Effects of first intermediate host density, host size and salinity on trematode infections in mussels of the south-western Baltic Sea.

Claudia Bommarito,Francisco R Barboza,Fabio Pranovi,Martin Wahl,David W Thieltges,Christian Pansch

doi:10.1017/s0031182020002188

Abstract

Trematode prevalence and abundance in hosts are known to be affected by biotic drivers as well as by abiotic drivers. In this study, we used the unique salinity gradient found in the south-western Baltic Sea to: (i) investigate patterns of trematode infections in the first intermediate host, the periwinkle Littorina littorea and in the downstream host, the mussel Mytilus edulis, along a regional salinity gradient (from 13 to 22) and (ii) evaluate the effects of first intermediate host (periwinkle) density, host size and salinity on trematode infections in mussels. Two species dominated the trematode community, Renicola roscovita and Himasthla elongata. Salinity, mussel size and density of infected periwinkles were significantly correlated with R. roscovita, and salinity and density correlated with H. elongata abundance. These results suggest that salinity, first intermediate host density and host size play an important role in determining infection levels in mussels, with salinity being the main major driver. Under expected global change scenarios, the predicted freshening of the Baltic Sea might lead to reduced trematode transmission, which may be further enhanced by a potential decrease in periwinkle density and mussel size.

Highlights

Spatial heterogeneity in parasite infection levels in hosts is driven by a wide variety of environmental conditions (Anderson and Sukhdeo, 2010)
We investigated the effects of first intermediate host density and salinity on trematode infection levels in mussel second intermediate hosts in the south-western Baltic Sea
These patterns of prevalence were observed by Lauckner (1984), who, reported C. lingua prevalence to be slightly higher than that of R. roscovita and H. elongata in periwinkles collected in shallow waters

Summary

Introduction

Spatial heterogeneity in parasite infection levels in hosts is driven by a wide variety of environmental (both abiotic and biotic) conditions (Anderson and Sukhdeo, 2010). Most of the available studies focused on the density of the final host driving infection levels in downstream first intermediate hosts, whereas effects of the first intermediate host density and infection levels on second intermediate hosts have been much less studied (but see Thieltges, 2007 and Thieltges and Reise, 2007) Apart from these biotic drivers acting at the population level of a host species, infection levels can further differ at the individual host level as conspecifics may differ in their exposure or susceptibility to parasite infections, depending on habitat use, diet and other host traits (Carney and Dick, 1999). Body size has been described as a major driver of infection levels in hosts, with larger hosts offering more space and habitat for parasites, and accumulating more parasites over their lifetime than smaller and younger host individuals (de Montaudouin et al, 2000; Mouritsen et al, 2003; Thieltges and Reise, 2007; Goedknegt et al, 2019)

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Discussion

Conclusion