Adelie penguin diet composition, secondary prey items, 1991 - present.

• Main Authors: LTER, Palmer Station Antarctica, Fraser, William
• Format: Dataset
• Language: English
• Published: Environmental Data Initiative 2020
• Subjects: Antarctic; Adelie penguin; Antarc*; Sea ice
• Online Access: https://dx.doi.org/10.6073/pasta/7f02381b7c2d6d68b5642f4496117812; https://portal.edirepository.org/nis/mapbrowse?packageid=knb-lter-pal.98.6

The fundamental long-term objective of the seabird component of the Palmer LTER (PAL) has been to identify and understand the mechanistic processes that regulate the mean fitness (population growth rate) of regional penguin populations. Two hypotheses have guided this research, with one suggesting that population mean fitness is best explained by changes in regional krill biomass, and the other proposing that long-term changes in sea ice affects mean fitness by tipping the balance in favor of one species over another in accordance with species-specific evolved life history affinities to sea ice. Although these hypotheses are not mutually exclusive, current evidence in the PAL region tends to favor the latter over the former. Since the inception of PAL, Adélie penguin populations have effectively collapsed, while those of gentoo and chinstrap penguins have increased dramatically, trends that are spatially and temporally coherent with decreasing regional sea ice duration. Adélie penguins are an ice-obligate polar species whose life history is intimately linked to the presence of sea ice, while chinstrap and gentoo penguins are ice-intolerant species whose life histories evolved in the sub-Antarctic, where sea ice is a less permanent feature of the marine ecosystem. In contrast, although krill constitute the most important component of the summer diets by mass of these three penguin species, changes in PAL krill abundances have exhibited no long-term trends, and thus fail to explain the divergent patterns in penguin populations evident in our time series. Besides krill and fish, a number of secondary prey items (see DIET) can be found in Adélie penguin diets, including octopus, squid, amphipods, mysid shrimp, limpets and small clams. One or more of these prey types may occur frequently in the samples, but very rarely in abundance, hence recorded metrics are limited to detailing the number of specimens observed and obtaining weights if warranted by the sample size. One exception concerns squid and octopus beaks, which like fish otoliths can be identified to species and the size and mass of individuals reconstituted based on regressions that use beak length to determine relational metrics. Like otoliths, beaks are also processed by experts outside PAL (see FISH), hence similar time lags exist in database integration. What role these less abundant prey items have in Adélie penguin diets is unknown, but paleoecological evidence suggests that squid in particular were once consumed much more frequently in the PAL region than they are now.