Ecology of the Epiphytic Diatom Tabellaria Flocculosa (Roth) Kutz. Var. Flocculosa in Three English Lakes

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Abstract
Estimations were made of the population density of this non-motile colonial diatom on the vertical submerged shoots of Phragmites communis and Schoenoplectus lacustris. Samples were collected at frequent intervals from 3 lakes in the English Lake District for periods up to 4 years. Samples were collected at known lake levels and from known depths. A new apparatus for cutting reeds at known depths is described. The range of population density of the diatom was 1 to about 4500 cells/mm2 plant surface. A mean increase rate of 1.3 vegetative divisions per week for 7.5 weeks was recorded. When growth conditions were favorable, grazing, parasitism and wave action had little effect on population density. A mean decrease rate equivalent to a loss of 3.5 divisions per week was maintained for 3.5 weeks when adverse nutrient conditions were arresting growth. The seasonal cycle varied in different lakes and sometimes in the same lake in different years.