One adaptation of seaweed is that some types of seaweed, such as kelp, have holdfasts instead of roots. Holdfasts grab on to a substrate, such as a rock, and keep the seaweed from washing away during storms. Seaweed also have pnuemocysts, or gas bladders, that keep the fronds afloat.
Though kelp forests can be as high as 200 feet, some seaweed live in shallow tidal pools. Because of this, they must adapt to fluctuations in the temperature, currents and salinity of the water. Some types of seaweed have adapted to brief dry periods when the tide is low. Sargassum, a type of seaweed that lives in the Sargasso Sea, has no holdfast, it simply floats in the water.
Undaria, which is the species of the edible wakame seaweed, has found a way to spread by clinging to the hulls of boats and letting the boats take it to places where it can become extremely invasive. Sometimes, undaria becomes so rampant that it blocks out the sunlight necessary for other life forms in the ocean.
Seaweed is a type of algae, and it releases spores instead of seeds into the water. The water helps the spores disperse throughout the ocean. The spores then turn into sperm and eggs that join and form zygotes.