Distribution of HABs
Virtually every coastal country in the world is affected by harmful algal blooms (HABs). These include blooms of toxic, microscopic algae that lead to illness and death in humans, fish, seabirds, marine mammals, and other oceanic life. There are also non-toxic HABs that cause damage to ecosystems, fisheries resources, and recreational facilities, often due to the sheer biomass of the accumulated algae. The term “HAB” also applies to non-toxic macroalgae (seaweeds), which can cause major ecological impacts such as the displacement of indigenous species, habitat alteration, and oxygen depletion in bottom waters.
Few would argue that the number of toxic blooms, economic losses from them, the types of resources affected, and the number of toxins and toxic species have all increased dramatically in recent years throughout the world. Disagreement only arises with respect to the reasons for this expansion. The maps in this section depict the incidence of HABs in the U.S. and worldwide.  These maps were created using data collected annually for the Harmful Algae Event Database (HAEDAT) maintained by the ICES Science and Communications Center in Vigo, Spain. Each "Event" noted on the map is considered to be something that constituted a quarantine, closure or management decision where toxicity was detected exceeding regulatory limits.
***Note that the known distribution surely reflects the degree of sampling and monitoring effort, and thus some regions may be over- or under-represented. Continued efforts to better detect and identify taxa and toxins will aid in a more fuller characterization of HABs in the U.S. and around the world.