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What Are Phytoplankton?

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Microscopic Phytoplankton

What Are Phytoplankton?

Phytoplankton, also known as microalgae, are microscopic biotic organisms that inhabit most bodies of water, including the oceans, lakes, rivers and ponds. They are most commonly found floating on the surface of water, as these organisms need sunlight in order to produce nutrients. These organisms convert carbon dioxide into chemical energy through photosynthesis.

These organisms, in the same way that plants do, obtain their energy from the sun through the process of photosynthesis; for these process to occur, they must live close to the surface of a body of water or the euphotic zone, where they will use sunlight and inorganic nutrients to produce proteins, fats and carbohydrates.

Primary Producers in the Aquatic Web System

Phytoplankton are too small and can only be observed with a microscope but they can also be observed when they grow in huge quantities in a process known as bloom. When they do, satellite photos show them as patches of bluish or green colors in the oceans, lakes or rivers; even in ponds.

These microorganisms are the primary source of food in the aquatic food web. Every other organism, microscopic, such as zooplankton or big, including fish and whales, feed on phytoplankton. Not all phytoplankton is safe for feeding, as some can produce toxins and kill marine life, that is the case of red tides; the name with which harmful algae blooms are known.

The Flora of the Water World

Phytoplankton or microalgae are tiny organisms that drift with water currents. Like continental vegetation, phytoplankton utilizes CO2 and nutrients to a form that other animal species can use; in the process, oxygen is released. These microscopic flora-green algae-often can be seen in rivers, lakes and ponds. Cyanobacteria-blue-green algae may change the taste of water.


It's believed that phytoplankton may contribute to an estimate of 50-80% of the oxygen in the earth's atmosphere. Among the most common types of cyanobacteria are green algae, silica encased diatoms, dinoflagellates and coccolithophores. Population in the ocean have rising and falling based on cycles lasting anywhere from years to decades. Rising sea surface temperatures are the main cause of this; Phytoplankton population is known to increase in Spring and fall due to an increase in light, temperature and water minerals.

Phytoplankton are a more diverse group than terrestrial vegetation where most autotrophs are plants. Phytoplankton comprises protistan eukaryotes, eubacteria and archaebacteria prokaryotes. It's been estimated that there are approximately 5,000 species of aquatic phytoplankton in the world.

Algal Bloom

Importance of Phytoplankton

Microalgae are at the base of the aquatic food system. Every creature in the water system feeds on them; from microscopic zooplankton to small fish and whales. They are capable of converting the sun's energy into chemical energy that is stored as sugars. These chemical energy is then consumed by heterotrophs-those that are not able to produce their own food, such as zooplankton and most marine animals.

They produce almost half of the photosynthetic energy-that is to say they convert half of the carbon dioxide present in the atmosphere into chemical energy. They help keep carbon dioxide levels in the atmosphere and thus reduce the greenhouse effect. It´s believed that the oceans absorbe anywhere between 30-50% of the CO2 produced by the consumption of fossil fuel.

Climate and the Carbon Cycle

Climate change is caused by the emission of CO2 and other greenhouse gases into the atmosphere by industry. The rate at which CO2 is absorved into the atmosphere depends on how much is emitted and the quantity that is absorved by plants and soil or is transported to the ocean by phytoplankton and sea animals. Phytoplankton uses CO2 through photosynthesis. CO2 is transported to varied layers of the ocean by other sea animals that consume phytoplanton.

Phytoplankton dynamics occurs within the first 50 meters of the ocean´s surface and varies based on the season and geographical location; this is determined by the amount of sunlight that is received and the oceean´s temperature. The lack of nutrients and minerals also determines the growth of phytoplankton. Zooplankton-the microscopic organisms that feed on phytoplankton also determine the rate of growth of phytoplankton.

Check Your Knowledge of Phytoplankton

For each question, choose the best answer. The answer key is below.

  1. They are the primary producers in the Aquatic Food Web
    • Krill
    • Shrimp
    • Phytoplankton
  2. This is another name for phytoplankton
    • Microalgae
    • Cyanobacteria
    • Green algae
  3. This refers to explosive growth of phytoplankton
    • Algal explosion
    • Red tide
    • Aquatic growth
  4. Phytoplankton can be noticed from satellites when they...
    • Bloom
    • Explode
    • Float
  5. Phytoplankton contributes to the oxygen on earth´s atmosphere with...
    • 40-70%
    • 50-80%
    • 30-50%

Answer Key

  1. Phytoplankton
  2. Microalgae
  3. Red tide
  4. Bloom
  5. 50-80%

Carbon Cycle

Chorophil Concentrations in Phytoplankton

Satellites play an important role at monitoring phytoplankton concentrations. Microscopic phytoplankton are microscopic organisms and can not be seen without the aid of a microscope but when they bloom, they grow by the billions and due that they contain chorophyll and other pigments, they may reflect light in various eye catching colors; bluish, reddish and greenish.

All of these colors are used by scientists to calculate chlorophyl concentration and biomass of phytoplankton present at that spot in the ocean.

The Potential of Phytoplankton

© 2018 Jose Juan Gutierrez

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