Antarctic krill’s swarming biomass feeds an entire ocean
Krill are small marine crustaceans of order Euphausiacea, found in every ocean. The name is Norwegian for fish fry. Near the food web’s base, they graze phytoplankton and sustain whales, seals, penguins, and fish—Antarctic krill alone may total around 379 million tonnes of biomass.
Euphausiidae holds ten genera and eighty-five species (Euphausia the largest genus with thirty-one); Bentheuphausiidae’s single deep-water Bentheuphausia amblyops lives below 1,000 m and is considered the most primitive living krill. Commercial targets include Antarctic (E. superba), Pacific (E. pacifica), and Northern krill (Meganyctiphanes norvegica). Global catch runs about 150,000–200,000 tonnes yearly, mostly Scotia Sea, for aquaculture feeds, bait, pharmaceuticals, and food—okiami in Japan, bagoong paste in the Philippines. Molecular clocks put Euphausiidae’s last common ancestor near 130 million years ago.
Most adults are 1–2 cm; giants such as Thysanopoda cornuta reach 6–15 cm. Transparent exoskeletons, compound eyes, and externally visible gills distinguish them from true shrimp. Five pairs of swimming pleopods resemble lobster swimmerets, yet thoracic legs serve feeding and grooming, so they are not decapods. Except B. amblyops, species glow via rotatable photophores—likely diet-derived luciferin—for mating, schooling, or counter-illumination.
Filter-feeding thoracopod combs sieve diatoms; some species hunt copepods. Daily vertical migrations feed night predators at the surface and day hunters deeper—acoustic tracks to 400 m. In the Southern Ocean, E. superba often stays in the upper 100 m while ice krill can occur far deeper. A 1998 Bering Sea coccolithophore bloom crashed diatoms, Pacific krill, shearwaters, and that season’s salmon spawning—showing how tightly higher life depends on these shrimps. Blue whales and other baleen whales rely on these dense swarms as staples.
Climate change adds pressure, and early work suggests krill can shred microplastics under 5 mm into still smaller fragments.
Source: Krill
