In situ growth of juvenile cockles, Cerastoderma edule, experimentally infected with larval trematodes (Himasthla interrupta)

To examine the influence of larval trematodes (metacercariae) on survivorship and growth of bivalves, juvenile cockles were experimentally infected with Himasthla interrupta and afterwards deployed in enclosures on an intertidal flat at two different tidal levels for one month. The hypothesis is that the impact of such metacercariae varies with food availability and environmental conditions. The experimental cockles exhibited significantly different growth rates at the two study sites, but there was no discernible impact of the metacercariae on survivorship and shell-growth. Body condition, however, differed among infected and non-infected cockles at the site with the shortest immersion time. Both the experimentally infected and non-infected cockles lost body condition during their incubation in the laboratory because of starvation. Infected cockles, however, lost more flesh weight than the non-infected, and this difference was maintained for high-shore cockles during the in situ experiment, whereas both infected and non-infected low-shore cockles (living under more optimal food conditions) had regained their pre-experimental body condition. In conclusion, it seems that Himasthla interrupta metacercariae are non-exploitative and relatively harmless under moderate infection intensities and normal environmental conditions.