Phytoplankton: The Tiny Algae That Feed the Sea, and Sometimes Poison It

Much of the food in the sea starts as something too small to see. Phytoplankton are microscopic marine algae, and in a balanced ecosystem they sit at the base of several aquatic food webs, feeding shrimp, snails, jellyfish and a wide range of other sea creatures. The same organisms, given too much to eat themselves, can turn into one of the ocean's hazards.

Phytoplankton, the base of several aquatic food webs. Credit: NOAA.

Built like land plants

Phytoplankton, also called microalgae, live much as land plants do. They contain chlorophyll and need sunlight to live and grow, which is why most of them are buoyant and drift in the upper layer of the ocean, where light reaches. They also need inorganic nutrients — nitrates, phosphates and sulfur — which they turn into proteins, fats and carbohydrates.

Two kinds, two ways of getting around

The two main classes of phytoplankton differ in how they are built and how they move:

When the base of the food web turns toxic

Phytoplankton become a problem when they have too many nutrients. Then they can grow out of control and form harmful algal blooms, or HABs. Some of these blooms produce extremely toxic compounds that harm fish, shellfish, mammals, birds and even people.

The National Centers for Coastal Ocean Science research these blooms extensively. Scientists use a range of technologies to predict where and when a HAB is likely to form and how it will affect the area, and pass that on to coastal authorities so they can respond in the way that does the least harm.

Sources

Based on "What are phytoplankton?" from NOAA's National Ocean Service, a work of the United States government in the public domain.