Cercarial survival in an intertidal trematode: a multifactorial experiment with temperature, salinity and ultraviolet radiation.

Parasite transmission takes place in the context of a multitude of simultaneously fluctuating environmental factors. As a particularly vulnerable step in the transmission, trematode cercariae are directly exposed to ambient conditions during their search for a host. Here, we investigated the survival of cercariae of the intertidal trematode Maritrema novaezealandensis in a multifactorial experiment (2 × 2 × 2 design) with temperature (20 and 30 °C), salinity (35 and 40 practical salinity units (psu)) and ultraviolet radiation (UVR; exposed and not exposed) as main factors. All factors had significant effects, with cercariae dying faster at the higher temperature, increased salinity and when exposed to UVR. Full activity ceased within ~6 h in all treatments at 30 °C, except at 35 psu under no exposure to UV; in all other treatments full activity was maintained for >6 h. Several factor interactions were identified, of which the interactive negative effect of temperature and UVR was the most important. These results imply that conditions during the main transmission window of M. novaezealandensis are highly challenging for cercariae. Our findings highlight the importance of considering multiple environmental factors in the study of parasite transmission to gain a more ecologically relevant understanding of transmission dynamics.