Effects of temperature, salinity, and pH on the survival and activity of marine cercariae.

Alterations of abiotic factors due to global climate change are predicted to impact disease dynamics, particularly for pathogens with complex life cycles involving free-living infectious stages, such as the cercariae of trematode parasites. Previous investigations of cercarial output, longevity, and infectivity suggest an overall increase in trematode transmission in response to elevated temperature. However, while increased temperature will likely be accompanied by changes in salinity and pH in marine ecosystems, little is known regarding their influence on cercariae. We investigated the response of trematode cercariae of the intertidal horn snail Cerithidea californica to altered temperature, salinity, and pH. The survival and activity of one trematode species, Euhaplorchis californiensis (Heterophydae), appears to be largely unaffected by increased temperature, while that of a second species, Acanthoparyphium spinulosum (Echinostomatidae), decreased at the warmer temperature (25 degrees C). Cercariae of E. californiensis generally fared best at the highest salinity (40 ppt), whereas A. spinulosum showed the opposite effect. Neither species was affected by pH alone although there were interactions with salinity and time. These results may reflect different emergence patterns of the two species and demonstrate that trematode parasitism in intertidal zones may be impacted by alterations of the marine environment resulting from climate change.