Quarantine of oyster shell cultch reduces the abundance of Perkinsus marinus

Oyster shell is the preferred substrate for replanting oyster beds and restoring oyster reefs. If pathogens remain viable in tissues attached to shell, then planting shell may inadvertently serve as a vector for pathogen transmission. Limited local shell sources may exacerbate the problem by increasing the risk of spreading novel strains into new areas if shell is derived from other regions. In South Carolina, the primary source of oyster shell is currently the Gulf of Mexico, where the protozoan oyster pathogen Perkinsus marinus (Mackin et al. 1978) has been problematic. Although P. marinus is present in South Carolina waters, different strains exist in the two regions. Given the detrimental effects of P. marinus on oysters, protocols to minimize its spread via planting of shell are needed. We conducted a short-term, replicated experiment to follow changes in P. marinus abundance in oyster tissues by placing whole, intact oysters or shucked oysters in shell piles. The amount of oyster tissue present and parasite abundance declined precipitously after one month and was virtually eliminated by three months. Parasite persistence was dramatically longer in whole, unshucked oyster tissues as compared with those associated with shucked oysters. Viability of parasites after one month was, however, unclear. The results support the recommendation that the quarantine of shell for one month or more can dramatically reduce the potential risk of spreading P. marinus when planting oyster shell (=cultch) from other geographic areas. This recommendation is applicable to virtually any region, but several parameters such as effects of climatic conditions and shell pile configuration warrant further investigation as does the persistence of other pathogens on shell piles.