University of Southern California Sea Grant Program

Help with Kelp

What's that waving back and forth in the ocean? It looks like a tree - a tree in the ocean?! No, it's kelp! Kelp is a type of marine algae, or seaweed. Seaweeds come in three different color varieties, red, green and brown. Kelp is a kind of brown seaweed that grows to be very large. Although kelp resembles a kind of weed or tree, it is quite different from plants that grow on land. First of all, kelp has no roots. Kelp does have a way to anchor itself to the bottom of the ocean floor, but this anchoring system, called the holdfast, does not take in nutrients like plant roots do. The other parts of the kelp also have different names. The "leaves" of a kelp plant are called blades and the "stem" is called the stipe. Another structure unique to kelp is the air bladder, which looks like a small balloon at the base of each blade. The stipe of the kelp is very flexible and cannot stand up on its own - the air bladders help the stipe and blades of the kelp float in the water, which allows the kelp plant to grow up toward the surface of the water, where the sunshine is brightest.