Experiments with Mixed Populations of Benthic Estuarine Diatoms in Laboratory Microecosystems

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Abstract
Samples of sediment from the intertidal flats of the Dutch Wadden Sea were transferred to the laboratory and the temporal variations in their vegetations of benthic diatoms investigated. Microecosystems from widely different localities were used. The density (as chlorophyll a measurements) and species composition [Navicula arenaria, N. digito-radiata, N. flanatica, Nitzschia sigma, N. closterium, Amphiprora sp., Surrirella gemma, Cylindrotheca sp. and Amphora sp.] were determined for periods from 4 to 23 wk. Fluctuations in density and a clear succession of species were apparent in most of the experiments. Grazing of ciliates was responsible for a decrease in the density and a change in the species composition of the benthic diatom flora. The influence of silicate concentration and diffusion of nutrients from deeper sediment layers was evident in part of the experiments. The addition of nitrate, phosphate and wastewater from a sugarmill had no effect in the concentrations used. A dense vegetation of 3 diatom spp. [N. arenaria, Amphiprora sp. and N. digito-radiata] flourished in a microecosystem collected from deposits near a municipal sewage outfall.