Most animal plankton (zooplankton) and plant plankton (phytoplankton) live several months, but some species may live for more than a year. However, there are thousands of species of plankton, making it impossible to pinpoint a specific average life span that can apply to all plankton species.
To a large extent, the lifespan of a plankton species depends on the size of the organism. Single-celled plankton reproduce by cell division. Thus, it can be said that the cells never truly die. However, the one-celled plankton divide as frequently as every few hours up to every few days, depending on the growth conditions and the species.