This Wildlife of the Week we ask you to name this tiny creature! Is it shrimp? Herring? Prawns? The massive swarm of tiny creatures in this photo is Krill! Krill is similar to shrimp in many ways, and is a favourite food item of many baleen whales. Rather than being defined as a single species, Krill is a general name used to describe multiple “Euphausiidae” and “Bentheuphasia” species worldwide, the Antarctic species being the largest. Though Krill may resemble fish, they are in fact a crustacean and thus an invertebrate (no backbone).
The impact of Krill might not be obvious when looking at their small size, but they are essential to the functioning and survival of major marine food webs. Read along below to learn more!
Krill might appear very similar to other ocean critters, but there are several scientific clues that set them apart. A Krill’s body is an orange/red color and partly see-through (translucent). They measure only a mere 1-2 cm long on average, but some have been recorded at over 6-15 cm! Like other crustaceans, Krill have a harder exoskeleton that protects their body. In Krill, the digestive system is also entirely visible to the naked eye.
Telling invertebrates apart can be a challenging business, but if you take notice of the different “segments” of an animal’s body, telling animals apart becomes slightly easier. Krill have 3 body segments, two of which are tightly combined, or fused. The Krill has two sets of appendages, one for swimming and one for feeding/ grooming, the latter attached to their tail. If you ever encounter a Krill, you might notice their large black eyes and obvious gills.
Krill, within its various species, is dispersed around the globe. There are various species that live along Canada’s coasts, and at least over 80 known species have been identified around the world. The most abundant species is the Antarctic krill. Krill live in the pelagic zone (open sea), but the ones that live in the deepest waters are the “Bentheuphasia” mentioned above. Krill perform amazing daily migrations, moving to shallow water to feed (less than 50m) during the day, before returning to deeper waters for protection from predators. This is a massive movement of biomass (organic material)!
Krill, as zooplankton, often feeds on phytoplankton. Phytoplankton is microscopic plant material, or algae, that photosynthesizes just like land plants do. Though many Krill are believed to solely feed on these primary producers, some may be carnivorous or omnivorous, and some Krill may even eat other Krill. They capture their food from the water using their “tail-legs” mentioned earlier. Their waste is beneficial to the marine food web and helps to circulate nutrients and organic materials.
Krill reproduce slightly differently depending on their own species. However, there are some commonalities that scientists have deduced. Generally, Krill will have a mating season that varies depending on ocean factors and species. Fertilized eggs may be carried by the female or be required to be independent in the ocean immediately. The eggs will develop into a larval form, which usually remain in deeper water until they become further developed. These larvae eventually make their way to the surface when their feeding appendages have developed to take advantage of the phytoplankton. Like a crab, Krill will also “shed” or “moult” their exoskeleton shell as they grow and develop into an adult.
Notice the “swarm” of Krill in the photo above; these swarms may also occur during mating events. A species known in British Columbia (Euphausiacea pacifica) spawns during the spring/early to mid summer and again in the fall.
Krill is an animal that supports countless species in the ocean and the healthy functioning of the ocean itself. They serve as a food source for penguins, whales, fish and seals. Some whales only feed on Krill! Interestingly enough, Krill’s digestion of phytoplankton allows other animals to receive the nutrients in a way that wouldn’t be possible otherwise when they consume the Krill. It has been hypothesized that climate-change induced decreases of Krill have been linked to some penguin species’ decreases.
Krill, as with many other marine organisms, are sensitive to changing ocean conditions brought upon by climate change. Melting sea ice brought upon by climate change reduces the cover that Krill and phytoplankton use for protection (from storms and predators). As well, there remains concern for overfishing from humans, due to the nutritional draw in Krill for human and animal food, as well as supplements. In the Pacific regions, studies have ascertained that many important schooling fish (e.g. Pacific hake, Pacific herring) depend on Krill. Larger species such as Humpback Whales have shown reflective movements in response to changing Krill abundances off of Vancouver Island. It is therefore critical that this little creature is in high, healthy abundance for future generations to come.
To test your “Krill” knowledge, try out some trivia below!
- True or False? Antarctic Krill biomass is more than the mass of humans globally. (ANS: True! At 379 million tonnes).
- Most Krill are bioluminescent via organs called _____ . (ANS: Photophores).
- The Krill is cold-blooded or warm-blooded? (ANS: Cold-blooded).
A common escape mechanism used by Krill is to swim backwards, in a quick, jet-like manner. This is referred to as what?
Article Authored By: Alexa D./ Five Star Whale Watching.
To learn more about Krill, check out our References below!
Helmenstine, A.M. 2019. “What is Krill?” ThoughtCo. Dotdash. Everything You Need to Know About Krill (thoughtco.com).
“Euphausiids (Krill)”. 2018. Department of Fisheries and Oceans Canada. Government of Canada. Euphausiids (Krill) (dfo-mpo.gc.ca).
“Krill.” Encyclopaedia Brittanica. Decapod | crustacean | Britannica.