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Harmful Algal Blooms

Tiny Plants with a Toxic Punch

What is a Harmful Algal Bloom (HAB)?

This deep red harmful algae, called Lingulodinium polyedrum, often produces brightly colored water discoloration.

This deep red harmful algae, called Lingulodinium polyedrum, is a type of HAB that 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. Credit: Kai Schumann, California Department of Public Health volunteer

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 more sinister. Under the right conditions, algae may grow out of control — and a few of these "blooms" produce toxins that can kill fish, mammals, and birds, and may cause human illness or even death in extreme cases. Other algae are nontoxic, but eat up all of the oxygen in the water as they decay, clog the gills of fish and invertebrates, or smother corals and submerged aquatic vegetation. Still others discolor water, form huge, smelly piles on beaches, or contaminate drinking water. Collectively, these events are called harmful algal blooms, or HABs.

Every U.S. coastal and Great Lakes state experiences HABs. These blooms are a national concern because they affect not only the health of people and marine ecosystems, but also the "health" of our economy — especially coastal communities dependent on the income of jobs generated through fishing and tourism. With climate change and increasing nutrient pollution potentially causing HABs to occur more often and in locations not previously affected, it's important for us to learn as much as we can about how and why they form and where they are, so that we can reduce their harmful effects.

NOAA is on the forefront of HAB research to better understand how and why these blooms form, and to improve detection and forecasting of these seasonal events. One of our top goals is to provide communities with advance warning so they can adequately plan for and deal with the adverse environmental, economic, and health effects associated with HABs.

Why do HABs happen?

Harmful algal blooms, or HABs, are a growing problem in every U.S. coastal and Great Lakes state. While we can't prevent these blooms, we can be better prepared. NOAA leads many research efforts to help coastal communities counter the environmental and health effects associated with these events.

Harmful algal blooms, or HABs, are a growing problem in every U.S. coastal and Great Lakes state. While we can't prevent these blooms, we can be better prepared. NOAA leads many research efforts to help coastal communities counter the environmental and health effects associated with these events.

While we know of many factors that contribute to HABs, how these factors come together to create a "bloom" of algae is not well understood. HABs occur naturally, but human activities that disturb ecosystems seem to play a role in their more frequent occurrence and intensity. Increased nutrient loadings and pollution, food web alterations, introduced species, water flow modifications, and climate change all play a role.

Coastal HAB events have been estimated to result in economic impacts in the United States of at least $82 million each year.

Studies indicate that many algal species flourish when wind and water currents are favorable. In other cases, HABs may be linked to "overfeeding." This occurs when nutrients (mainly phosphorus and nitrogen) from sources such as lawns and agriculture flow into bays, rivers, and the sea, and build up at a rate that "overfeeds" the algae that exist normally in the environment. Some HABs appear in the aftermath of natural phenomena like sluggish water circulation, unusually high water temperatures, and extreme weather events like hurricanes, floods, and drought.

Although all coastal states experience HABs, 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, NOAA takes a regional approach in developing strategies for HAB management.  By developing specific tools and information for specific areas — the Gulf of Mexico, Great Lakes, Northeast, Pacific Coast, Mid-Atlantic/Southeast, and Caribbean/Pacific Islands — NOAA is able to advance regional and local management capabilities to deal with major HAB threats.

Where do HABs happen?

 A close-up of Pseudo-nitzchia, a common a common type of phytoplankton. Sometimes, Pseudo-nitzchia blooms may produce domoic acid, a neurotoxin that can cause amnesiac shellfish poisoning

A close-up of Pseudo-nitzchia, a common a common type of phytoplankton. Sometimes, Pseudo-nitzchia blooms may produce domoic acid, a neurotoxin that can cause amnesiac shellfish poisoning.

Finding HABs and measuring their toxins is a complex task. While traditional methods are time-consuming and require specialized labs, NOAA researchers are working on faster, cheaper, and better ways to detect and monitor algal blooms and their toxins. Here are three examples.

In 2015, NOAA joined forces with NASA, the U.S. Environmental Protection Agency, and U.S. Geological Survey to transform satellite data designed to probe ocean biology into information that will help protect the American public from harmful freshwater algal blooms. The effort is designed to be an early warning system for toxic and nuisance algal blooms in freshwater systems by using satellites that can gather color data from freshwater bodies during scans of the Earth. Based off this information, state and local agencies can provide the public with public health advisories. In addition, the project will improve the understanding of the environmental causes and health effects of these cyanobacteria and phytoplankton blooms in the United States.

Another technique now in development involves the use of underwater sensors on buoys or attached to unmanned underwater vehicles.  For example, NOAA is funding the development of a network of automated submersible microscopes called "Imaging Flow Cytobots" for monitoring and early warning of HABs.  Every 20 minutes, this device sips the water.  As the water stream passes a laser, a picture is taken of any cells that contain the algal pigment, chlorophyll.  A computer analyzes the image to identify the algal cell, counts any HAB cells, and sends a message to a public health manager when the numbers of HAB cells exceed a threshold.

The Phytoplankton Monitoring Network is another initiative that is making a difference. This program trains volunteers around the nation to gather water samples and identify potentially harmful  types of phytoplankton (one-celled organisms) in coastal waters.

How we forecast HABs.

Public warning signs appear in areas that have been closed due to high levels of toxin in shellfish.

Public warning signs appear in areas that have been closed due to high levels of toxin in shellfish.

Scientists forecast a harmful algal bloom just as they forecast a hurricane. Like a weather forecast, a HAB forecast provides local and state officials with advance warning that allows them to test potentially affected shellfish beds more precisely and for shorter periods of time and, if necessary, post advisories in coastal areas where there is a direct health risk.

Today, NOAA's HAB Operational Forecast System encompasses Florida and Texas — a region that routinely experiences HAB outbreaks. This forecast system identifies whether or not a bloom of algae is likely to contain a toxic species, where it is, how big it is, where it's headed, and if it could become more severe in the near future.

In the Gulf of Mexico, especially the west coast of Florida and the Texas coast, the most frequent cause of HABs is Karenia brevis. The toxin from this HAB becomes airborne when waves break on the beach, which causes severe respiratory irritation. HAB forecasts in this region rely on satellite imagery, field observations, models, public health reports, and buoy data. Using all this information, forecasters can create a public HAB Bulletin that predicts the likelihood of respiratory irritation to people in the area in the coming days. HAB Bulletins are posted twice a week during the bloom season.

Similar forecasts are now being demonstrated in Lake Erie, Puget Sound, Chesapeake Bay, the Gulf of Maine, and other HAB "hotspots."