Harmful algal bloom
Harmful algal blooms or HABs are algal blooms composed of phytoplankton known to naturally produce biotoxins, they can occur when certain types of microscopic algae grow quickly in water, forming visible patches that may harm the health of the environment, plants, or animals. HABs can deplete the oxygen and block the sunlight that other organisms need to live, and some HAB-causing algae release toxins that are dangerous to animals and humans. HAB can occur in marine, estuarine, and fresh waters.
The frequency and intensity of recorded harmful algal blooms has increased worldwide over the past decades. The reason for this is often assumed to be eutrophication. However, many other explanations are possible, for example increased transport of algae with ship ballast water or increased monitoring efforts. For management purposes it is important to understand which are the main factors controlling the risk of harmful algal blooms. For a long time, a link was made between high nutrient concentrations and harmful algal blooms. More recently, researchers point out the importance of interacting biological and physical processes, including effects of wind, currents and water temperature.