Communities of large brown algae, called kelp, support evolving marine life, such as sea otters, as well as established groups of fishes and invertebrates. Though kelp is a plant, it is not closely related to its land counterparts. For one thing, its cells use different pigments for photosynthesis. Kelp grows in cool, shallow waters, where it attaches to rocks and coral or sometimes floats freely. Because marine plants do not preserve well over time, scientists can date kelp only to the Miocene, when animals it supports are known to appear, but it may exist in earlier periods.