A small increase in temperature could rapidly expand the latitudinal range and pathogenicity of the marine trematode parasite Curtuteria arguinae

The phenology and transmission dynamics of the marine trematode Curtuteria arguinae were investigated, a parasite whose recently elucidated life cycle involves oystercatchers (Haematopus ostralegus), needle snails (Bittium reticulatum), and edible cockles (Cerastoderma edule). To assess the influence of temperature and light on cercarial emergence, infected B. reticulatum were exposed to temperatures ranging from 15 °C to 27 °C under both light and dark conditions. Cercarial emergence peaked under warm and illuminated conditions, showing strong temperature dependence, and, to a lesser extent, light dependence. Emergence occurred significantly at temperatures ≥21 °C, with median emergence rates of 12–47 cercariae.day⁻¹, and the positive influence of light was overruled at higher temperatures. A 22-year dataset from Arcachon Bay (France) was also analyzed to determine the timing of first infections in cockles relative to sea and air temperatures, as well as cockle shell size, across ten cohorts. First infections of cockles were consistently observed in late summer, with a mean sea temperature of 20.8 °C, placing cercarial transmission once a thermal threshold is reached. This thermal dependency explains the parasite's current southern distribution. With climate warming, its range is likely to expand northward along the northeastern Atlantic coast, in areas where all hosts are already present. Expansion may also be supported by the northward extension of B. reticulatum. In areas where the parasite is already established, rising temperatures may enhance cercarial output and infection intensity, increasing pathogenic effects on both intermediate hosts and posing a growing threat to ecosystem functioning and cockle fisheries.