Harmful Algal Blooms: Simple Plants
With Toxic Implications

Ranging from microscopic, single-celled organisms to large seaweeds, algae are simple plants that form the base of food webs. Sometimes, however, their roles are much more sinister. A small percentage of algal species produce toxins that can kill fish, mammals, and birds, and may cause human illness. Other algae are nontoxic, but clog the gills of fish and invertebrates or smother corals and submerged aquatic vegetation.  Others discolor water, form huge, smelly piles on beaches, or cause drinking water and fish to taste bad.


This deep red harmful algae, called Lingulodinium polyedrum, often produces brightly colored water discoloration. It has been associated with fish and shellfish mortality events, but its threat to human health is still being evaluated. (photo credit: Kai Schumann, California Department of Public Health volunteer)

HAB Impacts Are Far Reaching

Harmful algal bloom (HAB) events can be very bad for us. People who eat shellfish from waters experiencing toxic blooms can become very ill and can even die.

Does that mean that the seafood you eat may be unsafe? Not at all. Rigorous state shellfish monitoring programs ensure that legally harvested seafood is safe for human consumption.

HABs also have economic and cultural implications, especially in coastal communities dependent on harvesting seafood and tourism. They frequently disrupt the commercial, recreational and subsistence seafood harvesting and cause some to cancel beach vacations.

As a result HABs cost coastal communities a substantial amount. Coastal HAB events have been estimated to result in economic impacts in the United States of at least $82 million each year.

These impacts stress the importance of understanding HABs and developing tools to mitigate their impacts and ultimately to control or even prevent them.

Lake Erie HAB

Harmful algal blooms are not just a problem along the coasts. The harmful algae seen here along the shores of Lake Erie in Ohio is called Microcystis. Microcystis blooms are increasing in frequency and duration in the Great Lakes.

A Legislative Mandate

In December 2004, the Harmful Algal Bloom and Hypoxia Amendments Act of 2004 (Public Law 108-456) was signed into law.

This Act, originally passed in 1998, reaffirms and expands the mandate for NOAA to advance scientific understanding and detection, monitoring, assessment, and prediction of harmful algal blooms (HABs) and hypoxia (low oxygen).

The Act calls for development of programs to research methods of prevention, control, and mitigation of HABs and establishes an interagency task force to follow progress on these issues.

Tools and technologies being developed under the Act are helping coastal managers lessen or prevent impacts on human health and coastal resources.

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Understanding HABs Where They Occur

Although all coastal states experience harmful algal blooms, different organisms live in different places and cause different problems. Other factors, such as the structure of the coast, runoff, oceanography, and other organisms in the water, can also change the scope and severity of HAB impacts.

To address these differences, NOS takes a regional approach in developing strategies for HAB management.  By developing specific tools and information for areas of the country, including the Gulf of Mexico, Great Lakes, Northeast, Pacific Coast, Mid-Atlantic/Southeast, and Caribbean/Pacific Islands, NOS is able to advance management capabilities in dealing with all major HAB threats.

HAB map of US

Approximate areas of the U.S. coast affected by various HAB poisoning syndromes and other impacts. (credit: U.S. National Office for Harmful Algal Blooms, Woods Hole Oceanographic Institution)

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Sediment Core sampling

A University of Washington researcher collects sediment cores in Puget Sound to examine for seed-like cysts of the toxic dinoflagellate, Alexandrium catenella. A. catenella produces a neurotoxin that accumulates in shellfish. Cysts are deposited in the fall and lie dormant on the bottom. They hatch in the spring when temperatures of bottom water increase. Warming of bottom waters associated with climate change may allow cysts to hatch earlier, thus increasing the length of blooms of toxic A. catenella. (credit: Dr. Cheryl Greengrove, University of Washington Tacoma)

HABs and Climate Change

Climate is always changing. Because the growth, toxicity, and distribution of harmful algal bloom (HAB) species are all tied to the environment, changes in climate can change the occurrence, severity, and impacts of HAB events.

Climate change will largely manifest as regional changes, which closely aligns with NOS’s regional approach to its HAB research. This knowledge will be critical to developing strategies for management of HABs in already vulnerable coastal and marine areas into the future.

To understand how future climate changes may impact HABs, NOAA supports a wide variety of research. The Center for Sponsored Coastal Ocean Research, for example, supports projects addressing the impacts of climate change on HABs in estuarine, coastal, and Great Lakes ecosystems.

NOAA's Oceans and Human Health Initiative (OHHI) also supports HAB research related to climate change. At OHHI's West Coast Center, researchers are studying human health impacts related to environmental variability and climate change — factors that impact the severity, transport, concentration, and dispersion of HABs.

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Sediment Core sampling

Researchers onboard the Woods Hole Oceanographic Institution vessel R/V Tioga conducting a survey to map the distribution and abundance of toxic Alexandrium fundyense in the Gulf of Maine. (credit: Woods Hole Oceanographic Institute)

Research to Combat HABs

The National Centers for Coastal Ocean Science (NCCOS) is leading NOAA efforts to research and understand harmful algal blooms (HABs), to develop tools to combat these toxic tides.

For example, NCCOS’s Ecology and Oceanography of Harmful Algal Blooms Research Program is producing new methods to detect HABs and their toxins, to understand HAB dynamics, to develop HAB forecasts, and to predict and reduce impacts on people and ecosystems.

The NOAA Monitoring and Event Response for Harmful Algal Blooms Research Program  is expanding efforts to monitor waters and shellfish, to help more coastal communities know when they are at risk and how to respond.

