In freshwater and marine environments, algae consist of a variety of unicellular (microalgae) as well as multicellular forms (macroalgae) of photosynthetic organisms. In general, macroalgae are multicellular, autotrophic organisms with no roots, stems, or leaves, currently classified as green (chlorophyceae), red (rhodophyceae), or brown (phaeophyceae). Those characteristics make these organisms important to the primary production of aquifer systems; they are also CO² fixers, which have a dramatic impact on coastal ecosystems, supplying habitat and food for a variety of marine animals.