Artificial surfaces as a method of studying populations of benthic micro-algae in fresh water

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Abstract
Most work on the ecology of communities of attached algae has involved the investigation of populations which develop on artificial surfaces exposed in the water for a known period of time. The nature and position of the surface and length of time of exposure have been shown to influence the population which develops. No studies have related the structure of these populations to populations on natural surfaces. Microscope slides which had been exposed in a pond and a stream for two and four weeks were sampled over a period of more than one year, and natural vegetation was sampled at the same time. The populations of attached diatoms on each substrate were analysed. The diatoms in the pond grew mainly in summer on the slides and in winter on the natural host. In the stream the main growth of the population was over the summer period in all cases. There were twice as many species of diatoms growing on natural hosts as on the slides, and the percentage importance of the species was different. The time of year at which some species grew was different on the slides and the natural vegetation. It was concluded that under these conditions the use of artificial surfaces is not a valid ecological method.