Ice algae terrestrial ice algae occur in freshwater systems, the species composition differs greatly from that of sea ice algae. These communities are significant in that they often change the color of glaciers and ice sheets, impacting the reflectivity of the ice itself. Microbial life in sea ice is extremely diverse, and includes abundant algae, bacteria and protozoa. Algae in particular dominate the sympagic environment, with estimates of more than 1000 unicellular eukaryotes found to associate with sea ice in the Arctic. Species composition and diversity vary based on location, ice type, and irradiance. In general, pennate diatoms such as "Nitschia frigida"
Bacteria sizes, called morphologies. Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0.5–5.0 micrometres in length. However, a few species are visible to the unaided eye—for example, "Thiomargarita namibiensis" is up to half a millimetre long and "Epulopiscium fishelsoni" reaches 0.7 mm. Among the smallest bacteria are members of the genus "Mycoplasma", which measure only 0.3 micrometres, as small as the largest viruses. Some bacteria may be even smaller, but these ultramicrobacteria are not well-studied. Most bacterial species are either spherical, called "cocci" ("sing". coccus, from Greek "kókkos", grain, seed), or rod-shaped, called "bacilli" ("sing". bacillus,