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Algae, like all organisms, normally grow in natural balance with their ecosystems. 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.

shellfish closure sign
This sign warning people that shellfish in this bay contain high levels of toxins was posted in 2005 during a massive red tide in New England. Image courtesy: Judy Kleindinst/WHOI

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.

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. These non-toxic algae may become so dense that they overgrow corals, clog harbors, or block sunlight to seagrass and marine critters.

red tide
An alarming "red tide" off the coast of New Zealand. While this species (called Noctiluca scintillans) does not produce a toxin, it has been associated with fish die-offs. Image courtesy: Miriam Godfrey

Scientists at 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. Click here to learn how you can help prevent algal blooms and "dead zones" by limiting the amount of fertilizer and chemicals your family uses.

Related Links...

Smithsonian Algae Research Page

Wood Hole Oceanographic Institute Harmful Algae Page

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