Influences of land use and ecological variables on trematode prevalence and intensity at the salt marsh‐upland ecotone

Abstract

AbstractHuman‐altered shorelines make up approximately 14% of the coastline in the United States, with consequences for marsh ecosystems ranging from altered physical and biological variables, to direct loss of intertidal marsh habitat, to diminished land–sea connectivity. Trophically transmitted parasites that require connectivity between upland host species and marsh host species to complete their complex lifecycles could be particularly sensitive to the effects of shoreline alterations. They can additionally respond to gradients in natural physical and biological factors, including the host communities, that are often sharp at the land–sea ecotone. Across 27 salt marshes over 45 km, we evaluated the effects of environmental variables and three types of land use (undeveloped; single‐house adjacent to the marsh with small‐scale shoreline armoring; and single‐house adjacent to the marsh without shoreline armoring), on infection prevalence and intensity of the trematode Microphallus basodactylophallus in its second intermediate crab host, Minuca pugnax. The first intermediate hosts of M. basodactylophallus are Hydrobiid snail species that are obligate marsh residents, while the definitive hosts are terrestrial rodents and raccoons. Thus, trematode transmission must depend on cross‐boundary movement by the definitive hosts. We found that although there was a trend of lower infection prevalence at undeveloped forested sites, there was no significant effect of adjacent land development on infection prevalence or intensity. Instead host, biotic and abiotic factors were correlated with infection; namely, larger M. pugnax had higher prevalence and intensity of M. basodactylophallus, and higher soil moisture and lower density of the ribbed mussel (Geukensia demissa) were associated with increased M. basodactylophallus prevalence. The small, indirect influence of upland development suggests that movement of definite hosts across the ecotone may be largely unaffected. Further, the robust trematode levels signify the ecosystem and the species interactions, upon which its complex lifecycle depends, are largely intact.