The food chain of the Beaufort Sea is relatively simple: It starts with phytoplankton and epontic algae (single-cell algae associated with the lower interface of sea ice), which provide energy to zooplankton, and epontic and coastal amphipods. The latter serve as a food for seabirds and fish, primarily as polar cod and Arctic char. Polar cod is a major food of Arctic char, beluga, narwhal, seabirds and seals, which are dominated by the bearded seal ("Erignatus barbatus") and ringed seal ("Pusa hispida"). Bearded seal and walrus also feed on benthic invertebrates. On top of the food pyramid stands polar bear, which feeds primarily on seals, but also on any large marine mammals when it has a chance, such as carcasses and whales trapped in ice fields.