Ecosystem Links: Macrophytes, Snail Preferences, and Trematode Transmission in Man-Made Water Bodies

Freshwater snails act as obligate intermediate hosts for trematode parasites that cause trematodiases threatening public and veterinary health, and biodiversity conservation. Therefore, interest has re-emerged in snails as a target for disease control, yet their ecology is poorly understood. We studied the relationship between physical and chemical water parameters, macroinvertebrates, macrophytes, land use, and snail abundance, diversity, and infection rate in man-made reservoirs in eastern Zimbabwe. We observed no significant relationship between water quality parameters or macroinvertebrates and snail communities, but a significant association existed between specific macrophytes and snail species. Schistosome-competent snails (i.e., Biomphalaria pfeifferi and bulinids) were most associated with emergent Cladium mariscus, whereas Physella acuta was associated with submerged oxygen weed, Lagarosiphon major. This offers a possibility to incorporate the management of macrophytes in integrated snail control schemes. Diversity of freshwater snail species significantly varied across land use types with the lowest observed diversity in the commercial tobacco farm section, dominated by invasive exotic P. acuta and Pseudosuccinea columella, as compared to the less impacted conserved area, reflecting the adverse effects of agriculture on biodiversity. Out of the 547 schistosome host snails, 88 were shedding cercariae (16.1%) of various types, including schistosomes and amphistomes. We did not find any significant associations between macroinvertebrate or macrophyte diversity and snails and their infection rate.