The Arctic Cod (Boreogadus saida) is a foundational species in the cold, complex marine environment of the Arctic Ocean. This small fish thrives near sea ice, navigating the water column and feeding on the abundant microscopic life that forms the base of the food web. Understanding the Arctic Cod’s diet is important because its feeding patterns directly impact the health of the entire ecosystem. Krill are a well-known food source in other polar regions, leading to the question of whether this cod consumes them. This article explores the Arctic Cod’s relationship with krill and the other organisms that make up its primary diet.
Krill’s Place in the Arctic Cod Diet
Arctic Cod do consume krill (euphausiids), but they are generally not the most significant part of their diet. The inclusion of krill is opportunistic and varies greatly depending on the season and the cod schools’ geographic location. Krill can become a more important food item in certain areas where other prey species are less available. This makes krill a variable component rather than a constant staple.
Juvenile Arctic Cod often prefer smaller prey items compared to the larger euphausiids that make up krill swarms. While Atlantic Cod juveniles may have a diet dominated by krill, their Arctic Cod counterparts often focus on smaller crustaceans. The presence of krill in the diet underscores the Arctic Cod’s nature as a generalist feeder. This flexibility allows the species to adapt its consumption to the most readily available prey.
A Broader Menu of Arctic Prey
The majority of the Arctic Cod’s diet is composed of smaller, abundant zooplankton, which are tiny animals that drift in the water column. The most common prey items are copepods, particularly species of the genus Calanus. These small, fat-rich crustaceans form dense populations and are easily accessible to the schooling cod. Arctic Cod also feed heavily on amphipods, another group of small crustaceans, including hyperiid and gammarid species.
These smaller organisms, unlike the larger krill, provide the bulk of the energy transfer from the base of the food web to the fish. The cod’s small mouth size and tendency to form large schools enable it to efficiently filter-feed or “graze” on these massive zooplankton populations. The cod also consumes other small organisms, such as chaetognaths and mysids, demonstrating an adaptable feeding strategy that prioritizes plentiful food sources.
The Cod’s Central Role in Energy Transfer
Due to its efficient consumption of zooplankton, the Arctic Cod acts as an ecological link, transferring energy from the base of the food web to the top predators. The cod converts the energy stored in copepods and amphipods into a larger, accessible biomass. This process is efficient because the Arctic Cod accumulates high concentrations of lipids, making it an energy-rich prey item.
Researchers estimate that this fish funnels more than 70% of the energy derived from zooplankton to higher trophic levels within the Arctic ecosystem. This energy pathway sustains many of the region’s marine mammals and seabirds. Predators that rely heavily on the Arctic Cod include ringed seals, beluga whales, narwhals, and several species of seabirds. These seabirds include thick-billed murres and ivory gulls. The continued health and abundance of the Arctic Cod population is directly tied to the survival of these Arctic species.