Comparison of particle processing by two introduced suspension feeders: selection in Crepidula fornicata and Crassostrea gigas

In order to understand the trophic interactions between 2 introduced suspension feeders in Europe, the North American slipper limpet Crepidula fornicata (Gastropoda) and the Pacific oyster Crassostrea gigas (Bivalvia), it is first necessary to determine the characteristics of their feeding mode. In particular, no information has been previously available concerning the capacity for qualitative particle selection - typical of C. gigas - in C. fornicata. Firstly, we investigated the anatomical-functional potential for selection in the feeding structures of C. fornicata using scanning electron microscopy, video-endoscopy, histology and mucocyte characterization. Secondly, the relative performance of qualitative selection by these 2 species was compared under experimental particle concentrations similar to those in the natural habitat, using the naturally occurring diatom Coscinodiscus perforatus var. pavillardii and the live cell/empty, cleaned frustule approach. In contrast to C. gigas, the feeding structures of C. fornicata showed no anatomical or functional potential for qualitative selection. Furthermore, although C. gigas demonstrated significant qualitative selection in selection experiments, C. fornicata demonstrated none. This fundamental difference in suspension- feeding mode will predetermine the approaches that can be used in future studies on trophic interactions, and suggests that the degree of diet overlap will depend on the extent and time periods within which oysters engage in qualitative selection.