Algae
Green algae
Algae are a very large and diverse group of simple, autotrophic organisms. There are unicellular and multicellular forms of algae. There are many types of algae. There are red algae, brown algae, and blue-green algae. As algae makes food, it releases oxygen into the water, but when it becomes overabundant, decaying algae depletes oxygen levels. To the left is a picture of the most common algae, green algae. There are more than 7000 species growing in different areas. It's a paraphyletic group since it doesnt include the Plantae. An example of a marine species of algae is sea lettuce (Ulva).