Euphausiids, commonly known as krill, are small marine crustaceans found in vast numbers across all oceans. These tiny organisms form immense swarms, representing an enormous collective biomass. Their abundance makes them significant to marine ecosystems globally.
Defining Euphausiids
Euphausiids are marine crustaceans of the order Euphausiacea, with over 80 known species. Most are small, one to two centimeters long, though some deep-sea species reach 15 centimeters. Many krill species possess light-producing organs called photophores, enabling bioluminescence.
These shrimp-like creatures are found in all oceans, from coastal waters to the open sea. They are abundant in cold, nutrient-rich regions, like the Southern Ocean surrounding Antarctica. Krill are known for schooling, often forming dense swarms spanning kilometers and containing tens of thousands of individuals per cubic meter.
Ecological Significance
Krill hold a foundational position in marine food webs, linking primary producers and higher trophic levels. As filter feeders, most krill primarily consume microscopic phytoplankton, especially diatoms, which are single-celled algae. Some krill species also feed on zooplankton and fish larvae, demonstrating an omnivorous diet.
This diet allows krill to convert energy from these tiny plants into a form consumable by larger animals. Their immense biomass, estimated at hundreds of millions of metric tons for Antarctic krill alone, supports a wide array of marine life. Whales, seals, penguins, seabirds, and various fish species rely on krill as a primary food source.
For instance, giant blue whales feed almost exclusively on krill, consuming up to four tons daily. Krill also contribute to the ocean’s biological pump, transporting carbon from surface waters to the deep ocean through their feeding and excretion, influencing global carbon cycles.
Impacts of Environmental Change
Euphausiid populations face pressure from global environmental changes, especially climate change. Ocean warming directly affects krill growth rates, potentially reducing their overall biomass. Studies indicate warming waters have caused Antarctic krill distribution to contract southward by hundreds of kilometers since the 1920s, as krill adapt to colder conditions.
Ocean acidification, from increased carbon dioxide absorption by seawater, poses another threat. While adult krill show resilience due to specialized ion pumps, their eggs and embryos are susceptible, as acidification can inhibit shell formation and impact development. Loss of winter sea ice also impacts krill, especially in polar regions, by reducing their primary food source of ice algae and affecting larval survival and recruitment. Such disruptions to their life cycle and distribution can have cascading effects throughout the marine ecosystem, potentially reducing predator populations like penguins.
Human Interactions and Conservation
Human activities interact with krill populations primarily through commercial fishing. Krill are harvested on a large scale, mainly for their oil, used in dietary supplements, and as feed for aquaculture. The Southern Ocean, particularly “Area 48” near the Antarctic Peninsula, is a major fishing ground, with catches increasing in recent years.
To manage this fishery sustainably, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) sets precautionary catch limits. This international body, comprising 27 members, employs an ecosystem-based management approach considering krill predator needs. Current regulations aim to keep total catches below 1% of the estimated krill biomass in designated areas, ensuring enough krill remain for reproduction and for dependent animals. Observers are often present on fishing vessels, and advanced technologies like sonar and drones monitor populations and fishing activity, contributing to transparent and responsible practices.