Trophic interactions and variation in reproductive performance within a community of Antarctic penguins (genus Pygoscelis)

The southwestern Atlantic sector of the Southern Ocean, including the Bellingshausen Sea west of the Antarctica Peninsula (AP), is now strongly influenced by ocean-climate warming. Over recent decades, this region has experienced more frequent El Niño-Southern Oscillation and positive Southern Annular Mode (SAM) events, with SAM having direct anthropogenic linkages to ozone depletion. These climate phases are coupled with physical oceanographic forcing of relatively warm water derived from the Antarctic Circumpolar Current onto the continental shelf, delivering oceanic heat and influencing sea-surface temperature variability. Average winter air temperature has increased 6°C in association with a severe reduction in regional winter sea-ice formation, particularly within the northern sector of the western AP. Marine community responses to regional warming are now evident. Especially marked are breeding population responses by Pygoscelis penguins including the sea ice-obligate Adélie penguin (P. adeliae), in addition to the sea ice-intolerant chinstrap (P. antarctica) and gentoo (P. papua) penguins, all of which are demonstrating pole-ward shifts in bio-geographic range mediated by environmental effects on demographic parameters. Using data collected over the 2008-2010 austral summers, we examine nutritional correlates of within and among species variation in individual reproductive performance of Pygoscelis penguins nesting near Anvers Island; an ecotone now shifting from a cold, dry polar climate to a warm, moist sub-Antarctic system. Also, we consider latitudinal variation in reproductive performance among Adélie penguins nesting at Anvers Island, as well as 400 km south at Avian Island and 700 km south at Charcot Island, regions where sea ice remains a prominent physical feature. Analyses utilize naturally occurring ratios of carbon (delta¹³C) and nitrogen (delta¹⁵N) stable isotopes as proxies of marine trophic structure. Using information-theoretic methods, (1) delta¹³C and delta¹⁵N signatures of red blood cells (RBC) obtained from pairs of adults at the one-egg stage are coupled with data of body condition to examine nutritional correlates of primary reproductive effort. (2) RBC isotope signatures of penguin chicks at day 5, 15 and 5 weeks into chick rearing, also coupled with body condition data, are used to examine nutritional correlates of secondary reproductive effort. Finally, (3) we develop models of latitudinal variation in marine trophic structure.