The capelin (Mallotus villosus) is a small, silver-colored forage fish belonging to the smelt family. This species thrives in the cold, nutrient-rich waters of the Arctic and subarctic regions, inhabiting areas like the North Atlantic, the Barents Sea, and the North Pacific. Capelin is one of the most abundant fish species in its habitat, establishing it as a foundational component of the marine ecosystem. Its importance is tied directly to its role as an energy conduit, transferring resources from the base of the food web to larger animals.
Capelin’s Diet: Consuming the Smallest Organisms
Capelin are classified as zooplanktivores, meaning their diet consists predominantly of tiny, free-floating animals known as zooplankton. The exact composition of their food intake changes based on the capelin’s size, age, and geographical location. Larval and juvenile capelin typically consume smaller prey, focusing primarily on various species of copepods.
The most common prey species include large, energy-rich copepods such as Calanus finmarchicus and Calanus hyperboreus. As capelin grow larger, they shift their diet toward bigger organisms to meet increasing energy demands. Adult capelin incorporate larger crustaceans like euphausiids (krill) and various amphipods.
For example, in the Barents Sea, larger capelin exhibit a pronounced shift from copepods to euphausiids, which become the largest contributor to their diet by weight. Conversely, capelin populations off the coast of Newfoundland often show less of a dramatic shift, with copepods remaining a dominant food source for most age groups. This adaptability allows the capelin to efficiently graze on the most abundant plankton available in their specific environment.
Ecological Role as a Primary Link
The capelin’s specialized diet gives it an outsized role in the cold-water food webs it inhabits. This fish serves as a primary trophic link, converting the energy stored in microscopic zooplankton into a body size accessible to a wide range of larger predators. The capelin population is often described as the “waist” in a “wasp-waist” food web structure, where a single intermediate species dictates the energy flow between lower and upper trophic levels.
By consuming massive quantities of zooplankton, capelin effectively accumulate and concentrate energy from the initial stages of the food chain. Capelin act as the biological intermediary, packaging low-trophic-level energy into dense, fatty, and easily digestible bundles. This process is important because most large, warm-blooded predators cannot efficiently feed directly on the scattered, tiny plankton.
An adult capelin returning from summer feeding can increase its fat content from about 4% up to 15–20% of its body weight. This high-efficiency energy transfer supports the entire structure of the northern marine ecosystem. The abundance of capelin directly influences the health and reproductive success of the marine megafauna that depend on this energy source.
Widespread Importance to Marine Predators
The capelin’s central position as an energy link makes it a foundational prey item for a vast number of higher-trophic-level species, including fish, marine mammals, and seabirds. Several commercially important finfish rely heavily on capelin as a primary food source:
- Atlantic Cod (often comprising almost 50% of its total diet)
- Haddock
- Greenland Halibut
- Turbot
Marine mammals also target capelin, particularly during their mass spawning migrations when the fish are concentrated. Harp Seals consume capelin, and their diet can include a wide range of prey depending on availability. Various whale species, including Minke whales and Humpback whales, feed extensively on capelin schools.
Seabirds such as Atlantic Puffins, Murres, and Guillemots are highly dependent on capelin for feeding their chicks, which require the high-fat content for rapid growth. The availability of capelin is a strong predictor of breeding success for these avian predators.
Capelin population crashes, such as those that occurred in the early 1990s, have been linked to dramatic declines in the condition and reproductive rates of these predator populations. When capelin stocks decline, the negative effects propagate upward, causing nutritional stress and reduced survival rates among seals, seabirds, and predatory fish. This extensive reliance across multiple trophic levels underscores the capelin’s role as a biological keystone species in the northern marine environment.