MEPS 565:113-129 (2017)  -  DOI: https://doi.org/10.3354/meps12023

ABSTRACT: Understanding the trophic ecology of an invasive species is important for risk assessment. The red king crab Paralithodes camtschaticus is both a valuable fishery resource and a potential threat to native biota in the Barents Sea. We combined gut content analysis and stable carbon and nitrogen isotope analysis to study feeding strategy, variation in resource use and niche overlap within the benthic food web of Porsangerfjord (70.1° to 70.9°N, 25° to 26.5°E) on the northern Norwegian coast. This fjord has experienced recent invasion by the red king crab. Sediment-dwelling bivalves and polychaetes dominated gut contents of the red king crab with respect to occurrence, and the wide range of prey from multiple trophic levels revealed a generalist, opportunistic feeding strategy. There were differences in diet related to crab size and foraging location, reflecting habitat choice and depth distribution of crabs during their life cycle. Small crabs, feeding in shallow water, relied to a larger extent on littoral species such as sea urchins and gastropods. The estimated mean trophic level for red king crab in Porsangerfjord was 3.1 (range 2.7-3.5). There was no evidence of a pronounced ontogenetic niche shift in stable isotopes, with local effects concealing possible overall size effects. Competition may arise with native anomuran species (e.g. Lithodes maja), large predatory asteroids and gastropods, all of which overlapped with red king crab in isotopic niche. A low overlap in isotopic niche between red king crab and fish suggests that they exploit different major food resources and that predatory fish occupy a higher trophic position than the red king crab in Porsangerfjord.

KEY WORDS: Decapod · Diet · Stable isotopes · Trophic ecology · Trophic level · Introduced species · North Atlantic