Complications of a non-native oyster introduction: facilitation of a local parasite

Among the risks of introducing non-native species to novel environments is the possibility that the non-native might serve as a reservoir for enzootic pathogens formerly at low abundance. The recent identification of Bonamia sp. in previously uninfected non-native Suminoe oysters deployed to Bogue Sound, Morehead City, North Carolina, USA, raises serious concerns about the oyster's ability to act as a reservoir for the parasite, not formerly known along the east coast of the USA. To assess the current distribution of the Bonamia sp. parasite and its environmental tolerances, non-reproductive triploid Suminoe oysters, certified as uninfected, were deployed at 5 high salinity sites across North Carolina, chosen because of their similarity to the Bogue Sound site, and along a salinity gradient radiating from Morehead City Port, at which the parasite is known to occur. Screening of 2 oyster cohorts failed to detect the Bonamia sp. parasite beyond the immediate vicinity of Morehead City port. At the port, infection was almost entirely confined to small (<40 mm shell height) oysters. These results suggest that the parasite, which is genetically similar to Australasian species, is a recent ballast water introduction through Morehead City Port and that its spread may be dependent on the availability of suitable hosts in high salinity environments. Clearly, the proposed introduction of the Suminoe oyster to the mid-Atlantic coast of the USA represents considerable economic and ecological risk and should not proceed without further study to obtain better estimates of likely effects.