Plankton

Plankton are tiny living things that float in water or air. They cannot move against strong currents or winds. You can find them in oceans, lakes, rivers, and even in the air we breathe. The word "plankton" comes from a Greek word meaning "drifter" or "wanderer." This name fits because these organisms move with the flow.

Plankton include many different kinds of life. Some are very small, like bacteria and algae. Others are bigger, like jellyfish. Scientists group plankton by how they live and move, not by what they are. Some plankton make their own food, like plants. Others eat other organisms. Recently, scientists discovered that some plankton can do both, making them a special group.

Even though they are tiny, plankton are very important for life on Earth. The smallest plankton help make much of the world’s oxygen and take in carbon dioxide. This helps keep our planet healthy. Plankton are the base of the food chain, supporting fish, whales, and many other animals. In the air, tiny particles like pollen and seeds drift along and play a part in nature’s cycle.

Overview

Plankton are tiny living things that float in water, like in oceans, seas, rivers, and lakes. They can't swim against the current, so they move with the water.

Most plankton are so small you can only see them with a microscope. They are very important for the ocean. They help keep the water balanced and make a lot of the world's oxygen. Some plankton live their whole lives floating, while others float only for part of their lives before settling on the ocean floor or swimming away.

By habitat

Aeroplankton

Main article: Aeroplankton

Aeroplankton are tiny living things that float in the air, carried by the current of the wind. They are like the atmospheric analogue to oceanic plankton. Most are very small, even microscopic, so they are hard to see. Scientists collect them using traps and nets from aircraft, kites, or balloons. Aeroplankton includes many microbes, such as viruses, many types of bacteria, kinds of fungi, and species of protists, algae, mosses, and liverworts. These can be spores, pollen, or wind-scattered seeds.

Freshwater plankton

Freshwater plankton are similar to marine plankton but live in lakes and rivers instead of oceans.

Geoplankton

See also: Geoplankton

Many small animals live on land by thriving in tiny pockets of water. These include rotifers and gastrotrichs, which can survive dry periods by laying tough eggs. Some can even stop growing and survive for years. Water bears can also stop growing during dry times and live for decades. Many tiny crustaceans, like copepods and amphipods, and seed shrimp, can survive dry times by going dormant and living in small water pockets.

Marine plankton

Marine plankton includes marine protists (algae and protozoa), small drifting animals, marine prokaryotes (bacteria and archaea), and marine viruses that live in the salty waters of oceans and estuaries.

At the ocean surface

Further information: Neuston

Plankton can also be found at the ocean surface. Organisms that live at or just below the surface are called neuston. They float on top of the water (epineuston) or swim in the top few centimeters (hyponeuston). Many neuston drift with currents or wind because they cannot swim strongly against them.

Neustonic animals often float upside down on the ocean surface and are an important part of the zooplankton community. They help move energy between the surface and deeper layers of the ocean and serve as food for fish and seabirds.

In deep ocean

In 2025, researchers found tiny living communities in the deep ocean, even at great depths. Ocean currents move water and tiny creatures around the world. Water samples taken from deep in the South Pacific Ocean showed more types of tiny creatures about 300 meters deep. These microbes have special traits to live in cold, high-pressure water or in areas with very little oxygen.

By taxon

Plankton are tiny living things that float in water or air. They are not a special group of animals or plants, but they can be sorted into different types.

Some plankton are tiny animals, like arrow worms and water fleas. Others are single-celled creatures called protists, such as diatoms and algae. There are also planktonic fungi and tiny bacteria, which help recycle nutrients in the water. Even tiny viruses that infect other tiny creatures are part of plankton. Each type of plankton plays an important role in the water's ecosystem.

By size

Plankton can be grouped by their size. Some very small plankton, called microplankton, need a microscope to see them. These tiny creatures help form the base of the ocean's food chain. Even smaller plankton, called nanoplancton, were discovered in the 1980s and are very numerous.

Microplankton include some types of diatoms, which are a key part of phytoplankton. There is also a special bacteria called Pelagibacter ubique that is very common in the ocean and helps with the Earth's carbon cycles. Some tiny creatures like the sea sparkle dinoflagellate can glow at night, creating a beautiful milky seas effect.

Larger plankton are called macroplankton. These include animals like the amphipod Hyperia macrocephala, the sea walnut ctenophore, and seaweed like Sargassum that floats using air bladders.

By trophic mode

Trophic mode shows how plankton get energy and nutrients. Plankton are divided into four groups: phytoplankton, zooplankton, mixoplankton, and decomposers.

Phytoplankton

Phytoplankton are tiny plants or algae that float near the water's surface. They need sunlight to make their own food through photosynthesis. Important types include diatoms, cyanobacteria, dinoflagellates, and coccolithophores. Phytoplankton are the base of the marine food web, feeding many other sea creatures.

Zooplankton

Zooplankton are small animals or animal-like organisms that eat other plankton. They include tiny creatures like protozoans, crustaceans, and the eggs and larvae of larger animals such as fish. Zooplankton are important because they eat phytoplankton and are eaten by larger animals.

Mixoplankton

Mixoplankton can act like both phytoplankton and zooplankton. They make their own food like phytoplankton when conditions are good, but they can also eat other plankton when times are hard. This helps them survive in changing environments.

