Interspecific differences in feeding selectivity shape isotopic niche structure of three ophiuroids in the Arctic Ocean

Abstract

Understanding the mechanisms that support feeding interactions and species co-occurrence in regions subject to rapid environmental changes is becoming increasingly important to predict future trends in population dynamics. However, there is still little information available on the trophic ecology for many benthic species to help us better understand trophic interactions and individual trophic roles. Here, we used stable isotopes (δ13C, δ15N) in conjunction with the Bayesian ellipses approach to explore spatial trends in isotopic niche width and overlap of 3 syntopic arctic brittle stars (Echinodermata: Ophiuroidea; Ophiacantha bidentata, Ophiocten sericeum, and Ophiopleura borealis) in Baffin Bay (BB), the Canadian Arctic Archipelago (CAA), and the North Water Polynya (NOW). These 3 coexisting ophiuroids displayed great interspecific plasticity in foraging behaviors and showed a high degree of inter-individual dietary flexibility. However, differences in surface carbon composition drove the variability of resource utilization at the individual level across stations, which in turn affected trophic interactions, niche overlaps, and isotopic niche breadth of ophiuroids. Greater niche overlap was found in the highly productive region of the NOW, where consumers exhibited similar food selectivity, whereas an increase in niche segregation occurred in regions with greater sea-ice concentration. These results suggest that isotopic niche size reflects individual responses to fluctuations in food availability and possibly past competition, both induced by local oceanographic features. Our study indicates that niche parameters of ophiuroids can respond quickly to ecological and environmental gradients, which suggests an important adaptability of these species facing multiple stressors.