Harmful algae are microscopic,single-celled plants that live in the sea.
Most species of algae or phytoplankton are not harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist. Unfortunately, a small number of species produce potent neurotoxins that can be transfered through the food web where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish , birds , marine mammals , and even humans that feed either directly or indirectly on them. Scientists now prefer the term, HAB, to refer to bloom phenomenon that contain toxins or that cause negative impacts.