While most HAB programs in NOAA fall within NCCOS, HAB research, management, and response efforts span across many offices. NOAA's Oceans & Human Health Initiative, for example, supports a wide range of HAB research with a focus on public health.

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Warning Sign

A warning sign located on Marrowstone Island, Washington.

Preventing HABs Before They Happen

The Prevention, Control, and Mitigation of Harmful Algal Blooms (PCM HAB) Research Program transitions promising prevention, control, and mitigation technologies and strategies to coastal managers.

PCM HAB also assesses the social and economic costs of HAB events and the costs and benefits of mitigation strategies, to help managers develop cost-effective management strategies.

The transfer of such technology can yield many benefits for the public, including healthier fisheries and ecosystems, fewer impacts of blooms on humans and the environment, and reductions in nuisance or harmful accumulation of algae. 

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HAB bulletin

NOAA's Harmful Algal Bloom Operational Forecast System (HAB-OFS) provides information on the location, extent, and the potential for development or movement of harmful algal blooms in the Gulf of Mexico. The forecast system relies on satellite imagery, field observations, models, public health reports and buoy data to provide the large spatial scale and high frequency of observations required to assess and predict bloom conditions, location and movements.

Identifying and Monitoring HABs

Finding HABs and measuring their toxins isn't easy.  The methods that are traditionally used are very time consuming and require specialized labs.  For example, HAB cells are often collected on a boat, preserved, and counted under a microscope, so the data are not available for several days.  Faster, cheaper, and better methods of cell and toxin detection are needed.

Scientists, such as those at the Center for Coastal Monitoring and Assessment, often use satellites to collect data on ocean color in order to determine the amount of live biomass (e.g. phytoplankton) in the ocean and to identify and track algal blooms and track plumes. Scientists combine this satellite data with data collected by research vessels to gain a better understanding of the occurrence, trajectory, and potential landfall of a bloom. This information can then be passed on to coastal managers and state agencies, so that strategies to deal with an impending bloom can be put in to place.  The problem with this method, though, is that it only works with some types of blooms.

That's why researchers throughout NOAA are working on many different ways to detect and monitor algal blooms and their toxins. One example is the Phytoplankton Monitoring Network. Run by the Center for Coastal Environmental Health and Biomolecular Research, this program trains volunteers

Domoic acid test kit in use

Domoic acid test kits are saving West Coast coastal communities and fishers effort and time in assuring the safety and vitality of a coastal resource they depend on, both for food and for tourism income.

around the nation to gather water samples and identify different types of phytoplankton in coastal waters. Another technique now in development involves the use of underwater sensors on buoys or attached to unmanned underwater vehicles.  

NOAA scientists have recently developed a test kit for domoic acid, a potent neurotoxin sometimes found in shellfish.  The test kit is designed to be easy to use and requires no specialized equipment. NOAA also funded development of a new test for brevetoxin, the Florida red tide toxin, that is now used routinely to screen commercial shellfish and in marine forensic investigations to help determine if red tide is linked to deaths of dolphins, manatees and other marine animals. Check out some of the links below to learn about the many ways that HABS are detected and monitored.

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gulf of Maine cyst map

Map of Alexandrium fundyense cyst distribution on the Gulf of Maine in 2009. Cyst maps from sediments collected in the fall are used to predict the severity of the A. fundyense bloom the next spring and summer. (credit: Woods Hole Oceanographic Institute)

Forecasting HABs

Advance warning of harmful algal blooms (HABs) increases the options for managing these events. First it is necessary to understand when and where blooms occur and how they respond to changing environmental conditions, through research programs such as NOAA's Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) Program. Armed with sufficient information, it is then possible to predict blooms.

NOAA’s HAB Operational Forecast System, run out of the Center for Operational Oceanographic Products and Services and supported by the Center for Coastal Monitoring and Assessment, uses satellite imagery, field observations, and buoy data to determine the location, extent, and potential for development or movement of HABs in the Gulf of Mexico.

Conditions, including information on potential or confirmed harmful bloom events, chlorophyll levels, and forecasted winds, are posted as HAB Bulletins online twice a week during the bloom season. The bulletins also provide forecasts for potential human impacts associated with confirmed harmful blooms, bloom sizes, movement, intensification, and the potential for bloom formation.

Similar forecasts are now in developmental stages for the Great Lakes, the Gulf of Maine, and other 'HAB hotspots' around the country.

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dead dolphin

107 bottlenose dolphins stranded dead along the Florida Panhandle in 2004. Hundreds of dead fish and marine invertebrates were also discovered in the area. Read the NOAA report (pdf, 1.8MB) on this incident.

HAB Response

When harmful algal bloom (HAB) events occur, NOAA is there to help coastal states.

The Center for Sponsored Coastal Ocean Research HAB Response Event Program, for example, provides immediate assistance for managing events by offering technology and expertise, providing supplemental financial support for investigating events, and ensuring events are properly documented.

The Program assesses human health risks, identifies causes of marine mammal mortalities, offers training opportunities for managers, and establishes baseline conditions for new or re-emerging HABs.

The HAB Analytical Response Team, part of the Marine Biotoxins Program, provides scientific guidance and identification of harmful algae and their toxins during suspected HABs, during marine animal mortality events, and during human poisonings.

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More Information

The following is a consolidated list of all external links referenced in this article.

HAB impacts

Legislative Mandate

Understanding HABs Where They Occur

HABS and Climate Change

Research to Combat HABs

Preventing HABs Before They Happen

Identifying and Monitoring HABs

Forecasting HABs

HAB Response