An improved coverslip method for investigating epipelic diatoms

Abstract

The traditional coverslip method for harvesting motile diatoms was improved and standardized by determining optimum times for diatom harvesting; by using opaque Petri dish bases as experimental chambers; and by preparing coverslips by burning. Three experiments were conducted to evaluate the harvesting efficiency of the coverslip method. Experiment 1 was performed to reveal the spatial distribution of epipelic diatoms on the coverslips after exposure periods ranging from 2 to 36 h. The transect count results were supplemented using an Inverse Distance Weighted algorithm and showed that after 8 h exposure the epipelic diatoms began to accumulate at the coverslip margin. Therefore, 8 h was identified as the optimum time for the coverslip method to capture epipelic diatoms efficiently for the samples. However, the optimum time could vary between sites because of differences in diatom composition, light intensity and other environmental conditions. Experiment 2 revealed that the numbers of epipelic diatoms harvested from opaque chambers were 15.6% higher than those harvested from transparent chambers, indicating that opaque sides and base reduce multi-directional diatom migration. Experiment 3 indicated that the burning method was more efficient than the traditional method (directly counting fresh diatoms) because it makes identification easier and yields higher densities of diatoms. All experiments demonstrated that the coverslip method harvested more epipelic diatoms, made identification easier than the traditional method, enabling permanent slides to be created. In addition, the method makes it possible to estimate in situ epipelic cell densities, if the sediment area is known.

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