. var. flocculosa is composed of 3 morphologically distinguishable strains. One of which is sufficiently different from the nominate variety to be described as T. flocculosa var. linearis var. nov. Also, a planktonic ecotype of one of the strains was identified.

Abstract: Field survey of algae and cyanobacteria from terrestrial and freshwater habitats in the vicinity of arctic Ny-Alesund, Svalbard (790N) (high Arctic sea area) was performed in June 2006. Species diversity and abundance were evaluated by using epifluorescence microscopy and culturing methods. In total, 29 taxa in 25 genera were identified, of which Leptolyngbya spp., Trichormus sp. and Chlamydomonas nivalis were abundantly present in almost every sample. In several locations, blooms were formed by species C. nivalis, Scotiellopsis sp., Klebsormidium flaccidum, Zygnema sp., Meridion circulare, Tabellaria fenestrata and Fragilaria sp. Eleven new species from this locality are described.

Abstract: Single-species, steady-state chemostat cultures of two freshwater diatoms showed that Fragilaria crotonensis had a lower equilibrial requirement for silicate than did Tabellaria fenestratra. Using this information, resource competition theory predicts that Fragilaria should be able to invade silicate-limited equilibrium populations of Tabellaria, but Tabellaria should not be able to invade silicatelimited Fragilaria. This prediction was supported by a series of invasion experiments. The two species did not have detectable differences in their phosphate requirements. Invasion experiments showed that Fragilaria could invade Tabellaria cultures, but that Tabellaria could not invade Fragilaria cultures under phosphate-limited conditions. These results are consistent with predictions based on previous studies of the phosphate physiology of these genera.

Abstract: Fossil diatom assemblages from the sediment/water interface in 105 Minnesota lakes were compared with measurements of alkalinity, sulphate, total phosphorus, transparency, and water depth at the sample site. Similar assemblages were placed together using cluster analysis and comparisons of environmental variables between diatom clusters were made using an analysis of variance. Total alkalinity and transparency showed the greatest difference among clusters. Samples from shallow eutrophic prairie lakes were dominated by Melosira granulata, Stephanodiscus niagarae and, occasionally, by Stephanodiscus hantzschii. Deep oligotrophic lakes had modest percentages of Cyclotella comta. Dilute acid lakes were dominated either by Melosira distans and M. italica or by Tabellaria fenestrata, Cyclotella stelligera, and in some cases C. glomerata. Assemblages with Cyclotella glomerata and Synedra nana were found in naturally meromictic lakes. Stephanodiscus hantzschii showed a preference for extremely eutrophic lakes. The relationships between recently deposited diatom assemblages and the lake environmental conditions studied here can be used to evaluate the extent of past environmental change in lakes.