Not All Algal Blooms Are Harmful — Some Feed the Whole Ocean

"Algal bloom" sounds like bad news, and sometimes it is. But of the thousands of species of algae, most are beneficial, and only a few produce toxins or cause other harm. Some blooms are good for the ocean.

When a bloom is harmful

Harmful algal blooms are blooms of algae species that hurt people, marine and freshwater environments, and coastal economies. They happen when phytoplankton — tiny microscopic plants — multiply quickly in large numbers and have toxic or harmful effects on people, fish, shellfish, marine mammals and birds.

Harm without poison

A bloom does not need to produce toxins to damage the environment. It can:

• use up the oxygen in the water, creating anoxic conditions
• block light from organisms deeper in the water column
• clog or damage the gills of fish

When a bloom is good

Other blooms are beneficial. Phytoplankton sit at the base of the marine food chain, so all other life in the ocean depends on them. Blooms can also be a useful signal of environmental change — not only in the water, but on land as well.

Predicting the harmful ones

Scientists work to predict how harmful algal blooms will spread; NOAA's Ocean Today explains how in a short video.

Sources

Based on "Are all algal blooms harmful?" from NOAA's National Ocean Service, a work of the United States government in the public domain.