The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column are called phytoplankton. They provide the food base for most marine food chains. Kelp grows mostly in shallow marine waters. Some are used as human food or harvested for agar or fertilizer. Kelp can grow in large stands called kelp forests. These forests prevent some of the damage from waves. Many different species live in them, including sea urchins, sea otters, and abalone.