Understanding drivers of parasite community structure is compromised by poor sampling and historical focus on one host-one parasite systems. Yet parasites are ubiquitous and co-infections are common. This study aimed to identify how various drivers, ranging from landscape scale (waterbird movements, hydrological connectivity, region, host distribution) to within-host level (host–parasite interactions and parasite–parasite interactions), contribute to structuring endoparasite metacommunities of malacosporean myxozoans infecting dormant propagules (statoblasts) of the freshwater bryozoan, Cristaella mucedo.

Myxozoan infections present in statoblasts collected from hydrologically connected and isolated sites in different regions across the UK were identified by PCR to estimate infection prevalence and an RFLP assay to characterise diversity. Data from The Wetland Bird Survey and BirdTrack were used to quantify waterbird connectivity based on species turnover at each site. Host genotypes were described by microsatellites. 

Overall myxozoan infection prevalence was associated with high waterbird turnover at the site level. Hydrological connectivity was linked with reduced parasite diversity but not prevalence, with hydrologically isolated sites supporting higher richness. Regional variation in malacosporean diversity and abundance was evident, with a markedly different community supported in Northern Ireland. Co-infections within statoblasts were common. Uninfected statoblasts were larger and statoblasts with single vs. multiple infections were similar in size. Co-occurrence analysis identified positive associations between four RFLP infection profiles. There was no evidence that host–parasite interactions result in local adaptation of parasites to host clones.

Our study provides evidence that ongoing waterbird movements promote parasite persistence and proliferation and that isolated sites are hotspots for malacosporeans in C. mucedo populations. Co-occurrence patterns imply that malacosporeans infecting statoblasts do not compete and that some may facilitate the presence of others. Our collective evidence suggests that metacommunity dynamics (widespread dispersal and colonisation) structure bryozoan host and affiliated malacosporean populations across the landscape and preclude persistent host–parasite interactions that would lead to local adaptation.