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What Are Plankton?

Humpbacks are one of the many whale species that feed on plankton.
Jellyfish are zooplankton.
Water fleas (Cladocera) are an order of microscopic crustaceans.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 03 October 2014
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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.

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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.

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Discuss this Article

anon265201
Post 13

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

anon130359
Post 11

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

anon125208
Post 10

nice. helped with my homework.

anon113795
Post 8

what is the function of plankton?

anon80230
Post 7

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!

anon44321
Post 6

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

anon43621
Post 4

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

anon42971
Post 3

what are the characteristics of plankton?

anon42960
Post 2

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

anon17776
Post 1

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

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