Phytoplankton are microscopic marine plants

scanning electron microscope image of phytoplankton

Phytoplankton, also known as microalgae, are similar to land-based plants in that they contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean, where sunlight penetrates the water. Phytoplankton also require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert into proteins, fats, and carbohydrates.

In a balanced ecosystem, phytoplankton provide food for a wide range of sea creatures including krill, shrimp, snails, and jellyfish, that are in turn food for larger animals like sea turtles, fish and whales. However, under certain environmental conditions, such as the introduction of too many nutrients from land based sources of pollution, phytoplankton may grow out of control and form blooms.

These blooms can be problematic because the excess algae can block out sunlight, which is bad for plants like seagrasses that need sunlight to make food. Zooxanthallae, or symbiotic algae that live in the tissue of coral and supply coral with food, can also be impacted by algal blooms. Excess algae can also smother other critters living on the ocean floor.

When blooms eventually exhaust their nutrients, the phytoplankton die, sink and decompose. The decomposition process depletes surrounding waters of available oxygen, which marine animals need to survive. These oxygen-depleted waters are often called “dead zones,” since animals either die from lack of oxygen or leave the area to find more habitable waters.

Some algae produce their own toxins and blooms of these species are harmful to people. These harmful algal blooms, or HABs, can cause respiratory distress and illness in people and animals and can lead to shellfish closures. HABs cause an estimated $82 million in economic losses to the seafood, restaurant, and tourism industries each year.

In Florida Keys, you can report unusual events such as fish kills and phytoplankton blooms to the Marine Ecosystem Event Response Assessment, or MEERA.

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