Scientists Work to Predict and Prevent Algae Blooms

An algal bloom, also known as a red tide, has converted the ocean's surf to a red color

Harmful algal blooms are dangerous, producing toxins that can kill marine organisms, taint shellfish, cause skin irritations, and even foul the air


Flickr User AJC1

Algae, like all organisms, normally grow in balance with their ecosystems, limited by the amount of nutrients in the water. But sometimes, certain species of algae reproduce so rapidly that they cause damage. In the ocean, microscopic forms of algae can "bloom" into dense patches near the surface, often referred to as "red tides." Some of these harmful algal blooms (HABs) are dangerous, producing toxins that can kill marine organisms, taint shellfish, cause skin irritations, and even foul the air.

HABs occur worldwide. They seem to be increasing in size, intensity, and persistence—possibly due to nutrient-rich runoff from land or a warming climate. In the U.S., HABs have devastated Long Island's scallop fishery and caused seasonal closures of other shellfish beds along the Atlantic, Gulf of Mexico, and Pacific coasts. Scientists suspect the blooms may also have contributed to the deaths of hundreds of manatees, sea lions, and other marine mammals. Airborne toxins from the blooms have made vacationers and coastal residents sick, and damage from HABs costs coastal economies tens of millions of dollars each year.

Sea lions have been getting very sick, and the Marine Mammal Center in California has traced one of the causes to harmful algal blooms that pose a risk to human health as well.

These algae, known as dinoflagellates, may become so dense that they overgrow corals, clog harbors, or block sunlight to seagrass and marine critters. Larger forms of algae (we know them as seaweed) can also grow out of control, especially on reefs with few algae-eating animals and in areas with high levels of runoff or sewage pollution.

Scientists at the National Oceanographic and Atmospheric Administration (NOAA) are working with universities from the Gulf of Maine to the Puget Sound to develop systems that track and predict harmful algal blooms. In Massachusetts, scientists are experimenting with a sensor that can identify three types of dangerous microscopic algae by their genetic material and offer an early warning when they are detected in the water. In the Gulf of Mexico, NOAA's HAB Forecasting System pulls together satellite imagery, information about water conditions gathered by weather buoys, and observations from scientists in the field to map blooms and predict how they will spread.

Knowing when and where HABs are likely to occur can help scientists and public officials minimize harm to people and marine life. And learning more about the causes of the blooms may ultimately help us prevent them. To learn more about how you can help prevent algal blooms and "dead zones", visit the Ocean Portal's Find Your Blue page.


Dinoflagellates are major producers of oxygen in the ocean (and freshwater). But some species can grow out of control, causing a red tide.


© 2004 Smithsonian Institution