MEPS 319:129-134 (2006)  -  doi:10.3354/meps319129

ABSTRACT: Trematode parasites can affect the molluscan hosts serving as first intermediate hosts in their complex life-cycles in manifold ways, but little is known about trematode-induced effects in second intermediate mollusc hosts. In 2 field experiments in 2 habitats and at 2 tidal heights (low and mid intertidal), controlled infection of blue mussels Mytilus edulis serving as second intermediate hosts for larval stages (metacercariae) of the trematode Renicola roscovita resulted in significant lower growth of parasitized compared to non-parasitized individuals. However, tidal height had a stronger effect on mussel growth than parasitism, without any interaction between the 2 factors. The negative effect of R. roscovita metacercarial infections on mussel growth is thought to result from direct tissue disruptions, interference of metacercariae (located in palps and visceral mass) with food intake ability, and growth of metacercarial cysts within the host. Mussel growth was negatively correlated with the number of metacercariae, but this relation was significant only at the mid and not at the low intertidal sites. This may indicate that parasites act as background stressors that affect their hosts depending on additional environmental stress such as (e.g.) food shortage, desiccation and heat, which all increase with the increasing aerial exposure. The results of this study show that trematode infections can be an important determinant of bivalve growth, with potential economic implications for mussel cultivation.

KEY WORDS: Trematodes · Bivalves · Growth · Parasites · Field experiment · Controlled infections