Phytobenthos are subcategorized into microphytobenthos and macrophytobenthos. Microphytobenthos such as diatoms can be as small as 0.2 μm in diameter, and macrophytobenthos such as kelps can be tens of meters long. To establish themselves on surfaces, phytobenthos usually stabilize themselves onto substrates through the use of various polysaccharides, glycoproteins, and even lipids that make up the extracellular polymeric substance, of which 40 - 90% of the carbons are derived from carbohydrates. Some species of phytobenthos such as Ostreobium and diatoms such as the Synedra acus Kütznig have been observed to live in a free-living state. Benthic diatoms have been found to be useful indicator species for determining the state of the aquatic environment as many study models have demonstrated association between the type of diatom communities that are present and the stability and the size of the sediments. Non-diatom phytobenthos such as the cyanobacteria Nostoc spp. and Phormidium spp. have also been used as biological indicators.