The trophic link between squid and the emperor penguin Aptenodytes forsteri at Pointe Geologie, Antarctica

Cephalopod beaks retrieved from stomachs of dead emperor penguin chicks at Pointe Geologie, Terre Adelie, provide information on taxonomic and size composition of the penguin's squid diet, on the trophic range of the squid species preyed upon and on the fractional trophic impact of the penguin on the whole food web. Emperor penguins prey upon four squid species (Psychroteuthis glacialis, Kondakovia longimana, Gonatus antarcticus, Alluroteuthis antarcticus) and do not take squid larger than 480 mm mantle length. Larger squid live either below the penguin's diving range or are beyond its handling capacity. Nitrogen stable isotope ratios indicate that squids cover a range of about two trophic levels (2.5-8 parts per thousand delta N-15). The impact of the emperor penguin, however, concentrates on the upper part of this range, about 68% of its squid prey being > 6 parts per thousand delta N-15. The principal components of the emperor's diet, fish, krill and squid, differ distinctly in average trophic level. Consequently the trophic position of the emperor penguin changes accordingly with diet composition and may differ by almost one trophic level between different emperor penguin colonies.