What Is Plankton? Definition and Examples

What Is Plankton - Definition and Examples
Plankton consists of organisms that drift with tides and currents. Examples include fish fry, krill, jellyfish, and certain plants and algae.

Plankton is the collection of organisms that drift with tides and currents. Two important groups are phytoplankton (plant-like) and zooplankton (animal-life), but plankton include species from all the kingdoms of life, plus viruses. German biologist Victor Hensen coined the term plankton in 1887 by shortening the word halyplankton, which combines Greek words meaning “sea” and “to wander of drift”. Some plankton do propel themselves in water (or wind), but currents largely determine their position. Most plankton are microscopic and live in the ocean, but some organisms are large (such as jellyfish) and some live in freshwater or air.

  • Plankton are organisms that drift with water or wind currents.
  • Plankton is the plural term. A single organism is a plankter.
  • The study of plankton is planktology.
  • The two main types of plankton are phytoplankton (plant-like) and zooplankton (animal-like), but there are other categories and methods of classification.
  • Plankton are critical for the environment because they are key players in the carbon cycle, oxygen cycle, and nutrient cycling.
neuston, plankton, nekton, and benthos
The four categories of organisms are neuston, plankton, nekton, and benthos. (Zappys Technology Solutions, CC 2.0 Generic)

Plankton Definition and Examples

Plankton are a diverse group of organisms that are characterized by drifting in currents. In contrast, nekton organisms swim against current and control their position. Neuston organisms live at the interface between air and water and are not considered to be plankton, even though they may be subject to currents. Benthos organisms life on the ocean floor.

  • Neuston: Lives at the air-water interface. Examples include the Portuguese man o’ war, insects, and sea birds.
  • Plankton: Plankton live anywhere between the surface and the group. Examples include jellyfish, krill, fish eggs, salps, and the larval forms of crabs and octopuses.
  • Nekton: Nekton are free-swimming and powerful enough that they can escape currents. Examples include adult fish, squids, and whales.
  • Benthos: Benthos live on or within the sea floor or river bed. Examples include most plants, kelp, adult crustaceans, an adult echinoderms like starfish.

Types of Plankton

There are multiple ways of classifying plankton. The most common method is by trophic group (feeding strategy). Other methods distinguish species by life cycle, physical size, or by habitat.

Trophic Groups

  • Phytoplankton: Phytoplankton are autotropic (usually photosynthetic) organisms. Examples include algae, cyanobacteria, dinoflagellates, and diatoms.
  • Zooplankton: Zooplankton are small animals or protozoa. Examples include crustaceans, fish fry, eggs, and worms. They feed on each other or on phytoplankton.
  • Mycoplankton: These are fungi, which mainly feed on decaying matter.
  • Bacteriaplankton: These are bacteria and archea, which remineralize organic matter.
  • Virioplankton: These are viruses.
  • Mixoplankton: These are organisms that either acts as both producers and consumers or else switch between trophic groups.

Life Cycle

  • Holoplankton: These organisms spend their entire life cycle as plankton. The group include jellyfish, copepods, and most algae.
  • Meroplankton: These organisms are planktic for a portion of the life cycle. Examples include starfish, fish, and crustaceans.

Size Groups

  • Megaplankton: Megaplankton are greater than 20 cm in size. Jellyfish and salps are good examples.
  • Macroplankton: Macroplankton range between 2 and 20 cm in size. Examples include some tunicates and cephalopods.
  • Mesoplankton: These are barely visible to the naked eye, ranging between 0.2 and 20 millimeters.
  • Microplankton: This is the group of microscopic plankton, ranging between 20 and 200 micometers.
  • Nanoplankton: These tiny organisms are between 2 and 20 microns. It includes small diatoms and protists.
  • Picoplankton: This group is between 0.2 and 2 micros. It includes bacteria, some small eukaryotic protists, and certain golden algae.
  • Femtoplankton: These organisms are smaller than 0.2 microns. This group include virsues.

Habitat Groups

  • Marine plankton: Marine plankton inhabit oceans and the brackish waters of saltmarshes and estuaries. T
  • Freshwater plankton: These are drifting organisms in rivers, lakes, and ponds.
  • Aeroplankton: The wind carries aeroplankton. Examples include wind-borne seeds, pollen, spores, fungi, bacteria, and viruses.
  • Geoplankton: Geoplankton inhabit the tiny (often microscopic) reservoirs of moisture in terrestrial environments. Examples include tardigrades, rotifers, gastrotrichs, seed shrimp, and copepods. Most species go dormant when dry and become active when water becomes available again.

Plankton Importance

Plankton play a critical role in sustaining ecosystems and maintaining the planet’s health. They serve as the foundation of aquatic food webs, contribute significantly to global biogeochemical cycles, and support biodiversity.

  • Role in the food chain: Plankton, particularly phytoplankton, form the base of the marine and freshwater food chains. They are primary producers, converting sunlight into energy through photosynthesis and providing essential nutrients for various marine and freshwater species. Zooplankton consume phytoplankton and serve as a food source for larger organisms, such as fish, birds, and marine mammals. The abundance and distribution of plankton have a direct impact on the health and productivity of entire ecosystems.
  • Carbon cycle: Phytoplankton play a vital role in the global carbon cycle by sequestering carbon dioxide (CO2) from the atmosphere during photosynthesis. When plankton die, they sink to the ocean floor, where a portion of the carbon they contain becomes trapped in sediments, effectively removing it from the atmosphere. This process, called the biological pump, helps regulate atmospheric carbon dioxide levels and mitigate climate change.
  • Oxygen cycle: As photosynthetic organisms, phytoplankton produce oxygen (O2) as a byproduct of photosynthesis. This process maintains oxygen levels in both aquatic environments and the atmosphere. Phytoplankton produce approximately 50% of the Earth’s oxygen, making them essential contributors to the oxygen cycle and the planet’s overall atmospheric composition.
  • Nutrient Recycling: Plankton contribute significantly to nutrient cycling in aquatic ecosystems. As they die and decompose, plankton release essential nutrients, such as nitrogen, phosphorus, and iron, back into the water. This recycling process maintains the availability of these nutrients for other organisms and supports the overall productivity of the ecosystem. Some species of plankton, particularly cyanobacteria, fix atmospheric nitrogen, converting it into a form that can be used by other living organisms.


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