Antarctic krill are small crustaceans inhabiting the Southern Ocean. These shrimp-like creatures exist in immense numbers, forming some of the largest animal aggregations on Earth. While individually small, their collective biomass is substantial, estimated at 400-500 million metric tons. Their abundance makes them a subject of considerable interest in marine science.
Meet the Antarctic Krill
Antarctic krill (Euphausia superba) are transparent with a reddish tinge. They grow to about 6 centimeters (2.4 inches) in length and weigh up to 2 grams (0.071 ounces). Their large black eyes are a notable feature, and their digestive system often appears green due to their diet.
These crustaceans live in the cold waters around Antarctica, forming massive swarms. These aggregations can be incredibly dense, sometimes reaching 10,000 to 30,000 individuals per cubic meter. Some swarms are so vast they can extend for tens of kilometers wide and over a hundred meters deep, even being visible from space.
Antarctic krill primarily feed on microscopic phytoplankton, especially small diatoms, which they filter from the water using a specialized feeding basket. In winter, when phytoplankton are less abundant, krill can also consume algae growing on the underside of sea ice, detritus on the seafloor, or other small zooplankton.
Important Role in the Ecosystem
Antarctic krill hold an important position in the Southern Ocean’s food web, serving as a primary link between microscopic plant life and larger marine animals. Their immense biomass transforms phytoplankton energy into a form accessible to many predators. This role designates them a keystone species in the Antarctic ecosystem.
Many Antarctic animals depend on krill. Whales, including blue, humpback, fin, and minke whales, consume vast quantities, with blue whales relying on them as their primary diet. Seals, such as crabeater, leopard, Weddell, and fur seals, also eat krill; crabeater seals, for instance, have specialized teeth to sieve krill from the water.
Penguins, including Adélie, chinstrap, macaroni, and emperor penguins, are major consumers of krill. Various seabirds, fish, and squid also depend on krill, directly or indirectly, for their survival in the Antarctic climate. The abundance of krill directly supports the rich biodiversity found in this polar region.
Challenges Facing Krill Populations
Antarctic krill populations face multiple pressures, with climate change being a primary concern. Rising ocean temperatures in the Southern Ocean disrupt krill growth and reduce their suitable habitat. Projections indicate a potential loss of 30% of their suitable habitat this century under warming scenarios.
Reduced sea ice is another direct impact of climate change on krill. Sea ice provides breeding grounds and a habitat for algae, a food source for krill, especially during winter months. The decline in sea ice cover therefore affects krill’s life cycle and food availability.
Ocean acidification, caused by increased ocean absorption of carbon dioxide, poses another threat. Research suggests that increased acidity negatively impacts krill egg hatching rates and development. Scientists predict that if carbon dioxide emissions are not mitigated, the Southern Ocean krill population could experience a significant decline, potentially collapsing by 2300, with far-reaching consequences for the entire ecosystem.
Krill and Human Activities
Human activities interact with Antarctic krill primarily through commercial fishing. Krill are harvested to produce krill oil supplements, valued for their omega-3 fatty acids, and for aquaculture feed. The demand for these products has led to an increase in krill catches over the past decade.
Managing this fishery sustainably is important to ensure the health of the Antarctic ecosystem. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), an international body of 26 nations, regulates krill fishing. CCAMLR employs an ecosystem-based approach, setting precautionary catch limits, such as a “Trigger Level” of approximately 1% of the estimated krill biomass in fishing areas.
This precautionary limit aims to leave enough krill for a healthy breeding population and their predators. While total krill catches have increased, they have historically remained below CCAMLR’s overall catch limits. Continued scientific monitoring and adherence to these international management efforts are necessary to balance human use with conservation.