A plankton net is used to concentrate plankton in a water sample. The net's mesh is chosen to retain plankton of a desired size; a common mesh size for retaining many protoplankton and phytoplankton is 28 micrometers. Zooplankton will also be retained in samples from this size mesh net, but many small protoplankton, phytoplankton, and bacterioplankton will slip though and be lost. Experts use other methods to collect these small plankton members and to count them.