Small but mighty – plankton help keep the blue heart of the planet running

Plankton
Plankton

Planktons is tiny plants and animals are some of the most important organisms in the sea. Plankton is a group of marine and freshwater organisms that drift along ocean currents because they are too small or weak to swim against them. Their name comes from the Greek word plankton which means “wandering.” The range in size is from 2 micrometres (that’s smaller than a human red blood cell!) to more than 20 centimetres. There are two types of plankton: phytoplankton, which is tiny plants, and zooplankton, which are tiny animals.

Plankton: Small Organisms with a Big Role in the Ocean

Phytoplankton is so small that you need a microscope to see them. Types of phytoplankton include dinoflagellates, diatoms, cyanobacteria and green algae. Just like land plants, they contain chlorophyll and need sunlight and nutrients to grow. However, too much of a good thing (like excess nutrients, including those from human-driven nutrient pollution) can contribute to algae blooms, where colonies of phytoplankton grow in large quantities.

Plankton
Plankton

Planktons, although not all algal blooms are harmful, some contain toxins that can cause serious problems for the ecosystem and the communities that rely on them. Harmful algal blooms (or HABs) produce toxins that can kill fish, shellfish, birds and more, and can make humans very, very sick if ingested. (Read more about the devastating HAB in Florida in 2018).

Zooplankton, on the other hand, is small animals. Some are small enough that you need a microscope to observe them, but others you can see with the naked eye. There are two categories of zooplankton: holoplankton, or animals that spend their entire lives as plankton like copepods and rotifers, and meroplankton, or animals that are only planktonic for a short time like larval fish and crustaceans.

Plankton Small Organism
Plankton Small Organism

Image Source: Wikimedia

What is plankton’s role in the ecosystem?

Plankton is at the base of the food chain, meaning they are critical in supporting marine and freshwater food webs. Phytoplankton is also primary produces, meaning they use photosynthesis to convert carbon dioxide to oxygen, and are responsible for up to half of the oxygen we breathe. Phytoplankton is eaten by small zooplankton, which is in turn eaten by other zooplankton. That plankton is eaten by small fish and crustaceans, which in turn are eaten by larger predators, and so on. Large animals can eat plankton directly, too—blue whales can eat up to 4.5 tons of krill, large zooplankton, every day. Without plankton, entire food webs around the world would likely collapse.

Plankton are a group of marine and freshwater organisms
Plankton are a group of marine and freshwater organisms

Image Source: © MATT WILSON/JAY CLARK, NOAA NMFS AFSC

Unfortunately, planktons abundance has been decreasing. Scientists believe phytoplankton numbers have decreased about 40% since 1950. Changes in ocean temperature and ocean acidification threaten plankton health, which in turn has major implications for marine food webs and oxygen production.

Source: Ocean Conservancy

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