Extracted from:

Donald F. Boesch, Donald A. Anderson, Rita A. Horner, Sandra E. Shumway,Patricia A. Tester and Terry E. Whitledge. 1997. Harmful Algal Blooms in Coastal Waters: Options for Prevention, Control and Mitigation. NOAA Coastal Ocean Program, Decision Analysis Series No. 10, Special Joint Report with the National Fish and Wildlife Foundation, February 1997.

Site developer's note: genus and species names of algae are indicated in red, rather than standard underlining (not a webpage option unless a link...) or italics, in order to make the names easier to find and read.

What are Harmful Algal Blooms?

The term "harmful algal blooms" (shortened for convenience here to HABs) has been used by the scientific community to describe a diverse array of blooms of both microscopic and macroscopic marine algae which produce: toxic effects on humans and other organisms; physical impairment of fish and shellfish; nuisance conditions from odors and discoloration of waters or habitats. Although the use of the terms "bloom" or "red tide" conjure up an image of algal populations so dense as to be visible, this is not always the case with HABs. Concentrations of only a few cells per liter of some microalgae may produce harmful toxic effects.

This assessment focused on blooms of microscopic algae occurring in the coastal waters of the United States which produce toxic effects and impairment of fish and shellfish production, either directly or indirectly, via degradation of habitats. The focus was on a relatively few species of microscopic marine algae which cause the following:

Blooms producing neurotoxic shellfish poisoning (NSP). These are caused by the dinoflagellate Gymnodinium breve and occur along the coasts of the Gulf of Mexico, and rarely, the southeast Atlantic coast.

Blooms causing paralytic shellfish poisoning (PSP). Various species of the dinoflagellate genus Alexandrium are responsible for PSP in New England, northern California, the Pacific Northwest and Alaska.

"Brown tide" blooms (BTB) caused by very small golden brown algae. These seem to be a recent occurrence in relatively enclosed waters of southern New England, particularly Long Island (New York) and Texas. Aureococcus anophagefferens is responsible for similar species, Aureoumbra lagunesis, blooms in Texas bays and lagoons.

Blooms of various species of the diatom genus Pseudo-nitzschia produce domoic acid that causes amnesic shellfish poisoning (ASP). Domoic acid poisoning may also be experienced by humans, mammals, and birds from consumption of fish and other invertebrates. Toxin-producing species of Pseudo-nitzschia occur on the northwest, east and Gulf coasts, but no confirmed cases of ASP have occurred in humans in the United States.

Blooms which which do not cause illness in humans but result in catastrophic losses of cultured and wild fish, particularly in the Pacific Northwest. Such blooms are caused both by the raphidophyte flagellate Heterosigma akashiwo and by a few species of the diatom genus Chaetoceros, which clog fish gills.

UNIVERSITY OF MARYLAND College of Ag & Natural Resources Department of Veterinary Medicine Aquatic Pathobiology Center