How many species of algae are there?

There are 7000 of them, most of whom live near the shore where they can cling to the rocks or the bottom with a special foot. Attached to this foot, the fronds oscillate in the water. 
Most brown algae live in cold waters and some become huge. 
Red algae are more prevalent in warm waters. 
The blue algae live in hot or cold waters * The branches of the seaweed are called fronds. Some have vesicles that help them float.