Keeping an Eye on Algal Blooms and Hypoxia

Fish kill in the Chautauqua National Wildlife Refuge due to a harmful algal bloom.

Fish kill in the Chautauqua National Wildlife Refuge due to a harmful algal bloom.

High resolution (Credit: NOAA)

Dead fish or dolphins. Shellfish beds closed to harvesting. Coughing beachgoers with burning throats and eyes. Discolored water. Decaying algae piled along the beach. The cause? A harmful algal bloom (HAB) could be the culprit.

While algae are beneficial because they provide the main source of energy that sustains marine life, an abundance of certain species – the ‘harmful algae’ – can harm humans, animals, or the environment. Hypoxia is a separate, but sometimes related, issue caused when excess organic matter, often from algal blooms, decomposes and reduces oxygen dissolved in the water. Most organisms avoid or die in waters with low oxygen, thus the common term, “dead zone.”

HABs and hypoxia are harming an increasing number of the world’s ecosystems and coastal communities. In the U.S., every coastal state has reported recurring blooms and over half of our nation’s estuaries experience hypoxia. Effects of HABs include massive fish kills, devastation of critical coastal habitats, vital shellfish resource loss, illness and death of protected marine species, and threats to human health.  

Just one HAB event can result in millions of dollars in losses to local coastal economies.  

What Is NOAA Doing to Help?

NOAA is working to monitor, understand, and predict HABs and hypoxia and their effects. As a result, strategies can be developed to predict events, minimize effects, and potentially prevent their occurrence. 

Image of red tide taken from the NOAA vessel Ron Brown, April 5, 2001.

Image of red tide in Gulf of Mexico taken from the NOAA vessel Ron Brown in 2001.

High resolution (Credit: NOAA)

Monitoring and Predicting HABs: New England Example

In New England, Alexandrium, an alga also known as New England Red Tide, blooms each year, resulting in shellfish harvesting closures. Alexandrium produces a potent toxin that accumulates in shellfish and can cause illness in humans who eat contaminated shellfish.

This year, scientists at Woods Hole Oceanographic Institution are forecasting a larger than normal bloom year in New England. This year’s bloom could be comparable to the historic bloom of 2005 that resulted in an estimated impact of $18 million to the commercial shellfish industry in Massachusetts.  

This forecast is a product of a complex model developed with NOAA’s National Centers for Coastal Ocean Science (NCCOS) support. The forecast is updated weekly and predicts Alexandrium abundance and the path of the bloom, providing critical information to alert marine resource managers and help focus monitoring strategies. 

Predictions such as these minimize the economic effects of shellfish closures while safeguarding human health.

Monitoring and Predicting Hypoxia: Gulf of Mexico Example

The northern Gulf of Mexico contains almost half of the nation's coastal wetlands and supports commercial and recreational fisheries that generate $2.8 billion annually. This region has a large area of bottom water hypoxia, known as the “Dead Zone” that recurs every summer.

NOAA-sponsored research has documented the size of the dead zone in the Gulf of Mexico since 1985 and, since 2003, has forecasted the annual size based on nutrient inputs from the Mississippi River. This research is being used by a federal and state task force charged with addressing the recurring dead zone. NOAA logo.