Kelp is a large form of brown algae that make up the order Laminariales. They can be found in “underwater forests” in shallow oceans.
Kelp thrives in cold, nutrient-rich waters. Because kelp attaches to the seafloor and eventually grows to the water’s surface and relies on sunlight to generate food and energy, kelp forests are always coastal and require shallow, relatively clear water. Generally speaking, kelps live further from the tropics than coral reefs, mangrove forests, and seagrass beds, so kelp forests do not overlap with those systems. Like those systems, though, kelp forests provide important three-dimensional, underwater habitat that is home to hundreds or thousands of species of invertebrates, fishes, and other algae. Some species aggregate and spawn in kelp forests or utilize these areas as juvenile nursery habitat. Large species of sharks and marine mammals are known to hunt in the long corridors that form in kelp forests between kelp.
In most kelp plants, the body consists of flat leaf-like structures known as blades. The blades come from the long stem-like structures. The holdfast, a root-like structure keeps the kelp stuck to the seafloor. Gas-filled bladders form in the blades of American species to hold the blades close to the water’s surface.
Growth occurs at the base of the meristem, where the blades and stem meet. Growth may be limited by grazing. Sea urchins, for example, can make entire areas into urchin barrens.