Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

For the purposes of this analysis, harmful algal blooms (HABs) are defined as (1) an increase in the abundance of species that are known to produce toxins harmful to marine animals or humans (see Table 2); (2) the occurrence of lesions or mass mortalities of marine animals caused by HAB species; and (3) the occurrence of human pathologies caused by HAB species. A single event counts only once toward the relative intensity scale, even if it produces multiple impacts (e.g., an increase in the abundance of a HAB species that causes mass mortalities and an increased human health risk will be counted as a single event).

There are approximately 5000 species of microalgae in the world. Of these, about 100 are toxic. The scientific community refers to the phenomenon that cause these events as HABs, recognizing that HAB species represent a broad spectrum of taxa (e.g., dinoflagellates, diatoms, cyanobacteria) and trophic levels (e.g., autotrophic, heterotrophic, mixotrophic) and that many HAB species cause problems at low cell densities (i.e., a visible bloom is not necessarily required for a HAB event to occur). A second group of problematic algal blooms is recognized: those that cause problems such as oxygen depletion, habitat loss, starvation, or respiratory or reproductive failure in marine animals by virtue of their high abundance or biomass. These issues are addressed to some extent in other indicators.

Although definitive scientific evidence is lacking, HAB events appear to be increasing in number, extent, and severity (see National Assessment of Harmful Algal Blooms in US Waters, http://www.habhrca.noaa.gov/FinalHABreport.pdf). Rapid increases in the number of people living, working, and playing in the coastal zone have increased the input of nutrients to coastal waters, and HAB events may be occurring more frequently as a consequence. In addition, increases in shipping (and the inadvertent transport of non-native species of algae in ballast water) and the transport of shellfish between regions and continents may be increasing the frequency of HAB events by introducing new HAB species to U.S. coastal waters, or moving them to new locations within the United States. A growing human population also increases the demand for food from coastal waters in the form of wild and cultured fish and shellfish. The aquaculture industry is threatened by HAB events and may contribute to their increase.

The Data Gap

Most harmful algal events, such as fish kills, are typically identified after the event occurred or when it is well under way. Systematic monitoring programs that (1) quantify the abundance of harmful algal species, (2) quantify the concentrations of biotoxins or establish unequivocal causal relations between HAB species and mortality events, or (3) quantify increases in human health risks are rare. Consequently, the data required to calculate this index on regional or national scales do not exist.

Although efforts to monitor and report these events are increasing nationwide, there is no standard measure of HABs. This is largely because of the heterogeneous nature of HABs (in terms of taxonomy, nutrition, the conditions under which they become toxic, the kinds of toxins produced, and their effects) and the fact that some species cause problems when they bloom while others cause problems at low cell densities.

State, federal, and academic programs collect most existing data, such as those in the database maintained by the Florida Marine Research Institute, for specific purposes (e.g., research or mitigation) or for specific locations (e.g., the west coast of Florida) where HABs have caused problems in the past. Thus, there is little consistency among programs, and there is no mechanism in place to establish regional or national databases. Both the National Oceanographic and Atmospheric Administration (NOAA; http://www.nodc.noaa.gov/col/projects/habs/index.html) and the Environmental Protection Agency (EPA; http://es.epa.gov/ncer/rfa/02ecohab.html) have initiated efforts to address these problems, and the U.S. Global Ocean Observation System Program, in collaboration with the Southern Association of Marine Laboratories and the Gulf of Mexico Program, is developing a prototype system for the northern Gulf of Mexico (http://www.hpl.umces.edu/projects/HABSOS.pdf).

In addition, the Harmful Algal Bloom and Hypoxia Research and Control Act was enacted in 1998 (PL 105-383) in response to concerns that HABs and related environmental events (e.g., hypoxia, fish kills) are increasingly a threat to human and coastal ecosystem health. The act called for the establishment of an interagency task force on HABs and hypoxia; a national assessment of HABs and hypoxia; and an assessment plan for the Gulf of Mexico. A federal interagency task force released the National Assessment of Harmful Algal Blooms in US Waters in October 2000 (http://www.habhrca.noaa.gov/FinalHABreport.pdf).