Invaders interfere with native parasite–host interactions
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The introduction of species is of increasing concern as invaders often reduce the abundance of native species due to a variety of interactions like habitat engineering, predation and competition. A more subtle and not recognized effect of invaders on their recipient biota is their potential interference with native parasite–host interactions. Here, we experimentally demonstrate that two invasive molluscan filter-feeders of European coastal waters interfere with the transmission of free-living infective trematode larval stages and hereby mitigate the parasite burden of native mussels (Mytilus edulis). In laboratory mesocosm experiments, the presence of Pacific oysters (Crassostrea gigas) and American slipper limpets (Crepidula fornicata) reduced the parasite load in mussels by 65–77% and 89% in single and mixed species treatments, respectively. Both introduced species acted as decoys for the trematodes thus reducing the risk of hosts to become infected. This dilution effect was density-dependent with higher reductions at higher invader densities. Similar effects in a field experiment with artificial oyster beds suggest the observed dilution effect to be relevant in the field. As parasite infections have detrimental effects on the mussel hosts, the presence of the two invaders may elicit a beneficial effect on mussels. Our experiments indicate that introduced species alter native parasite–hosts systems thus extending the potential impacts of invaders beyond the usually perceived mechanisms.
KeywordsIntroduced species Dilution effect Parasitism Transmission Trematodes Cercariae
We wish to thank Maria Donas-Bôtto Bordalo and Alejandro Caballero Hernández for help with the experiments. For help with the ring experiment at Sylt we thank Christian Buschbaum, Patrick Polte and Nils Volkenborn. This work was supported by a fellowship to DWT within the Postdoc-Programme of the German Academic Exchange Service (DAAD).
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