text: Kelp fronds and pneumatocysts. Pneumatocysts, gas-filled bladders, float the kelp plant off the ocean bottom toward the surface and sunlight, where the leaf-like blades and stipes of the kelp plant grow fastest. Giant kelp can grow up to 2' in a single day given optimal conditions. Epic submarine forests of kelp grow throughout California's Southern Channel Islands. San Clemente Island, USA, Macrocystis pyrifera, natural history stock photograph, photo id 34604