Planktonic organisms dominate waters in ponds, lakes and oceans. Because of their short life cycles, plankters respond quickly to environmental changes and the variability in their density and composition are more likely to indicate the quality of the water mass in which they are found. Planktonic community is formed by numerous organisms from distinct taxonomic position, ranging from 0.2μm up to 2mm. Despite others, the light microscopy is the most used apparatus to enumerate these organisms and different techniques are necessary to cover differences in morphology and size. Here we present some of the main light microscopy methods used to quantify different components of planktonic communities, such as virus, bacteria, algae and animals.
