Trophic niches of benthic crustaceans in the Pechora Sea suggest that the invasive snow crab Chionoecetes opilio could be an important competitor

Abstract Expanding human activities alongside climate change, the introduction of invasive species and water contamination pose multiple threats to the unique marine ecosystems of the Pechora Sea in the Russian Arctic. Baseline data on biodiversity and responses to environmental change are urgently needed. Benthic decapod crustaceans are globally distributed and play an important role in fisheries, yet their roles in food webs are less understood. In this study, we used an integrated approach combining stomach content analysis and stable isotope analyses (δ 13 C and δ 15 N) to examine the trophic niches of three decapod species in the Pechora Sea including the invasive snow crab Chionoecetes opilio and two species of native decapods, the spider crab Hyas araneus and the hermit crab Pagurus pubescens . Stomach contents of 75 decapods were analysed ( C. opilio n = 23; H. araneus n = 9; P. pubescens n = 43), and 20 categories of prey items were identified with the most frequently occurring prey items being bivalve molluscs ( Ciliatocardium ciliatum , Ennucula tenuis , Macoma calcarea ) , polychaetes, crustaceans and plant debris. Bayesian ellipse analyses of stable isotope signatures ( n = 40) revealed that C. opilio displays an overlapping trophic niche with the two native decapods, providing direct evidence that the invader likely competes for food resources with both H. araneus and P. pubescens . As such, the presence of this invasive species could hold important consequences for trophic interactions, benthic ecosystem functioning and biodiversity. Microplastics were also found to be a likely stressor on this ecosystem, as 28% of all stomachs contained digested microplastics among other items. Long-term studies of benthic ecosystem structure and functioning are now needed to more fully understand the extent to which this new competitor may alter the future biodiversity of the Pechora Sea alongside the additional stressor of digested plastics.