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What are Plankton?

Mary McMahon
By
Updated May 17, 2024
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The word “plankton” is an umbrella term for organisms that live their lives adrift in the water and are unable to move independently. The term comes from an Ancient Greek word which means “floating,” and these organisms do indeed float through bodies of water both fresh and salty around the world. Primarily, plankton live in the sunlit zone of the ocean, although some species are found in much deeper water. They are very important to life on Earth, as they serve as the bottom of the food chain. They nourish larger animals, which are in turn eaten by even bigger animals, and so on up to organisms like humans at the top of the food chain. Plankton are also responsible for the Earth's atmosphere, thanks to the efforts of billions of photosynthesizing phytoplankton.

There are three loose categories of plankton, although the nebulous identities of some species make them difficult to categorize. Phytoplankton are those with plant-like characteristics, such as diatoms. They photosynthesize for energy, and are sometimes found in large groups termed blooms. Many are unicellular, and are very simple animals.

Zooplankton possess animal-like characteristics, and can sometimes get very large. Jellyfish, for example, are zooplankton because, while they are larger than many other plankton, they too are at the mercy of the ocean's currents. Most eat phytoplankton for energy, and in turn serve as an energy source for larger animals in the ocean, such as whales. As organisms like the dinoflagellates demonstrate, some zooplankton are capable of limited motion, but they are still unable to resist currents of water.

Bacterioplankton are the third group. Like their counterparts on land, they consume waste products from other organisms. They can also photosynthesize for energy, and some species, such as those found by hydrothermal vents, are capable of chemosynthesis. They are also eaten by zooplankton.

Once categorized, there are two more divisions of these organisms. The first is the group of holoplankton, organisms that remain plankton for their entire lives. The second is meroplankton, larval forms of sea creatures like shellfish, fish, crustaceans, and many others. In their early stages, these larvae drift through the water, usually powerless to move, until they develop into older animals.

Although small, plankton play an important role in the health of the planet. Just like other organisms, they require nutrients and a balanced environment to live in. Their absence in a body of water indicates an environmental imbalance, as does a disproportionate number of unusual plankton. For this reason, some scientists spend a lifetime researching them, and new species are constantly being discovered and studied.

Frequently Asked Questions

What exactly are plankton?

Plankton are a diverse group of microscopic organisms that drift or float in the water column of oceans, seas, and bodies of fresh water. They are the foundation of the aquatic food web, providing an essential source of food to many larger species, including fish, whales, and seabirds. Plankton can be categorized into phytoplankton (plant-like organisms that photosynthesize) and zooplankton (animal-like organisms that feed on other plankton).

How important are plankton to the ocean's ecosystems?

Plankton are critically important to marine ecosystems. Phytoplankton produce an estimated 50% of the world's oxygen through photosynthesis, according to the National Oceanic and Atmospheric Administration (NOAA). They also absorb carbon dioxide, helping to regulate the Earth's climate. Zooplankton, as primary consumers, transfer energy from phytoplankton to higher trophic levels, sustaining the diets of many marine animals.

Can plankton be seen with the naked eye?

While most plankton are microscopic and cannot be seen with the naked eye, there are exceptions. Some plankton, like certain types of jellyfish and the larvae of larger animals, can grow to be several inches in size and are visible to the unaided eye. However, to observe the vast majority of plankton species, a microscope is necessary.

Do plankton live everywhere in the ocean?

Plankton are found throughout the world's oceans, from the surface to the deep sea, although their density and diversity can vary greatly. Phytoplankton are most abundant in the sunlit upper layers of the ocean where sunlight can penetrate for photosynthesis. Zooplankton distribution can be influenced by factors such as water temperature, salinity, and the presence of predators or prey.

How do plankton affect the carbon cycle?

Plankton play a significant role in the carbon cycle. Phytoplankton absorb carbon dioxide from the atmosphere during photosynthesis, converting it into organic carbon. When plankton die or are consumed, this carbon can sink to the ocean floor as part of marine snow, effectively sequestering it and reducing atmospheric CO2 levels. This process is a key component of the biological carbon pump.

Are plankton populations stable or are they affected by environmental changes?

Plankton populations are sensitive to environmental changes such as ocean acidification, warming waters, and pollution. Studies have shown that climate change is impacting plankton communities, with shifts in distribution and seasonal abundance patterns. These changes can have cascading effects on marine ecosystems, as plankton are integral to food webs and global biogeochemical cycles.

WiseGEEK is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon265201 — On May 01, 2012

I'm after the characteristics as well for a scientific report! Very hard to find.

By anon130359 — On Nov 28, 2010

What are some ways in which plankton adapt to reduce their sinking rates?

By anon125208 — On Nov 08, 2010

nice. helped with my homework.

By anon113795 — On Sep 26, 2010

what is the function of plankton?

By anon80230 — On Apr 26, 2010

This is very useful and i understand it and all, but what i want to know is what the characteristics are and why they are soo important. this is a cool website!

By anon44321 — On Sep 07, 2009

what are the characteristics of plankton and what are their importance to the coastal zone ecology?

By anon43621 — On Aug 31, 2009

what are the characteristics of plankton and what is their importance to the zone ecology?

By anon42971 — On Aug 25, 2009

what are the characteristics of plankton?

By anon42960 — On Aug 24, 2009

what are the characteristics of plankton and what is their importance to the coastal zone ecology?

By anon17776 — On Sep 07, 2008

what are the characteristics of plankton and what is their importance to the coastal zone ecology?

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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