ABSTRACT
The phytoplankton of lakes, estuaries and oceans is composed of singlecelled algae. Cells of the plankton algae are largely microscopic in size ranging from a few microns to a few hundred microns in the longest dimension. Species may occur as single cells, or as colonies or filaments composed of many cells. The colonies/filaments of some species are often visible to the naked eye. For example, spherical colonies of the cyanobacterium Gloeotrichia are https://www.w3.org/1998/Math/MathML">≈1mmhttps://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429078446/6a86b31b-6da8-4e2c-b426-c23b1310df4c/content/eq542.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> in diameter and clearly visible. The filamentous cyanobacterium Aphanizomenon forms bundles of thichomes (filaments) that appear as grass clippings in the water. The phytoplankton are sometimes grouped by size into ultra-, nano- and net plankton (those caught with a net), with respective separations at about 10 and https://www.w3.org/1998/Math/MathML">50μmhttps://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429078446/6a86b31b-6da8-4e2c-b426-c23b1310df4c/content/eq543.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Wetzel, 1983). Phytoplankton are usually quantified by microscopic analysis of preserved water samples, rather than net samples, because of the significance of nanoplankton.
