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

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 (<i>Delphinapterus leucas</i>), ringed seals (<i>Pusa hispida</i>), Greenland halibut (<i>Reinhardtius hippoglossoides</i>) and anadromous Arctic char (<i>Salvelinus alpinus</i>). 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.