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We evaluated annual and regional variation in the dietary niche of Pygoscelis penguins including the sea ice-obligate Adélie penguin ( Pygoscelis adeliae ), and sea ice-intolerant chinstrap ( Pygoscelis antarcticus ) and gentoo ( Pygoscelis papua ) penguins, three species that nest throughout the western Antarctic Peninsula (AP) to test the sea ice trophic interaction hypothesis , which posits that penguin breeding populations with divergent trends, i.e., declining or increasing, are reliant on differing food webs. Our study relies on values of naturally occurring carbon ( 13 C/ 12 C, δ 13 C) and nitrogen ( 15 N/ 14 N, δ 15 N) stable isotopes as integrated proxies of penguin food webs measured over three years at three different breeding colonies. At Anvers Island in the north, where reductions in sea ice and changes in breeding population trends among sympatric sea ice-obligate (Adélie) and sea ice-intolerant (chinstrap and gentoo) penguins have been most notable, our analyses show that all three species of Pygoscelis penguins became more similar isotopically over the reproductive period. By late chick-rearing at Anvers Island, crèched chicks at 5-weeks-old for all species occupied similar trophic positions. Isotopic mixing models indicated that the proportions of prey provisioned by adult penguins to 5-week-old chicks at Anvers Island were generally similar across species within years, consisting primarily of Antarctic krill ( Euphausia superba ). Crèched Adélie chicks had higher δ 13 C and δ 15 N values at Avian and Charcot Islands, southern breeding colonies where sea ice is more prominent and populations of Adélie penguins have increased or remain stable. Trophic position increased with latitude, while the proportions of prey provisioned by Adélie penguin adults to chicks at southern breeding colonies included species typical of high Antarctic marine food webs, especially crystal krill ( Euphausia crystallorophias ). A Bayesian metric for dietary niche width, standard ellipse area (SEA-B), indicated that Pygoscelis penguins with greater population changes in the north had more variability in dietary niche width than stable populations further south. Our results lend insight on marine food web drivers of Pygoscelis penguin reproduction at the regional scale and question the long-standing paradigm that Antarctic krill are the only food web component critical to penguin reproductive survival in this region of the Southern Ocean.
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Sea-ice and macrozooplankton distribution as determinants of top predator community structure in Antarctic winter
The Antarctic Peninsula marine ecosystem is highly productive, with large populations of commercially and ecologically important species including Antarctic krillEuphausia superba, Adélie penguinsPygoscelis adeliae, and crabeater sealsLobodon carcinophagus. The ecology of the peninsula is rapidly changing due to accelerating climate change and fishing pressure. Systematic ecosystem surveys have focused on austral spring and summer, leaving an information gap on winter ecosystem dynamics. Using data from 5 consecutive ecosystem surveys, we quantified the composition and distribution of winter predator communities and investigated the physical and biological influences on community structure. Seabirds and marine mammals clustered into 3 communities: an ice-associated community represented by Adélie penguins and crabeater seals; a diverse marginal ice zone community dominated by fur seals and several species of seabirds including 3 petrels, kelp gullsLarus dominicanus, and Antarctic ternsSterna vittata; and an open water community consisting of southern fulmarsFulmarus glacialoidesand 4 species of petrels. These communities were distributed along an environmental gradient ranging from ice-covered, cold, saline water to ice-free, warmer, and fresher water with greater chlorophyll concentrations. Predator communities were also associated with different communities of macrozooplankton: ice-associated predators with an extremely diverse assemblage of typically mesopelagic zooplankton; marginal ice zone predators with a community of large-bodied euphausiids (E. superba, E. crystallorophias); and open water predators with a community of small-bodied euphausiids (Thysanoessa macrura). Our synthesis of integrated winter predator and macrozooplankton communities relative to sea-ice concentration provides reference points for future ecosystem assessments within this rapidly changing region.
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- PAR ID:
- 10563368
- Editor(s):
- NA
- Publisher / Repository:
- Marine Ecology Progress Series
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 738
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 57 to 73
- Subject(s) / Keyword(s):
- Seabird · Marine mammal · Polar regions · Biogeography · Sea ice · Zooplankton · Krill
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps14609
