A close view of Ulva. You will find that each of these algae are very particular about where they live. Each algae survives best in its own little niche. The upper tide pool algae have adapted to extremes in salt, temperatures and exposure to the sun. The brown and red algae, that are mostly in the lower pools, have adapted to being submerged beneath the pounding waves for long hours.
Land plants root themselves into the ground.
You know from standing on the shore, that the sand is removed right out from under your feet when a wave goes back out to sea. Some algae has adapted to this by developing a root like structure called a holdfast. This mass of finger like roots, hold on with a grip so tight that even the toughest pounding of surf can't break it loose. It will hold onto rocks, pipes, or even mussel shells. The blades of the algae as well as most of the body are photosynthetic.