Seaweed serves as food and shelter for numerous marine animals. Limu is a Hawaiian word that means plants that live underwater or in damp areas. For most people in Hawaii, Limu is a common name used in place of seaweed. Algae and seaweed are almost the same thing, because they are both aquatic nonvasculars (they don't have a circulatory system like land plants). Since water and nutrients are around the algae they absorb it through its blades.
There are about 420 species of marine algae that grow in Hawaii's waters. Only 13 of 420 are endemic to Hawaii, which means that 13 species of seaweed are only found here in Hawaii. Seaweed comes in many different colors, shapes, and sizes. Scientist separate seaweeds by color: red (Rhodophyta), brown (Phaeophyta), blue green (Cyanophyta), and green (Cholorophyta). Seaweed is a plant without roots or stems. Seaweeds hold onto rocks by sticking its tissues onto the rocks.
In old Hawaiian days limu was the third ingredient to a balanced diet of fish and poi (a paste made from cooked taro plant). This would keep the Hawaiians healthy. The Hawaiians used 60 to 70 species of seaweed for medicine, ceremonies, leis, and also for food. There are local recipes that use seaweed and many nationalities use them in cooking. Some favorite limu that people pick at low tides are getting over picked and are becoming very scarce.