Among the thousands of species of microscopic algae at the base of the food chain, a few dozen produce toxins. These algae make their presence known during what is referred to as a "harmful algal bloom," or HAB. A HAB event may discolor the water, and are often called "red tides," but they frequently appear green, yellow, or brown, depending on the algae. Other species bloom in dilute, inconspicuous concentrations but are noticed because they produce potent toxins that kill marine organisms, or transfer through the food chain, harming organisms at multiple levels.
The causes of HAB events are poorly understood, but possible explanations range from natural mechanisms of species dispersal to anthropogenic actions such as nutrient loading, climatic shifts, or transport of algal species via ship ballast water.
HAB events now affect virtually every coastal area, an escalating and worrisome trend. As the impacts of mass mortalities of wild and farmed fish, marine mammals, seabirds, and illness and death in humans from contaminated fish or shellfish increase, research about the mechanisms of HAB events is urgently needed. See NOAA's National Ocean Service's site Harmful Algal Blooms: Tiny Organisms with a Toxic Punch for more extensive information.
Sea-Bird Scientific builds absorption meters, scattering meters, and fluorometers that identify, characterize, and determine components of harmful algal blooms.