Algae are found in bodies of fresh and salt water across the globe. They can also grow on rocks and trees and in soil when enough moisture is available. Most algae are able to make energy from sunlight, like plants do. They produce a large amount of the oxygen we breathe. However, at some stages of their lives, some algae get their nutrients from other living things.
Some dinoflagellates make their own energy from sunlight, like plants.
But others like Pfiesteria produce toxic substances that stun passing fish and cause bleeding sores. The Piesteria then feed on the fish blood and fluids. They have hard shells made out of silica, or glass. When they die, these shells sink to the bottom of their watery environments. We mine deposits of these silica shells that formed hundreds of thousands of years ago to make abrasives, shiny road paint and grit in toothpaste.