Project
DNA identification of shellfish species and hybrids
In the annual WOT Shellfish stock assessments the common cockle (Cerastoderma edule) and Manila clam (Ruditapes philippinarum) are target species because of their importance for fisheries and as food for birds. Both species highly resemble other shellfish species, respectively the lagoon cockle (Cerastoderma glaucum, in lakes Grevelingenmeer and Veerse Meer) and grooved carpet shell (Ruditapes decussatus). Both cockle species can in theory be distinguished based on clearly documented characteristics, but they often appear to exhibit hybrid features making them very difficult to identify. They are known to be able to interbreed but it is unknown whether they actually hybridize in Dutch waters. For both carpet shells there are clearly defined characteristics for shell features and siphon features, but again there appear to be hybrid forms. Identification of carpet shells is even more difficult because often only their siphons are collected, without any shell fragments. Siphon may even resemble those of the pullet carpet shell (Venerupis corrugata) and false angelwing (Petricolaria pholadiformis). Such identification uncertainties, or even the existence of hybrid forms, may lead to significant errors in stock assessments.
In the annual shellfish surveys in Dutch coastal waters certain species are difficult to distinguish from each other based on visual identification characteristics alone. These are the common and lagoon cockle (C. edule & C. glaucum) and the Manila clam (R. philippinarum) and indigenous carpet shells (R. decussatus & V. corrugata). The latter often have to be identified based on their siphons alone. Both sets of species appear to show intermediate identification characteristics and may interbreed leading to hybrid forms. In order to reduce a potential error in stock assessments of the commercially important C. edule and R. philippinarum we propose to study whether these species hybridize in Dutch coastal waters and to improve identification keys, also for siphons only. We will use a combination of traditional identification methods and DNA analyses.