Any drifting organism that inhabits oceans or fresh waterOne of the most important organisms on Earth due to food supply they provide to most aquatic life. Plankton. Phytoplankton. The autotrophic component of plankton (or the ones who can produce their own food). Algae. Defined as organisms belonging in one of seven specific phyla or divisionsChlorophytaRhodophytaPhaeophytaDinophytaBacillariophytaEuglenophytaChrysophyta.