Benefit from an invader: American slipper limpet <Emphasis Type="Italic">Crepidula fornicata</Emphasis>reduces star fish predation on basibiont European mussels

Introduced species have recently become a major concern in ecological research and aquatic conservation. This is due to an increasing appearance of introduced species at a global scale and a multitude of negative impacts on native biota. However, impacts of introduced species are not necessarily only negative. The epizootic American slipper limpet Crepidula fornicata, native at North American Atlantic shores, was introduced to Europe in the 1870s and is now widespread along the Atlantic coast of Europe. Negative effects like trophic and spatial competition have been reported. In its major basibiont in the Wadden Sea, the blue mussel Mytilus edulis, attached limpets reduce survival and growth. However, a laboratory experiment also showed sea star (Asterias rubens) predation on mussels with limpet epigrowth to be three times lower than in unfouled mussels. Hence, although negatively affected by C. fornicatain one way, this epigrowth is beneficial for fouled mussels in another. This indicates that the actual impact of an introduced species is a complex interplay of positive and negative effects which may only be revealed experimentally.