Some varieties of seaweed, like kelp, contain holdfasts in place of roots, which is one adaption of seaweed. Holdfasts secure the seaweed to a surface, such a rock, and prevent it from washing away during storms. Pneumocysts, or gas bladders, are another feature of seaweed that keep the fronds afloat.

Some seaweed lives in shallow tidal pools despite kelp forests reaching heights of 200 feet. They must therefore adjust to changes in the water’s salinity, currents, and temperature. Some varieties of seaweed have evolved to survive brief dry intervals at low tide. The Sargasso Sea is home to a particular form of seaweed known as sargassum, which floats in the water without a holdfast.

The edible wakame seaweed species, Undaria, has discovered a way to spread by adhering to the hulls of boats and allowing the boats to transport it to locations where it can become very invasive. Undaria can occasionally become so overgrown that it obstructs the sunlight needed for marine life.

Seaweed is a form of algae, and it disperses spores into the sea as opposed to seeds. The water aids in the spores’ oceanic sporulation. After that, the spores develop into sperm and eggs, which combine to form zygotes.