Non-host organisms affect transmission processes in two common trematode parasites of rocky shores

The transmission of free-living trematode stages is mediated by various environmental factors, of which the presence of ambient organisms within the host space is a potential major determinant. In two laboratory mesocosm experiments, we investigated the influence of four intertidal rocky shore species on transmission success of cercariae of the digenean trematodes Echinostephilla patellae (encysting in the tissue of blue mussels Mytilus edulis) and Parorchis acanthus (encysting on mussel shells). Encystment success of both parasite species was significantly lower in the presence of test organisms when compared to controls. Observations revealed that barnacles Austrominius modestus actively filtered cercariae, whereas the larvae were obstructed by the seaweeds Corallina officinalis and Fucus serratus. Anemones Actinia equina both physically disturbed and consumed cercariae. In a further laboratory experiment, grazing gastropods (Littorina littorea, Patella vulgata, and Gibbula umbilicalis) were found to significantly reduce the numbers of P. acanthus metacercariae in artificially prepared dishes by ingestion of cysts. Our results suggest that non-host organisms may play a key role in regulating the transmission of free-living trematode stages in rocky shore ecosystems, which is especially important with regard to the relative diversity and density of species in these habitats. The findings also emphasize the need to include parasites into marine food webs, since cercariae seem to be consumed by certain organisms to a considerable extent and could possibly represent an important energy source.     

Lagrangian dispersion modeling of vehicular emissions from a highway in complex terrain

Transit traffic through the Austrian Alps is of major concern in government policy. Pollutant burdens resulting from such traffic are discussed widely in Austrian politics and have already led to measures to restrict traffic on transit routes. In the course of an environmental assessment study, comprehensive measurements were performed. These included air quality observations using passive samplers, a differential optical absorption spectroscopy system, a mobile and a fixed air quality monitoring station, and meteorological observations. As was evident from several previous studies, dispersion modeling in such areas of complex terrain and, moreover, with frequent calm wind conditions, is difficult to handle. Further, in the case presented here, different pollutant sources had to be treated simultaneously (e.g., road networks, exhaust chimneys from road tunnels, and road tunnel portals). No appropriate system for modeling all these factors has so far appeared in the literature. A prognostic wind field model coupled with a Lagrangian dispersion model is thus presented here and is designed to treat all these factors. A comparison of the modeling system with results from passive samplers and from a fixed air quality monitoring station proved the ability of the model to provide reasonable figures for concentration distributions along the A10.