Krill vs. Plankton

What's the Difference?

Krill and plankton are both small organisms that play a crucial role in marine ecosystems. However, there are some key differences between them. Krill are small, shrimp-like crustaceans that belong to the order Euphausiacea, while plankton refers to a diverse group of microscopic organisms that drift in the water column. Krill are larger in size compared to most plankton, with an average length of a few centimeters. They are also more active swimmers and have a more complex anatomy. Plankton, on the other hand, encompass a wide range of organisms, including bacteria, algae, and small animals. They are typically passively carried by ocean currents. Despite these differences, both krill and plankton serve as a vital food source for many marine animals, forming the base of the ocean food chain.


ClassificationEuphausiaceaVarious groups (e.g., diatoms, dinoflagellates)
SizeApproximately 1-6 cmMicroscopic to macroscopic
Feeding BehaviorFilter feedersVaries depending on type (e.g., autotrophs, heterotrophs)
HabitatMarine environments, primarily in cold watersFound in various aquatic habitats (e.g., freshwater, marine)
Role in Food ChainPrimary consumers, important prey for many marine animalsPrimary producers (e.g., photosynthetic plankton) or consumers (e.g., zooplankton)
ReproductionSexual reproduction, external fertilizationVaries depending on type (e.g., asexual reproduction, sexual reproduction)
MobilitySwimming, often in large groupsVaries depending on type (e.g., some are motile, while others are non-motile)

Further Detail


When it comes to marine ecosystems, two important organisms that play a crucial role are krill and plankton. Both krill and plankton are tiny organisms that form the base of the food chain in the ocean. While they may seem similar at first glance, there are several key differences between these two organisms. In this article, we will explore the attributes of krill and plankton, highlighting their unique characteristics and contributions to the marine ecosystem.

Physical Characteristics

Krill are small, shrimp-like crustaceans that belong to the order Euphausiacea. They typically measure around 1-6 centimeters in length and have a translucent body. Krill possess a hard exoskeleton, segmented bodies, and multiple pairs of legs. They also have large compound eyes and two pairs of antennae that help them navigate their surroundings. On the other hand, plankton refers to a diverse group of organisms that are mostly microscopic in size. They can be classified into two main categories: phytoplankton, which are photosynthetic, and zooplankton, which are heterotrophic. Phytoplankton are single-celled algae, while zooplankton can include various organisms such as tiny crustaceans, larval fish, and jellyfish.

Habitat and Distribution

Krill are found in all the world's oceans, but they are most abundant in cold, nutrient-rich waters such as the Southern Ocean surrounding Antarctica. They form massive swarms that can contain millions of individuals. Krill are known for their vertical migration, where they move up to the surface at night to feed on phytoplankton and then descend to deeper waters during the day to avoid predators. Plankton, on the other hand, are found throughout the ocean, from the surface waters to the deep sea. They are highly abundant in areas with high nutrient concentrations, such as upwelling zones and coastal areas. Planktonic organisms are carried by ocean currents, allowing them to disperse widely across the globe.

Feeding Behavior

Krill are omnivorous organisms that primarily feed on phytoplankton, but they also consume zooplankton, small fish, and even other krill. They use their specialized appendages to filter tiny particles from the water, a feeding behavior known as filter-feeding. Krill play a vital role in transferring energy from primary producers, such as phytoplankton, to higher trophic levels in the food chain. Plankton, on the other hand, exhibit a wide range of feeding strategies depending on their type. Phytoplankton obtain energy through photosynthesis, using sunlight and nutrients to produce organic matter. Zooplankton, on the other hand, are heterotrophic and feed on other planktonic organisms, detritus, or even larger prey. Some zooplankton are filter-feeders like krill, while others are predators or scavengers.

Ecological Importance

Krill are considered a keystone species in the marine ecosystem. They serve as a vital food source for a wide range of marine organisms, including whales, seals, penguins, and fish. Their abundance and distribution have a significant impact on the entire food web, and any changes in krill populations can have cascading effects on higher trophic levels. Additionally, krill play a crucial role in the carbon cycle by sequestering carbon dioxide through their feeding and excretion processes. Plankton, too, are essential for the functioning of marine ecosystems. Phytoplankton are responsible for approximately half of the global primary production, producing oxygen and serving as the base of the marine food chain. Zooplankton, in turn, transfer energy from phytoplankton to higher trophic levels, contributing to the overall biodiversity and productivity of the oceans.

Commercial and Research Importance

Krill have gained significant commercial importance in recent years. They are harvested for various purposes, including human consumption, aquaculture feed, and as a source of omega-3 fatty acids. The oil extracted from krill is rich in omega-3s and is used in dietary supplements. However, the increasing demand for krill products has raised concerns about the sustainability of krill fisheries and their potential impact on marine ecosystems. Plankton, although not directly targeted for commercial purposes, are of immense research importance. Scientists study plankton to understand oceanic processes, monitor environmental changes, and assess the health of marine ecosystems. Planktonic organisms are also used as indicators of water quality and can provide valuable insights into the impacts of climate change on the oceans.


In conclusion, while krill and plankton are both vital components of marine ecosystems, they differ in several aspects. Krill are larger, shrimp-like crustaceans that filter-feed on phytoplankton and play a keystone role in the food web. Plankton, on the other hand, encompass a diverse group of organisms, including microscopic algae and small animals, which contribute to primary production and energy transfer in the oceans. Understanding the attributes and ecological importance of both krill and plankton is crucial for the conservation and sustainable management of marine resources.

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