This Giant Seaweed Can Grow Taller Than A 10-Story Building! 🌊 Bull kelp is one of the fastest-growing seaweeds on Earth and can reach an incredible 100 feet (30 meters) in length! It begins life anchored to rocks by a tangled, root-like structure called a holdfast. Although it resembles roots—or even a brain—it doesn’t absorb nutrients like plant roots. Instead, its job is simply to keep the kelp firmly attached against powerful ocean waves. A gas-filled bulb, known as a pneumatocyst, acts lik