Phytoplankton serves as food for virtually all the organisms living in an aquatic environment. It is a primary food producer and serves as the foundation of aquatic food web. If there is a decline in the amount of phytoplankton, the organisms which feed directly on the plant may reduce significantly as a result of dire competition for food, this in turn will affect the organisms which feed on the dying out organisms and the trend will move in a similar way until it affect all the organisms living in that particular aquatic habitat.