Decomposers

Decomposers break down dead organisms and recycle nutrients back into the water. This includes tiny fungi and bacteria that help keep the water clean and support plant growth.

Gelatinous zooplankton

Gelatinous zooplankton are delicate, often transparent animals without hard bodies. They include jellyfish, ctenophores, salps, and Chaetognatha. These creatures drift in the ocean and are easily damaged.

Ichthyoplankton

Ichthyoplankton are the eggs and larvae of fish. They float in the upper layers of the water because they cannot swim well on their own. Fish eggs carry their own food supply, while larvae eat smaller plankton until they grow big enough to swim away.

Pseudoplankton

Pseudoplankton are organisms that attach to floating objects or other plankton. They cannot float on their own, unlike true plankton. Examples include goose barnacles and certain bryozoans.

Tychoplankton

Tychoplankton are organisms that are normally attached to the bottom or live freely but get swept into the water by currents or disturbances. They are not true plankton but can be found floating temporarily.

Mineralized plankton

Some plankton have hard shells made of minerals. Diatoms have glass shells, coccolithophores have chalk plates, and foraminiferans have calcium carbonate shells. These shells can become important parts of rocks and landscapes.

By life cycle

Holoplankton

Holoplankton spend their whole lives drifting as plankton. Examples include some diatoms, dinoflagellates, copepods, and salps. They live in the open water and can be plant-like or animal-like.

Meroplankton

Meroplankton spend only part of their lives as plankton. They start as plankton but later grow into larger animals that live on the seafloor or swim actively. Many sea creatures, like insects and shellfish, begin life as meroplankton before settling down or swimming away.

Ecology

Plankton are important parts of the food chain in the water. They are at the bottom of the chain and help feed many bigger animals, like fish. Plankton also help control important gases in the air and water, like carbon dioxide and oxygen.

Plankton help move nutrients and energy through the water. Tiny plants called phytoplankton make their own food using sunlight. Tiny animals called zooplankton eat these plants, and then bigger animals eat the zooplankton. There are also tiny organisms like bacteria and viruses that help move nutrients around in their own ways.

Phytoplankton are very important because they make a lot of the oxygen we breathe. They use sunlight to turn carbon dioxide into oxygen, which they release into the water and air. This process has helped keep the air full of oxygen for a very long time.

Biomass variability

Phytoplankton are tiny plants that float in the water. They grow when they have enough light and nutrients. In warm tropical areas of the ocean, they need more nutrients to grow well. In colder areas, they need more light.

Changes in the environment, like during El Niño events, can cause phytoplankton numbers to drop. This can affect animals that eat them, such as zooplankton, fish, seabirds, and marine mammals.

Scientists are studying how warming oceans may change phytoplankton populations. They look at how changes in water layers, temperature, and nutrient supply might impact these tiny plants. They also study how animals that eat phytoplankton might change their eating habits.

Planktonic relationships

Fish and plankton

Zooplankton are the first food for baby fish when they start eating. Fish need zooplankton to be available so they don’t go hungry. Things like ocean currents, temperature changes, river dams, ocean acidification, and rising temperatures can change zooplankton numbers. This affects baby fish survival and how well fish can have babies.

Plankton can be found in patches in the ocean where there aren’t many fish. Where there are lots of fish, how much the fish eat zooplankton affects how the zooplankton act. Depending on how much fish are eating, zooplankton might act in regular ways or in more unpredictable ways.

Baby fish can also affect plankton blooms by eating fewer zooplankton. This lets tiny plants in the water, called phytoplankton, grow more. This helps the bloom last longer.

In fish farms, plankton are very important. Farmers have used plankton to help raise fish for many years. This shows how useful plankton are even in places where humans control the environment.

Whales and plankton

Whale poop helps provide nutrients for tiny plants in the ocean called phytoplankton. Phytoplankton are at the start of the ocean food chain. They are eaten by zooplankton and krill, which are then eaten by bigger animals, including whales. So, whale poop helps feed the whole ocean food web.

Humans and plankton

Plankton have big effects on people. About 70% of the oxygen we breathe comes from phytoplankton in the oceans. Plankton are the base of the ocean food web, feeding all the animals above them.

Sometimes, plankton can carry harmful germs that make people sick.

Plankton Manifesto

In 2024, experts made a plan called the Plankton Manifesto. This plan has ideas to help protect plankton and use them to solve big problems like climate change, pollution, and biodiversity loss.

The Manifesto says plankton are very important because they are the base of marine ecosystems. They help make about half of the oxygen we breathe.

Some main ideas in the Manifesto are:

• Using new tools like DNA sequencing, bioinformatics, satellite monitoring, and AI image analysis to learn more about plankton.
• Finding new ways to use plankton, like cleaning water, making bioplastics, creating fertilizers, and feeding animals.
• Asking leaders and groups to include plankton in plans to fight climate change and protect nature, especially at big meetings like COP29, COP16, and the 2025 United Nations Ocean Conference.
• Teaching people more about plankton through schools and projects to show how they help with food security and ecosystem health.
• Working together between different groups like scientists, companies, and governments to study plankton and keep them safe from problems like nutrient pollution and ocean warming.