Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover.

Sebastian Prati,Eirik H Henriksen,Rune Knudsen,Per-Arne Amundsen

doi:10.1002/ece3.6173

Abstract

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts.

Highlights

Seasonal studies are important to understand the ecological dynamics of host-parasite relationships
We address seasonal patterns in the intestinal parasite community of sympatric Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in subarctic Lake Takvatn, northern Norway, which is ice covered for approximately half the year
Our study revealed distinct seasonal patterns in the prevalence of several intestinal parasite taxa leading to temporal shifts in the parasite community composition in both Arctic charr and brown trout

Summary

| INTRODUCTION

Seasonal studies are important to understand the ecological dynamics of host-parasite relationships. The winter period has, traditionally been viewed as an insignificant season of low ecological importance in ice-bound lakes (Salonen, Leppäranta, Viljanen, & Gulati, 2009), and the majority of host-parasite studies in northern lake systems have addressed the ice-free period (Knudsen, Klemetsen, & Staldvik, 1996; Tedla & Fernando, 1969) This bias toward summer and autumn studies may underestimate the importance of the winter as a transmission window for parasites in high-latitude lakes. Under ice cover, both Arctic charr and brown trout feed mainly on benthic macroinvertebrates including amphipods and insect larvae in addition to increased piscivory in brown trout (Amundsen & Knudsen, 2009; Klemetsen, Amundsen, et al, 2003) Such seasonal changes in feeding ecology may be crucial for the structuring of parasite communities in salmonid hosts. The accumulation of parasites during the winter period will be important for the overall differences in parasite community seen between the two fish host species

| MATERIALS AND METHODS

Findings

| DISCUSSION