The Arctic Ocean is a harsh, seasonally extreme environment where life depends on the efficient transfer of energy from the base of the food web. Zooplankton are tiny animals floating in the water column that serve as the primary link converting energy from microscopic marine plants into a consumable form. These small organisms, dominated by lipid-rich copepods and krill, fuel the entire ecosystem. They connect primary producers like phytoplankton and ice algae to the region’s iconic fish, seabirds, and marine mammals.
Small Fish and Invertebrate Consumers
Zooplankton are consumed by a vast array of smaller organisms that form a critical intermediate layer in the food web. The Arctic Cod (Boreogadus saida) is a prime example, often called a nodal species because it links zooplankton to many larger predators. This small fish feeds extensively on copepods, especially the fat-storing Calanus glacialis, and on small crustaceans like amphipods. The Arctic Cod’s ability to thrive on this diet makes it a concentrated source of energy for seals and seabirds.
Predatory invertebrates also consume zooplankton directly. Chaetognaths, commonly known as arrow worms, are transparent, dart-shaped predators that ambush and consume copepods and other smaller zooplankton. Various species of amphipods, which are small, shrimp-like crustaceans, also graze on copepods or scavenge. These smaller consumers efficiently harvest zooplankton blooms and distribute that energy to larger hunters.
Seabirds that Hunt Zooplankton
Avian predators rely heavily on localized, dense patches of zooplankton and the small fish that feed on them. The Dovekie, or Little Auk (Alle alle), is the most dedicated zooplankton feeder among Arctic seabirds, subsisting almost exclusively on calanoid copepods. These small birds employ specialized diving techniques to forage in the upper water layers where their prey aggregates.
The enormous wintering population of Dovekies, estimated to be in the tens of millions, consumes thousands of tonnes of copepods daily. Other species like Thick-billed Murres and various Auklets also target zooplankton, particularly larger crustaceans and juvenile Arctic Cod. Their population health and breeding success are directly tied to the availability and nutritional quality of these energy-dense patches.
Marine Mammals as Primary Zooplankton Feeders
Marine mammals represent the largest-scale consumers of zooplankton, relying on the volume and high lipid content of their prey to sustain massive body sizes. Baleen whales are the most prominent zooplankton filter feeders. Bowhead Whales (Balaena mysticetus) and Fin Whales employ their bristle-like baleen plates to strain dense swarms of euphausiids (krill) and copepods from the water.
These megafauna require immense quantities of zooplankton to build the thick blubber layers needed for insulation and energy reserves. The Bowhead Whale can filter-feed for many hours a day during the feeding season, consuming tons of food to sustain its long life. The lipid-rich nature of Arctic zooplankton, which store high levels of energy, makes them an ideal prey item for these large filter feeders.
Seals also consume zooplankton, especially when younger. Harp Seals (Pagophilus groenlandicus) and Ringed Seals (Pusa hispida) consume zooplankton like krill and copepods, particularly during their juvenile stages. As they mature, their diet shifts to include small fish, but zooplankton remains a foundational part of their energy intake. The abundance of zooplankton is directly reflected in the health and reproductive success of these seals, which are a primary food source for the Polar Bear.
The Role of Zooplankton in Arctic Energy Transfer
Zooplankton are the fundamental mechanism for transferring solar energy up the Arctic food chain. They graze on phytoplankton and ice algae, which capture sunlight to produce fatty acids, notably Omega-3s. By consuming these primary producers, zooplankton package this energy into lipid-rich bodies that are readily available to predators.
This process ensures that the energy derived from the brief summer burst of primary production is efficiently distributed to all higher trophic levels, supporting everything from forage fish to the largest whales. The stability of the Arctic marine ecosystem is dependent on the health and timing of zooplankton reproduction and growth.
Changes in sea ice dynamics, such as earlier melt, can disrupt the timing of these vital blooms. This threatens the synchronized energy transfer that sustains all Arctic life.