Assessing long-term changes in taxonomic and functional parasite diversity in Norwegian freshwater fish

Abstract

Climate change driven loss of biodiversity is occurring at an unprecedented rate, especially in vulnerable high-latitude freshwater systems. Despite the increasing recognition of parasites in ecosystems, there is a lack of long-term data on freshwater fish parasites, limiting our ability to understand changes in biodiversity of these important ecosystem players. This study investigates how freshwater fish parasite communities in the Glomma River system (Norway) have changed over the last 50 years by comparing historical records from 1971 and 1996-1997 to newly obtained data from 2024. A total of 104 fish belonging to five species (Alburnus alburnus, Esox lucius, Gymnocephalus cernua, Perca fluviatilis, Rutilus rutilus) were collected and assessed for helminth and crustacean parasites. These fish harboured species-rich communities comprising 27 taxa that were identified to species or genus level. Analysis of presence/absence data and community composition measures revealed that overall species richness and prevalence remained relatively stable, but the composition of parasite communities has undergone restructuring driven by species replacement and richness differences. These findings highlight the need for determining the ecological factors underlying these community changes, providing an important point of reference for assessing future ecological changes.