Endoparasites of the Imperial Cormorant (Leucocarbo atriceps) in the Falkland Islands: investigation of secondary hosts and detection methods.

Seabirds are important apex predators and valuable sentinels of marine ecosystem health. Because they integrate signals from multiple trophic levels, their diet provides important insights into marine food-web dynamics, gastrointestinal parasite fauna, and the impacts of human activities. Changes in diet composition can affect seabird reproductive success, health status and parasite load. Many protozoan and helminth parasites depend on predator-prey interactions to complete their life cycles, making dietary analysis a useful tool for understanding parasite transmission and ecology. Here, 82 pellets were collected from an Imperial Cormorant (Leucocarbo atriceps) colony in the Falkland Islands/Malvinas Islands (51°43’S, 61°19’W) in 2020 and 2022. Preys were identified using hard remains and metazoan endoparasites using morphological and genetic identification. Parasitological analysis of pellets was performed using the standard sodium-acetate-formaldehyde method (SAF). The diet primarily consisted of fish, particularly ray-thinned fish species (Patagonotothen spp.), crustaceans [squat lobsters; (Munida spp.)], and to a lesser extent polychaetes and cephalopods. The presence of nematodes of the family Anisakidae, including the genus Contracaecum, was detected using both methods (PCR and SAF). The comparison with the diet suggests that ray-thinned fish (Patagonotothen spp.) likely act as paratenic hosts for Contracaecum (Anisakidae) infections in the Imperial Cormorant. Further, a fish-borne trematode (Heterophyidae) was detected by SAF, which is the first reported in free-ranging Imperial Cormorants. However, no relationship could be demonstrated between this parasite and prey. Further studies are necessary to fill the gaps in our knowledge of parasites’ life cycles and their effects on Imperial Cormorant’s health in the Falklands.