The bladder on kelp, known as a pneumatocyst, serves to provide buoyancy, allowing the kelp to float towards the surface of the water. This positioning enables the kelp to access sunlight for photosynthesis, which is essential for its growth and energy production. Additionally, being elevated in the water column helps the kelp maximize its exposure to nutrients in the surrounding water.
Most macroalgae (multicellular algae) are made up of three parts. The blade is a leaf-like structure that captures light and carries on photosynthesis. The stipe is the stem of the algae. The holdfast is the anchor for the algae; it holds the algae to a solid surface such as a rock or pier. Although the holdfast may look like roots, it does not function to get nutrients or water. Some algae may have a fourth structure, the pneumatocyst; this structure is an air bladder on the stipe or blade that functions to keep the algae afloat in the water column.