Abstract
The introduction of a large predatory snow crab, Chionoecetes opilio, into the Kara Sea is a unique situation where the impact of an invasive species affecting an otherwise undisturbed ecosystem can be observed unhindered by other ecosystem stressors. Trophic interactions are one of the principal relationships between animals and can help assess an ecosystem's stability. The trophic positions and sources of organic material for the most common benthic species of Blagopoluchiya Bay sampled at different stages of the invasion were calculated using stable isotope analysis. The most pronounced changes in the trophic web occurred amongst the megabenthic species, where previously most abundant deposit-feeding ophiuroids have disappeared. However, the benthic species' trophic position and primary production source preference did not change. A sea star, Urasterias lincki, remained the highest carnivore in the bay, and the invasive crab remained at a lower trophic level, showing higher omnivory in its diet. Any changes in the consumers' prey items were within the same trophic level. Overall, active predators became one of the most abundant feeding mode groups. The average weighted trophic position of all megabenthic species increased to the third trophic level, where mostly secondary consumers remained.