What Are Antarctic Krill?
Antarctic krill, or Euphausia superba, reside in the pristine waters of the Southern Ocean and are the largest of 85 known species of krill. On average, these zooplankton invertebrates live between 5 and 7 years, though they can survive for as long as 10 years. Despite their small size (1-2 g per individual), the total Antarctic krill biomass is estimated to weigh around 500 million tons—which is roughly equivalent to the total estimated weight of the human population.
At a mere 5-6 cm long, Antarctic krill are small shrimp-like crustaceans. Krill are characterized by their large black eyes full of astaxanthin, semi-transparent bodies, soft exoskeletons, and a reddish tinge. Their visible digestive systems often appear bright green, which is the same color as the chlorophyll-rich food they consume. They also have several pairs of legs to keep them swimming along.
Antarctic krill are primarily herbivorous, though they are known to occasionally dine on other small zooplankton. In summer, they feed on phytoplankton, or microscopic unicellular plants that linger near the ocean’s surface and absorb carbon dioxide produced by sunlight.
In winter, limited exposure to sunlight creates a nutrient-poor environment at the ocean’s surface. When food production is low, either krill thrive on the ice algae communities that grow along the underside of Antarctic ice packs or will fast. Fortunately for these tough creatures, they can survive for up to 200 days without eating, although they might shrink loosing protein.
The lipid content of Omega-3 EPA or DHA in Antarctic krill can vary depending on the main micro-algae present in the environment on which it is feeding. If diatoms, it will be higher in EPA; if flagellates, it will be higher in DHA.
To better protect themselves against predators, krill constantly migrate about the ocean in dense swarms. By day, they fall down the water column and dwell near the ocean floor. By night, they rise up the water column toward the surface in search of food. Depending on the time of year, krill can grow swarms so dense and widespread that areas of the ocean’s surface turn pinkish-red.
Krill & The Food Chain
Antarctic krill are found at the bottom of the food chain. Though small in size, they are a primary food source for many marine animals, including squid, seals, penguins, water birds, fish and other marine life. In fact, even gigantic baleen whales dine on krill. While floating in swarms may protect krill against smaller predators, this activity is no match against whales, who scoop up large portions and trap them with filters called baleen plates. Krill fisheries capture only about 0.02% of the total biomass estimate each year which doesn’t come remotely close to affecting these marine animals.
Krill are often referred to as light-shrimp because they can emit light, produced by bioluminescent organs. These organs are located on various parts of the individual krill’s body (the eyestalk, thoracic legs, the tail or telson). The light organs emit a yellow-green light periodically, for up to 2–3 s. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles.
The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill’s shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in mating or schooling at night. The krill’s bioluminescent organs contain several fluorescent substances.
About the author
Luc Rainville obtained his Bachelor’s degree in biological sciences at Université de Montréal and his Master’s degree in sciences (biological oceanography) at Université Laval. He also completed his Doctorate in oceanography, at McGill University. He currently holds the position of Scientific Director for Neptune. As a krill and other marine species specialist, Luc Rainville uses his extensive knowledge in this field to develop new biomasses for Neptune. He was one of the founders of the company.