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Magnified HAB cells (Alexandrium). Photo

credit: WHOI

You are here: Home › Stressors › Extreme Events › Harmful Algal Blooms

Overview of Harmful Algal Blooms

Click Here for information about the West Coast HAB Summit

Why is this issue important?

A small percentage of algal species cause harm to humans and the environment through toxin production or

excessive growth—these are the harmful algae and they include both microalgae (microscopic , single celled

organisms) and macroalgae (seaweeds). Some harmful algae produce potent toxins which cause illness or

death in humans and marine organisms—fish, seabirds, manatees, sea lions, turtles, and dolphins are some

commonly affected animals. Other types of harmful algae are nontoxic to humans but cause harm to fish and

invertebrates by damaging or clogging their gills or by forming such large blooms that the death and

subsequent decay of the algae lead to hypoxia (oxygen depletion) in the bottom waters of marine

environments. Dense blooms can also block sunlight for beneficial algae and seagrasses. 

HABs can have major negative impacts on local economies, and a recent conservative assessment estimates

that HABs occurring in marine waters alone have an average annual impact of $82 million dollars in the U.S.

All U.S. coastal states have experienced HABs over the last

decade, and new species have emerged in some locations that

were not previously known to have problems. HABs occur

naturally, but human activities that disturb ecosystems in the form

of increased nutrient loadings and pollution, food web alterations,

introduced species, and water flow modifications have been linked

to the increased occurrence of some HABs.

■ Economic Impacts of HABs

■ Human Dimensions of HABs

How are we addressing this issue?

NOAA’s goal is to provide tools to prevent, control, or mitigate the occurrence of HABs and their impacts. In

the 10 years following the passage of the original Harmful Algal Bloom and Hypoxia Research and Control Act

(HABHRCA), CSCOR HAB Programs have made significant advances that have improved HAB management. 

More accurate and efficient tools for detecting cells and toxins, early warning of toxic blooms, better

predictions of when and where the blooms will move, and partnerships developed that allow for more effective

response are just a few examples of how CSCOR-supported HAB research has benefited society. Because the

challenges for managing HABs differ among regions of the country, CSCOR maintains a regional approach to its

research that will continue to advance management capabilities in dealing with all the Nation’s major HAB

threats.

• Click here for Information about CSCOR's Regional HAB Research

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