Divergent trophic responses of sympatric penguin species to historic anthropogenic exploitation and recent climate change

Abstract

The Southern Ocean is in an era of significant change. Historic overharvesting of marine mammals and recent climatic warming have cascading impacts on resource availability and, in turn, ecosystem structure and function. We examined trophic responses of sympatric chinstrap (Pygoscelis antarctica) and gentoo (Pygoscelis papua) penguins to nearly 100 y of shared environmental change in the Antarctic Peninsula region using compound-specific stable isotope analyses of museum specimens. A century ago, gentoo penguins fed almost exclusively on low-trophic level prey, such as krill, during the peak of historic overexploitation of marine mammals, which was hypothesized to have resulted in a krill surplus. In the last 40 y, gentoo penguin trophic position has increased a full level as krill declined in response to recent climate change, increased competition from recovering marine mammal populations, and the development of a commercial krill fishery. A shifting isotopic baseline supporting gentoo penguins suggests a concurrent increase in coastal productivity over this time. In contrast, chinstrap penguins exhibited no change in trophic position, despite variation in krill availability over the past century. The specialized foraging niche of chinstrap penguins likely renders them more sensitive to changes in krill availability, relative to gentoo penguins, as evinced by their declining population trends in the Antarctic Peninsula over the past 40 y. Over the next century, similarly divergent trophic and population responses are likely to occur among Antarctic krill predators if climate change and other anthropogenic impacts continue to favor generalist over specialist species.

Changing circumpolar distributions and isoscapes of Antarctic krill: Indo‐Pacific habitat refuges counter long‐term degradation of the Atlantic sector

“…Long‐term warming, sea ice decline and climatically‐induced reduction in recruitment have been linked to declines in the SW Atlantic krill stock (Loeb et al 1997; Atkinson et al 2004) and its contraction southward toward the Antarctic continent (Atkinson et al 2019). Shifts in the dominance of krill compared to other zooplankton taxa such as salps are suggested to be having major consequences for krill‐dependent predators and food webs of the Atlantic sector (Huang et al 2011; Trivelpiece et al 2011; McMahon et al 2019). By contrast, however, other studies suggest relative stability of the krill stock (Fielding et al 2014; Cox et al 2018; Kinzey et al 2018).…”

Update on the global abundance and distribution of breeding Gentoo Penguins (Pygoscelis papua)

“…While the drivers of decline for Adélie and Chinstrap Penguins are debated (Forcada and Trathan 2009;Trivelpiece et al 2011;Lynch et al 2012) there is considerable evidence that Gentoo Penguin life history provides some relative advantages. In particular, Gentoo Penguins have more flexibility in diet, foraging behavior, and breeding phenology, which suggests they may be more resilient to environmental change and better able to colonize newly exposed territory (Lynch et al 2011;Masello et al 2017;McMahon 2019). Moreover, Gentoo Penguins, unlike their congeners, can relay if the brood is lost early during incubation (Bost and Clobert 1992) benefit in the ability to buffer population growth from early season events.…”

“…These trends stand in stark contrast to their sister species, the Adélie Penguin (P. adeliae) and the Chinstrap Penguin (P. antarcticus), which have experienced considerable population declines on the Western Antarctic Peninsula (WAP), the principle drivers of which are still being debated (Forcada and Trathan 2009;Trivelpiece et al 2011;Lynch et al 2012). Current hypotheses for population increases and range expansion of Gentoo Penguins in this region include plasticity in their breeding phenology (Lynch et al 2011), generalist foraging strategies and a flexible trophic niche (Polito et al 2015;Herman et al 2017;McMahon et al 2019), and breeding habitat preferences (Cimino et al 2013) vis a vis warming temperatures and declines of sea ice (Stammerjohn et al 2008) throughout the waters around the WAP.…”

Atlantic walrus signal latitudinal differences in the long-term decline of sea ice-derived carbon to benthic fauna in the Canadian Arctic

“…Student t-tests were used to determine a significant difference in δ 13 C Phe , δ 15 N Phe and sea ice-derived carbon between 1996 versus 2006 for individuals collected in Jones Sound. There are several trophic position (TP) equations derived from compound-specific stable isotope analysis of individual amino acids that provide a range in trophic position estimates for marine mammals and seabirds [38,39]. Given the high amount of variation in trophic discrimination factors between glutamic acid and phenylalanine (TDF Glu-Phe ) related to a species' mode of nitrogen excretion and diet quality [27], multi-TDF equations are considered more accurate and can improve trophic position estimates of consumers compared to single, step-wise TDF equations [30,31,39], and provide further support for a scaled TDF and trophic level framework [40].…”