A predator's perspective on causal links between climate change, physical forcing and ecosystem response

Abstract

ABSTRACT:The mechanisms by which variability in sea ice cover and its effects on the demography of the Antarctic krill Euphausia superba cascade to other ecosystem components such as apex predators remain poorly understood at all spatial and temporal scales, yet these interactions are essential for understanding causal links between climate change, ecosystem response and resource monitoring and management in the Southern Ocean. To address some of these issues, we examined the longterm foraging responses of Adélie penguins Pygoscelis adeliae near Palmer Station, western Antarctic Peninsula, in relation to ice-induced changes in krill recruitment and availability. Our results suggest that (1) there is a direct, causal relationship between variability in ice cover, krill recruitment, prey availability and predator foraging ecology, (2) regional patterns and trends detected in this study are consistent with similar observations in areas as far north as South Georgia, and (3) largescale forcing associated with the Antarctic Circumpolar Wave may be governing ecological interactions between ice, krill and their predators in the western Antarctic Peninsula and Scotia Sea regions. Another implication of our analyses is that during the last 2 decades in particular, krill populations have been sustained by strong age classes that emerge episodically every 4 to 5 yr. This raises the possibility that cohort senescence has become an additional ecosystem stressor in an environment where ice conditions conducive to good krill recruitment are deteriorating due to climate warming. In exploring these interactions, our results suggest that at least 1 'senescence event' has already occurred in the western Antarctic Peninsula region, and it accounts for significant coherent decreases in krill abundance, predator populations and predator foraging and breeding performance. We propose that krill longevity should be incorporated into models that seek to identify and understand causal links between climate change, physical forcing and ecosystem response in the western Antarctic Peninsula region.

Contrasting population changes in sympatric penguin species in association with climate warming

“…Persistent climate anomalies reducing the winter/spring sea ice extent appear to affect the recruitment and biomass of the krill exploited by penguins (see also Wilson et al, 2001;Fraser & Hoffmann, 2003); penguin population responses are also consistent with the duration of the anomalies that affect krill; these usually become manifest during the breeding season although they may operate before arrival. For example, impacts upon the number of breeding pairs could result from interactions that affect survival and/or foraging success over the winter period prior to the breeding season (Trathan et al, 1996); this may act over a number of weeks (or months) to impact upon body condition and subsequent ability to breed.…”

“…Adélie penguins at King George Island and Anvers Island, which are not far from Palmer station, had negative population changes in 1991 and 1995 (Fraser & Patterson, 1997;Trivelpiece & Trivelpiece, 2001). These population downturns apparently related to low krill abundance and sea ice (Fraser & Hoffmann, 2003) and they were concurrent with population downturns of chinstrap and Adélie penguins at Signy Island. Further research on the environmental consequences for chinstrap penguins at Palmer Station would help understand the common effects of global climate variability on penguin population changes.…”

“…A study from 1987 to 1997 near Palmer Station, Anvers Island, western Antarctic Peninsula, related years of low krill abundance and poor Adélie penguin performance with similar sea ice cycles (cf. Fraser & Hoffmann, 2003); in particular, during seasons 1990/1991 and 1994/1995, which were also poor seasons at Signy Island (Fig. 3).…”

“…This low krill supply correlated with low krill densities at Elephant Island (cf. Fraser & Hoffmann, 2003), situated 642 km NE of Palmer Station and 498 km W of Signy Island. Therefore, these low krill densities concurrent with sea ice anomalies at the South Orkneys (Fig.…”

Adélie penguin (Pygoscelis adeliae) survival rates and their relationship to environmental indices in the South Shetland Islands, Antarctica

“…Monitoring data in the WAP region support that expectation (Hinke et al 2007;Lynch et al 2008). In particular, reductions in Adélie penguin population size and recruitment to the breeding population have been correlated with variation in winter sea ice extent and krill demography throughout their circumpolar range (Trathan et al 1996;Wilson et al 2001;Fraser and Hofmann 2003;Jenouvrier et al 2006;Hinke et al 2007). The weight of evidence suggests that Adélie penguins are sensitive to environmental variability.…”