Plankton vs. Krill: How Are They Different?

Written by Kyle Glatz
Published: October 21, 2022
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Plankton are incredibly diverse and important beings even though they are some of the smallest ones on earth. They are found in our water and air, and they greatly contribute to the food chain. However, there is a fair amount of confusion about what are plankton and the individual creatures that fall under that umbrella term. That’s why we’re going to spend some time looking at plankton vs. krill.

We’ll show you where krill fits into the discussion about plankton, including how they are alike and what makes them different. By the time we have finished, you’ll know how to tell these two beings apart.

Comparing Plankton vs. Krill

PlanktonKrill
SizeWeight: Less than an ounce
Length: Most often less than 1 inch, but they can grow several feet
Weight: Less than an ounce
Length: Most measure between 0.4 and 0.8 inches, but some measure up to 2.4 inches
Phylogenetic Family– Include 20,000 species in 8 taxonomic groups– Families Euphausiidae and Bentheuphausiidae
– 11 different genera and dozens of species
– Considered a type of zooplankton, especially in their larval form
Diet– Phytoplankton rely on photosynthesis and also absorb valuable nutrients from their environment
– Zooplankton consume phytoplankton, bacteria, and algae
– Eat algae, phytoplankton, zooplankton, copepods, and fish larvae
Locomotion– None
– Float with the current
Propel themselves with a swimming motion
Predators– Whales, zooplankton, salmon, crustaceans, coral, sharks, and many other creatures in the oceansWhales, various seabirds, seals, and squid
– Considered one of the most significant creatures in the ocean food chain

The 5 Key Differences Between Plankton and Krill

Animals that glow – krill

Krill are small shrimp-like creatures which can reach around 2.5 inches long

©RLS Photo/Shutterstock.com

The most significant differences between plankton and krill can be found in their size and phylogenetic families. All krill are plankton, but not all plankton are considered krill. Krill are small, shrimp-like creatures that come from two phylogenetic families, Euphausiidae and Bentheuphausiidae. Meanwhile, over 20,000 species from eight taxonomic groups exist in the world, representing far more families and genera than krill.

However, krill are larger than many types of plankton. The average krill measures between 0.4 and 0.8 inches, but some of the largest measure 2.4 inches long or more. Many types of plankton weigh less than an ounce and grow less than an inch in length.

Jellyfish are gelatinous zooplankton that drift in the ocean with limited locomotion and can reach several feet long. Thus, while some sorts of plankton are larger than krill, a vast number of them are smaller.

Plankton vs. Krill: Phylogenetic Family

Generally speaking, plankton comprises small organisms that cannot propel themselves against a current. That can apply to creatures at a short period of time in their lifecycle, like fish eggs or krill larvae, or it can apply to creatures throughout the course of their lifecycle.

In fact, over 20,000 species across eight taxonomic groups can be considered plankton. Plankton are incredibly diverse. Krill are less diverse. Only two families and 11 different genera of creatures are considered krill. Specifically, krill come from the Euphausiidae and Bentheuphausiidae families, but they are considered plankton in their larval forms.

Plankton vs. Krill: Size

Several types of plankton are larger than krill, but most of them are smaller. The average krill measures between 0.4 and 0.8 inches in length. Although some of them can grow over two inches long, it’s not their average size. For the most part, they weigh less than an ounce.

Most types of plankton weigh less than an ounce. Some of them can weigh far more than that, like jellyfish. Also, while many sorts of plankton measure less than one inch long, some of them can grow several feet long! So, it’s fair to say that you can find plankton longer than krill, but most krill are still larger than the average plankter.

Plankton vs. Krill: Diet

Juvenile krill are a form of zooplankton, and they feed on algae, phytoplankton, other zooplankton, fish larvae, and other foods. Meanwhile, plankton has a more diverse diet. Phytoplankton, small plants, use photosynthesis to produce energy. They can also absorb some nutrients from their environment.

Some zooplankton have similar diets to krill, and they also consume bacteria, algae, and more. All in all, krill have a similar diet to other zooplankton since they are very similar creatures.  

Plankton vs. Krill: Locomotion

What Do Sea Monkeys Eat - Collection of Brine Shrimp

Most plankton are tiny little organisms. They are so small they are incapable of propelling against water currents.

©iStock.com/antpkr

One of the defining features of plankton is that it cannot propel itself against a current. However, that is not the case with adult krill, and that is why they’re sometimes considered micro-nektonic creatures rather than plankton.

Adult krill can use their swimmerets to propel themselves to a degree. Still, they are only capable of propelling themselves against a weak current. However, even when massive groups of them form, they are still subject to powerful ocean currents.

Plankton vs. Krill: Predators

Plankton and krill are both important members of the food chain. Phytoplankton are eaten by zooplankton, like krill, and those zooplankton grow to become a major source of food for larger creatures, like fish.

Also, some filter-feeding animals, like baleen whales, consume vast amounts of zooplankton, especially krill, to sustain themselves. Krill are considered some of the most significant creatures in the oceanic food chain, sustaining small and large creatures alike.

They are commonly eaten by whales, seals, squid, seabirds, and more. The vast majority of krill are consumed by whales and penguins.

All told, plankton and krill have similar features. That’s mostly because krill have many plankton-like qualities. Although krill have some similarities to plankton, they also consume plankton. Major differences are found in their size, locomotion, and phylogenetic families, and those are the simplest ways to tell one from another.

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The photo featured at the top of this post is © Apple Pho/Shutterstock.com


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About the Author

Kyle Glatz is a writer at A-Z-Animals where his primary focus is on geography and mammals. Kyle has been writing for researching and writing about animals and numerous other topics for 10 years, and he holds a Bachelor's Degree in English and Education from Rowan University. A resident of New Jersey, Kyle enjoys reading, writing, and playing video games.

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Sources
  1. Nature, Available here: https://www.nature.com/articles/s41467-019-12668-7
  2. NOAA Fisheries, Available here: https://oceanservice.noaa.gov/facts/plankton.html#:~:text=Plankton%20are%20usually%20microscopic%2C%20often,like%20some%20crustaceans%20and%20jellyfish.
  3. Commission for the Conservation of Antarctic Marine Living Resources, Available here: https://www.ccamlr.org/en/fisheries/krill-%E2%80%93-biology-ecology-and-fishing#:~:text=Why%20are%20krill%20so%20important,primary%20production%20within%20their%20range.
  4. Harvard, Available here: https://ui.adsabs.harvard.edu/abs/2019APS..DFDC27003C/abstract