This coral has extended its delicate polyps to feed on the abundant plankton during the night. The green coloration in the polyps comes from a symbiotic algae known as zooxanthellae. This symbiotic algae lives inside the coral polyp tissues and uses sunlight to produce extra food for the coral during the day. It also produces oxygen and helps the coral to remove waste products. Corals are filter feeders. They extend their tentacles to capture plankton and other scraps of food that float by in the current.