What is the Difference Between Krill and Plankton

The main difference between krill and plankton is that krill are small crustaceans that consume both zooplankton and phytoplankton, whereas plankton is the diverse collection of organisms that serve as a crucial source of food at the bottom line of food chains. Furthermore, krill are the dominant planktonic food source of marine mammals.  

Krill and plankton are two small creatures that live in large water bodies. Generally, both of them represent the bottom line of marine food chains. 

Key Areas Covered 

1. Krill
     – Taxonomy, Characteristics, Importance
2. Plankton
     – Taxonomy, Characteristics, Importance
3. What are the Similarities Between Krill and Plankton
     – Outline of Common Features
4. What is the Difference Between Krill and Plankton
     – Comparison of Key Differences

Key Terms 

Food Chains, Krill, Phytoplankton, Plankton, Zooplankton

Krill – Taxonomy, Characteristics, Importance 

Krill are small, free-swimming, open-ocean crustaceans that belong to the order Euphausiacea under the phylum Arthropoda. Also, there are around 85 species of krill have been identified worldwide. Anatomically, krill have a body with three tagmata; cephalon, pereion, and pleon. They also have a chitinous exoskeleton, which is transparent in many species. Also, they have intricate compound eyes, two antennae, and several pairs of thoracic legs, including feeding legs and grooming legs. Besides, all species have five pairs of swimming legs similar to those in lobster or crayfish. However, the main distinguishing feature of krill and a true shrimp is the presence of externally-visible gills in the krill. In addition to these, the size of a krill can be 1-2 cm. 

Figure 1: Krill – Anatomy

Furthermore, krill serve as an important tropic level near the bottom of the aquatic food chains. Mainly, they feed on phytoplankton and to a lesser extent on zooplankton. Hence, krill convert plankton into a form of food source suitable for many large animals, making up the largest part of their diet. Significantly, Antarctic krill makes the largest total biomass of a single species on the planet. Although half of the biomass is eaten by whales, seals, penguins, squid, and fish each year, it is replaced through growth and reproduction. Specifically, Krill is the main prey of baleen whales such as the blue whale. 

Besides, krill form huge aggregates of adults called swarms, which stretch for kilometres in every direction, with many thousands of krill packed into each cubic meter of water, turning the water red or orange.  

Plankton – Taxonomy, Characteristics, Importance 

Plankton is a diverse collection of small organisms that live in large water bodies. However, they do not actively swim against a current but, freely float along with it. Besides, individual organisms in plankton are known as plankters. Generally, plankton includes drifting or floating animals, protozoans, algae, archaea, and bacteria. Therefore, plankton is not a taxonomic group but an ecological niche. On that account, plankton serves as a crucial food source to many small to large animals that live in water, including bivalves, fish, and whales. 

Figure 2: Tomopteris – A Genus of Marine Planktonic Polychaete

Moreover, there are two types of plankton; phytoplankton and zooplankton. Here, phytoplankton is the single-celled plants capable of undergoing photosynthesis. But, zooplankton is the small animal forms that feed on phytoplankton. In addition to these, a third group called bacterioplankton contains bacteria. Furthermore, the size of plankton may vary, starting from the microscopic size into the much larger forms of zooplankton such as jellyfish. Meanwhile, pleuston is the plankton that lives on the surface of the water while nekton is the type of plankton that actively swim. 

Concerning their functions, the main function of phytoplankton is to synthesize nutrients, while zooplankton serves as the most suitable form of food for large animals. However, bacterioplankton recycles nutrients from the decomposing matter in the ocean, providing fundamental sources of nutrition for all ocean creatures.

Similarities Between Krill and Plankton  

• Krill and plankton are two types of small organisms that live in large water bodies.  
• They can be either drifting or floating in the water bodies.  
• Also,  they represent the bottom line of aquatic food chains.  
• Many large animals feed on them by filtering the water.   

Difference Between Krill and Plankton 

Definition 

Krill refer to small, shrimp-like, planktonic crustaceans of the open seas, eaten by several larger animals, specially the baleen whales. Meanwhile, plankton refers to the small and microscopic drifting or floating in the sea or freshwater, consisting chiefly of diatoms, protozoans, small crustaceans, and the eggs and the larval stages of large animals.  

Correspondence 

Krill are a type of zooplankton, while the two types of plankton include phytoplankton and zooplankton. 

Variation 

Krill belong to the Euphausiacea order with around 85 species while plankton belongs to a wide variety of species and orders. 

Size 

Krill resemble a tiny shrimp while plankton may vary in size from the microscopic level to the size of the largest plankton, the lion’s mane jellyfish that can reach up to 2.5 m. 

Propulsion 

Adult frill can swim against water currents while plankton are unable to swim against water currents.  

Importance in Aquatic Food Chains 

Krill are the dominant planktonic food source of marine mammals while plankton are the diverse collection of organisms that serve as a crucial source of food at the bottom line of food chains. 

Conclusion 

Krill are a type of small crustaceans that belong to the zooplankton. Also, they belong to the phylum Arthropoda. Featurewise, they have 2 small antennas, swimming legs, and eyes. Also, they form huge swarms in cold water. In comparison to krill, plankton is small. They are microscopic organisms that live in large water bodies. Of these, phytoplankton and zooplankton are two types of plankton, eaten by large animals in the water through filtration. However, zooplankton consumes phytoplankton. Meanwhile, phytoplankton are single-celled plants, undergoing photosynthesis. So, summing up; the main difference between krill and plankton is their type and importance in aquatic food chains. 

References:

1. “Antarctic Krill.” Australian Government, Department of the Environment and Energy, Australian Antarctic Division, 17 Oct. 2019, Available Here.
2. “Zooplankton.” MarineBio, MarineBio Conservation Society, 8 June 2019, Available Here.

Image Courtesy:

1. “Krillanatomykils” By Uwe Kils – english wikipedia (CC BY-SA 3.0) via Commons Wikimedia   
2. “Tomopteriskils” By uwe kils – Own work (CC BY-SA 3.0) via Commons Wikimedia