Authors

Discussion

The success and ecological impact of parasite invasions may be modulated by another anthropogenic stressor, climate change. Temperate coastal ecosystems are disproportionately affected by both and therefore at an elevated risk for the combined effects. Here, we study parasite dynamics in a temperate coastal ecosystem, using temperature experiments and two parasite species that share the blue mussel (Mytilus edulis) as their host. In controlled laboratory experiments in a range of temperatures (10°C-26°C), we investigated warming effects on the lifecycles of two species of invasive parasitic copepods (Mytilicola intestinalis, Mytilicola orientalis), and on the survival, growth, condition, and reproductive status of infected and uninfected native mussel hosts. The two species of parasites are closely related, but have different invasion histories in Northwestern Europe, including the Dutch Wadden Sea; M. intestinalis invaded the system 90 years ago while M. orientalis arrived only 20 years ago, originally inhabiting warmer climate regions. Our experiments showed that in both parasites, an increase in temperature accelerated the development speed of both free-living and parasitic life stages, with the effect being most pronounced in the lower temperature range (10°C-14°C). Only the highest temperature (26°C) limited the egg development success of M. intestinalis and host entry success of both parasite species. Mussel survival decreased at 26°C but infection with either parasite species did not affect it. Infection with M. orientalis decreased mussel shell growth and infection with M. intestinalis lowered mussel condition indices, with these infection effects remaining uniform across temperatures. Mussel reproductive status was highest at the lowest temperatures (10°C-14°C) and infection with either parasite did not affect reproduction. These findings indicate that an increase in temperature enables a higher number of parasite life cycles to be completed per year, which can result in a higher infection pressure on hosts. Because infections affect host growth and condition, the increase in infection pressure is expected to lead to fewer resources for physiological functions such like growth, reproduction, and immune responses. Heatwave temperatures are likely to be harmful for both the host and M. intestinalis, while the more recent invader M. orientalis will be less impacted. These results foster our understanding of climate change impacts on invasive parasites and can inform ecosystem models that evaluate the impact of nonlethal parasites.