Abstract
Antarctic seals and seabirds are strongly dependent on sea-ice cover to complete their life history. In polar ecosystems, sea ice provides a habitat for ice-associated diatoms that ensures a substantial production of organic matter. Recent studies have presented the potential of highly branched isoprenoids (HBIs) for tracing carbon flows from ice algae to higher-trophic-level organisms. However, to our knowledge, this new method has never been applied to sub-Antarctic species and Antarctic seals. Moreover, seasonal variations in HBI levels have never been investigated in Antarctic predators, despite a likely shift in food source from ice-derived to pelagic organic matter after sea-ice retreat. In the present study, we described HBI levels in a community of seabirds and seals breeding in Adelie Land, Antarctica. We then validated that sub-Antarctic seabirds had lower levels of diene, a HBI of sea-ice diatom origin, and higher levels of triene, a HBI of phytoplanktonic origin, compared with Antarctic seabirds. Finally, we explored temporal changes in HBI levels after the ice break up in summer. The level of diene relative to triene in Adelie penguin chicks increased and then declined during the breeding season, which was consistent with the short and intense proliferation of sea-ice algae in spring, followed by the pelagic phytoplankton bloom in summer. HBI biomarkers in Antarctic seabirds and seals thus indicate a shift from ice-algal derived organic matter to a pelagic carbon source during the summer breeding season.
Highlights
Antarctic top predators, such as seals and seabirds, are strongly dependent on sea-ice cover to complete their life history (Barbraud & Weimerskirch 2001, Siniff et al 2008, Forcada et al 2012)
We described highly branched isoprenoids (HBIs) levels in a community of seabirds and seals breeding in Adélie Land, Antarctica
D/T ratios were 7 times higher in eggs of the Adélie penguin compared with the cape petrel; 1.5 times higher in the Adélie penguin compared with the snow petrel; and 4.5 times higher in the snow petrel compared with the cape petrel
Summary
Antarctic top predators, such as seals and seabirds, are strongly dependent on sea-ice cover to complete their life history (Barbraud & Weimerskirch 2001, Siniff et al 2008, Forcada et al 2012). One may predict that the relative contribution of ice-derived organic matter for Antarctic top predators reaches a peak in late spring and early summer. This seasonal shift in carbon source has been poorly investigated due to the lack of appropriate and specific ice proxies. A new set of diatom markers known as highly branched isoprenoids (HBIs) could be good candidates for evaluating the seasonal importance of ice algal-derived organic matter in polar marine consumers (Brown et al 2013a,b, Goutte et al 2013).
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