A temporal shift in trophic diversity among a predator assemblage in a warming Arctic.

David J Yurkowski,Nigel E Hussey,Steven H Ferguson,Aaron T Fisk

doi:10.1098/rsos.180259

David J Yurkowski, Nigel E Hussey + Show 2 more

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https://doi.org/10.1098/rsos.180259

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Abstract

Climate change is leading to northward shifts in species distributions that is altering interspecific interactions at low- and mid-trophic levels. However, little attention has been focused on the effects of redistributions of species on the trophic ecology of a high trophic-level predator assemblage. Here, during a 22-year period (1990–2012) of increasing sea temperature (1.0°C) and decreasing sea ice extent (12%) in Cumberland Sound, Nunavut, Canada, we examined the trophic structure of a near-apex predator assemblage before (1990–2002) and after (2005–2012) an increase in the availability of capelin—generally an indicator species in colder marine environments for a warming climate. Stable isotopes (δ13C and δ15N) were used in a Bayesian framework to assess shifts in diet, niche size and community-wide metrics for beluga whales (Delphinapterus leucas), ringed seals (Pusa hispida), Greenland halibut (Reinhardtius hippoglossoides) and anadromous Arctic char (Salvelinus alpinus). After 2005, consumption of forage fish increased for all predator species, suggesting diet flexibility with changing abiotic and biotic conditions. An associated temporal shift from a trophically diverse to a trophically redundant predator assemblage occurred where predators now play similar trophic roles by consuming prey primarily from the pelagic energy pathway. Overall, these long-term ecological changes signify that trophic shifts of a high trophic-level predator assemblage associated with climate change have occurred in the Arctic food web.

Highlights

Climate change is leading to northward shifts in species distributions that is altering interspecific interactions at lowand mid-trophic levels
We provide the first empirical evidence of long-term (1990 – 2012) alteration to the trophic structure of a near-apex predator assemblage associated with changes in the composition of forage fish species availability coincident with a rapidly warming climate
Ringed seal diet consisted of both squid and forage fish, but similar to beluga whales, a probability of increased consumption of forage fish was greater than 99% from 1990–2002 to 2005–2012

Summary

Introduction

Climate change is leading to northward shifts in species distributions that is altering interspecific interactions at lowand mid-trophic levels. Changes to Arctic sea temperature and sea ice phenology have facilitated a punctuated poleward shift in the distribution of more temperate species including apex predators (e.g. killer whales Orcinus orca [7]), near-apex predators (e.g. harp seals Pagophilus groenlandicus [8]), forage fish (e.g. capelin Mallotus villosus [9]) and invertebrates (e.g. blue mussels Mytilus edulis [10]). This has led to observed and ongoing changes to Arctic ecosystem productivity, species abundances, population mixing and disease/ pathogen transmission for its fauna [11,12]. We examine the diet and isotopic niche of beluga whales (Delphinapterus leucas), ringed seals, Greenland halibut (Reinhardtius hippoglossoides) and anadromous Arctic char (Salvelinus alpinus) across a temporal scale that captures a rapid warming period and where capelin have become increasingly abundant since the mid-2000s [19] (A Fisk 2006, personal observation and R Kilabuk from Pangnirtung, Nunavut, 2011, personal communication)

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