Ectoparasite infestation and host–parasite trophic relationship for Champsocephalus gunnari (Lonnberg, 1905) at South Orkney Islands, Antarctica

An analysis of ectoparasite infestations in Champsocephalus gunnari at South Orkney Islands, Antarctica, was performed, which revealed the prevalence, mean abundance, and mean intensity of the two species of parasites collected. The parasites’ preference for parts of the infested host fish was also investigated. The host–parasite trophic relationship was further examined using stable carbon and nitrogen isotopic analysis. The results showed that Eubrachiella antarctica was more inclined to parasitize the fins of C. gunnari. The carbon isotope ratio (δ¹³C) of the host was negatively correlated with the values for carbon isotopic discrimination (Δδ¹³C) between host and E. antarctica. The relationship between E. antarctica and C. gunnari is considered “parasitic” because E. antarctica has a higher trophic level than that of host C. gunnari, while Trulliobdella capitis may be a carrier parasite of C. gunnari or show a “symbiotic” relationship with it. The ecological niche spaces of the three species do not overlap, indicating the existence of specific trophic niches in the marine food web. This study highlights the importance of including parasites into the study on food web structure and trophic dynamics.