MEPS 286:13-19 (2005)  -  doi:10.3354/meps286013

ABSTRACT: Worldwide introductions of species have raised concern about ecological and economic impacts. However, research on actual impacts of introduced species on native biota is rare. The American slipper limpet Crepidula fornicata (L.) was unintentionally introduced to Europe in the 1870s with oysters imported for farming purposes. Since C. fornicata is a filter-feeder, trophic competition and associated negative effects when epizootic on bivalves have been assumed. This study is the first to experimentally test in the field effects of the epizootic C. fornicata on survival and growth of its major basibiont in northern Europe, the blue mussel Mytilus edulis L. In 2 field experiments of 12 wk each, epigrowth by C. fornicata resulted in a 4- to 8-fold reduction in survival of mussels, equivalent to a mortality of 28 and 30%, respectively. Shell growth in surviving mussels with attached C. fornicata was 3 to 5 times lower compared to unfouled mussels, but similar to that with artificial limpets. As a causative agent, interference competition in the form of changes in small-scale hydrodynamics due to C. fornicata stacks is suggested. This may result in a high energy expenditure for byssus production of mussels. Trophic exploitation competition does not seem to be relevant. In general, interference and not exploitation competition is suggested to be the major impact of epizootic C. fornicata on its basibionts in Europe. However, the generality of this assumption has to be verified by investigating different C. fornicata-basibiont associations. This stresses the need for a species-by-species approach under diverse environmental settings in assessing impacts of introduced species. In the case of M. edulis, this study shows that C. fornicata has the potential to act as an important mortality factor.

KEY WORDS: Crepidula fornicata · Mytilus edulis · Impact · Introduced species · Epibiosis · Interference competition · Mortality · Growth