The Antarctic krill, euphausia superba, are almost invisible to the naked eye. They only measure 2.3 inches (6.2 centimeters) in length, and weigh about 0.03 ounces (1 gram). Their bodies are divided into 3 sections, 2 of which are fused together (the head and thorax form the cephalothorax). Each section is then divided into individual segments, with many of them having a pair of appendages. The 3rd section of the Antarctic krill, the abdomen, has appendages on the end which flatten and form the tail fin (called a telson). An Antarctic krill’s body is mostly transparent in color, although they do have some bright red from small pigment spots.
The Antarctic krill has a wide distribution which includes the British Antarctic Territory, the waters surrounding South Georgia and the South Sandwich Islands, as well as the tip of South America and the Falkland Islands. Adults tend to be found in deeper waters while juveniles are closer to the surface of inshore waters, beneath the sea ice. Antarctic krill are also commonly found in large groups when surface currents bring them together. These large groups can cover an area as small as a few square feet (meters), to more than 62 square miles (100 square kilometers).
The diet of an Antarctic krill consists mainly of phytoplankton (microscopic aquatic plants that are suspended in the water). During the winter months however, it will eat a wide variety of things including zooplankton (microscopic animals that drift with the water movement), detritus (litter that is formed from fragments of dead material), and even its own eggs and larvae. Antarctic krill are an essential part of the food chain, and as such they have a wide variety of predators such as seals, whales (blue whales for example), penguins (such as the emperor penguin), and many types of fish.
Breeding season for the Antarctic krill mainly takes place during the summer. The male will produce tiny sperm packets which they will transfer to the reproductive organs of the female using its legs. The female will store the packets until she is ready to lay her eggs (up to 10,000), fully fertilized. The eggs are laid at the surface, and sink up to 6,561 feet (2000 meters) before hatching into the first of many larval stages called ‘nauplii.’ The nauplii begin migrating to the surface, going through its other larval stages until it finally becomes a juvenile Antarctic krill by the following spring. The likelihood of Antarctic maturity depends largely on how long the sea ice remains on the surface. As this provides protection for them, the longer it stays, the better chance they have a making it to adulthood.
Antarctic krill have been in decline over the last 30 years. Demand for krill meat and oil, as well as climate change have all played parts in their drop in numbers. There are steps being taken to help ensure that over-fishing of these creatures does not occur and that there is minimal impact to the local wildlife. Hopefully, such steps will help Antarctic krill recover from their current obstacles. After all, such a unique and critical species deserves to live and prosper for many years.
“Antarctic Krill (Euphausia Superba)” 17 April 2011
“Krill” 17 April 2011
“How do Krill Reproduce?” 17 April 2011