The plankton light reactor is a simple system for the production of plankton in a natural food chain. In the plankton light reactor, microalgae are produced with light, fertilizer and CO2. The microalgae can be fed directly to many filter-feeding invertebrates, and especially to zooplankton. The growth rate of the microalgae in the plankton light reactor is enormous. If the supply of light, CO2 and nutrients is continuous, the bio-mass of the algae may increase four-fold within 24 hours. Fresh and salt water species of phytoplankton can be cultivated.