Temperature and pCO jointly affect the emergence and survival of cercariae from a snail host: implications for future parasitic infections in the Humboldt Current system.

Ocean warming and acidification are general consequences of rising atmospheric CO concentrations. In addition to future predictions, highly productive systems such as the Humboldt Current System are characterized by important variations in both temperature and pCO level, but how these physical-chemical ocean changes might influence the transmission and survival of parasites has not been assessed. This study experimentally evaluated the effects of temperature (14, 18 and 25 °C) and the combined effects of temperature (∼15 and 20 °C) and pCO level (∼500 and 1400 microatmospheres (µatm) on the emergence and survival of two species of marine trematodes-Echinostomatidae gen. sp. and Philophthalmidae gen. sp.-both of which infect the intertidal snail Echinolittorina peruviana. Snails were collected from intertidal rocky pools in a year-round upwelling area of the northern Humboldt Current System (23°S). Two experiments assessed parasite emergence and survival by simulating emersion-immersion tidal cycles. To assess parasite survival, 2 h old cercariae (on average) were taken from a pool of infected snails incubated at 20-25 °C, and their mortality was recorded every 6 h until all the cercariae were dead. For both species, a trade-off between high emergence and low survival of cercariae was observed in the high temperature treatment. Species-specific responses to the combination of temperature and pCO levels were also observed: the emergence of Echinostomatidae cercariae was highest at 20 °C regardless of the pCO levels. By contrast, the emergence of Philophthalmidae cercariae was highest at elevated pCO (15 and 20 °C), suggesting that CO may react synergistically with temperature, increasing transmission success of this parasite in coastal ecosystems of the Humboldt Current System where water temperature and pH are expected to decrease. In conclusion, our results suggest that integrating temperature-pCO interactions in parasite studies is essential for understanding the consequence of climate change in future marine ecosystem health.