Antarctic krill are small, shrimp-like crustaceans that inhabit the frigid waters of the Southern Ocean. Classified as zooplankton, the Antarctic species, Euphausia superba, is unique due to its immense collective mass. It boasts one of the largest single-species biomasses on the planet, estimated between 379 and 500 million metric tons. Their sheer abundance makes them an irreplaceable component of the Antarctic marine environment. Understanding the dynamics of this organism is central to assessing the stability and health of the entire ocean ecosystem.
The Foundation of the Antarctic Food Web
Krill occupy a foundational position in the Southern Ocean’s ecology, serving as the primary bridge between the most microscopic forms of life and the largest animals on Earth. They are prodigious grazers, feeding directly on minute phytoplankton, which are the primary producers that capture solar energy. By consuming phytoplankton, krill convert this energy into a highly nutritious, lipid-rich food source for a vast array of marine life.
The survival of numerous iconic Antarctic animals is directly tied to the availability of krill swarms. Baleen whales, including the massive blue whale, filter feed almost exclusively on krill during their time in the Southern Ocean. Seals also rely heavily on this crustacean, particularly the Crabeater seal, whose diet consists of an estimated 98% krill.
Penguins (Adelie, Chinstrap, and Gentoo species), seabirds, and fish all feed on krill. Their massive, dense swarms, which can reach up to 20 kilometers in length and contain millions of tonnes of animals, make them an accessible and energy-efficient meal for predators. Any significant fluctuation in krill populations sends destabilizing ripples up the entire food chain, directly affecting the reproductive success and overall population health of these higher-trophic organisms.
Krill’s Role in Carbon Cycling and Nutrient Flow
Beyond their function as a food source, krill participate in the ocean’s biogeochemical cycles. They are a major contributor to the “biological carbon pump,” a process that moves carbon from the atmosphere to the deep ocean. Krill consume phytoplankton, which have fixed atmospheric carbon dioxide through photosynthesis, and then process this carbon.
Their unique digestive system produces dense fecal pellets that are rich in carbon and sink rapidly through the water column. These pellets sink fast enough to escape immediate recycling near the surface, effectively transporting the carbon to the deep ocean floor. This process sequesters the carbon for potentially centuries, removing it from active exchange with the atmosphere.
Scientific research estimates that krill are responsible for storing at least 20 million metric tons of carbon in the deep ocean every year. This sequestered amount is comparable to the carbon stored annually by major coastal ecosystems like mangroves and salt marshes. Additionally, krill excrete dissolved nutrients like iron and nitrogen while grazing, which can stimulate the growth of more phytoplankton.
Environmental and Commercial Pressures on Krill
The stability of the krill population is increasingly threatened by two major human-driven pressures: climate change and concentrated commercial harvesting. Krill populations are highly sensitive to rising ocean temperatures and the resulting loss of sea ice habitat. Krill rely on the underside of seasonal winter sea ice as a crucial refuge from predators and as a primary feeding ground for the ice algae that sustain them during the colder months.
The rapid warming along the Antarctic Peninsula has led to a significant reduction in the extent and duration of this sea ice, which negatively affects krill recruitment and survival rates. Studies suggest that climate change may lower krill growth rates, ultimately resulting in a smaller total biomass available to the ecosystem. Ocean acidification, another consequence of increased atmospheric carbon dioxide absorption, also poses a threat by potentially reducing krill development and hatching rates.
Commercial fishing further complicates the situation, as krill are harvested primarily for use in aquaculture feed, omega-3 supplements, and pet food. Although the total commercial catch is a small fraction of the estimated total krill biomass, fishing efforts are heavily concentrated in a few biologically productive areas, particularly around the Antarctic Peninsula. This localized concentration creates “hotspots” of depletion, removing krill from the feeding grounds of seals, whales, and penguins, which can severely impact these dependent animal populations.
International Strategies for Krill Conservation
The international community manages the krill fishery through the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), established in 1982. CCAMLR operates under an ecosystem-based approach, which requires that fishing activities do not negatively affect the entire food web, especially species dependent on krill. This system employs a principle of precautionary management, setting limits well below the estimated sustainable yield to account for uncertainty in population estimates.
For the main fishing area (Area 48, which includes the Antarctic Peninsula and Scotia Sea), the total precautionary catch limit is set at 5.61 million tonnes, based on an estimated biomass of 60.3 million tonnes. However, a much lower trigger level of 620,000 tonnes currently governs the fishery, ensuring that catches remain highly constrained. This trigger level is a temporary measure designed to prevent the fishery from expanding until a more detailed management system is in place to spatially distribute the catch.
CCAMLR is actively working to refine its management by dividing the large fishing zones into smaller management units. The goal of these Small-Scale Management Units (SSMUs) is to better protect the foraging areas of land-based predators like penguins and seals from localized krill depletion. Through mandatory scientific observers on fishing vessels and the use of Vessel Monitoring Systems, CCAMLR aims to ensure that the krill population remains available to the Antarctic wildlife that depends on it.