About Harmful Algal Blooms

Most algae are aquatic plants that lack stems, roots and leaves, though some can live on land in moist environments. They are a key part of most water ecosystems and the majority of algae are not harmful. However, when certain types of algae grow quickly, they form visible patches and emit toxins that can harm plants, animals and negatively impact the ecosystem.

Facts

• Harmful algal blooms grow quickly, depleting oxygen in the water and blocking sunlight that many aquatic plants and animals need. The harmful algal blooms can be green, brown or even reddish orange. When these events occur in the sea, they are commonly called red tides.

  Some harmful algal blooms release toxins as they grow that can harm other species. Harmful algal blooms occur in both fresh and marine environments and their frequency appears to be increasing, according to the Centers for Disease Control and Prevention (CDC).

Types

• The Woods Hole Oceanic Institute estimates that only a few dozen of the thousands of types of algae cause harmful algal blooms. Three types of algae are associated with public health dangers. Cyanobacteria, which are blue-green, produce toxins that taint both drinking water and lakes. Swimming in or drinking water tainted with cyanobacteria can cause stomach flu, skin irritations and even liver damage.

  Harmful marine algae produce red tides containing toxins that can harm or kill fish and other marine animals. If humans eat contaminated fish, they may have neurologic symptoms like tingling fingers and toes or stomach flu. If toxins are inhaled, some people suffer asthma attacks.

  Pfiesteria piscicida is a type of algae that lives in estuaries and has been found where there are large quantities of dead fish. While the CDC has no evidence that this algae harms people, there have been reports of exposure causing headaches, rashes and skin irritations in humans.

Causes

• The causes of harmful algal blooms are not well understood. Algae grow quickly when conditions like light, temperature and salinity favor development. Sometimes it accumulates because of ocean currents. In other cases, it is overfed by nutrients in run-off from lawns and farmlands, according to the National Ocean Service. Some harmful algal blooms result from weather events like hurricanes, floods and unusually high water temperatures.

Consequences

• The most significant consequences are associated with marine harmful algal blooms. The U.S. Environmental Protection Agency notes that recently there has been a noticeable increase in harmful algal bloom problems. These include human illness and death, contaminated seafood, extensive fish kills and the death or marine birds and mammals.

  The Center for Sponsored Coastal Ocean Research (CSCOR) estimates that the economic impact from harmful algal blooms costs the U.S. roughly $82 million each year, mainly in the public health and commercial fishing sectors. This estimate is probably low because it does not count the expenses of unreported illness, lowered property values, lost seafood sales and lost revenue from small fisheries.

Management

• The National Oceanic and Atmospheric Administration (NOAA) is studying ways to manage, control and even prevent harmful algal blooms. Its major goal is to predict areas that may experience harmful algal blooms. Using satellite sensors and field observation from research vessels, NOAA recently produced a remote sensing tool to predict and manage harmful algal blooms in the Gulf of Mexico. In addition, it regularly distributes bulletins about developing blooms and the extent of existing harmful algal blooms to lessen their impact.