The culture of oysters and abalone are two of the most important components of mariculture in South Africa. Both animals are, however, prone to infestation by shell-boring polychaetes, particularly members of the Polydora-group (Polychaeta: Spionidae). Infestation by these worms may pose a health risk to their hosts and an economic risk to the farmers. They may, however, also pose an environmental risk if worms are inadvertently carried beyond their natural distribution ranges through the movement, local or international, of the hosts. My research therefore focuses on aspects of polychaete taxonomy, reproduction and population structure, all of which may have implications for the infestation and spread of shell-infesting worms.
Over the last few years my research group has been identifying the worms associated primarily with abalone and a range of wild molluscs, including abalone. We found that farmed abalone are infested by a small percentage of the species that infest wild molluscs and that the most problematic worm is not indigenous and still absent from wild molluscs. More recently we have expanded our focus to include farmed oysters. Oysters and abalone are cultured differently; abalone are farmed on-shore and can spend up to four years in production while most oysters are grown off-shore for approximately one year before harvesting. These differences can have a significant impact on the composition of the species infesting the molluscs.
Of significant concern to us are the consequences of moving molluscs and their worms. Should a non-indigenous worm become established on a farm, it could escape and infest wild molluscs. They can also be spread within the destination country through the local movement of infesting hosts accelerating the spread in the natural environment. This is particularly important in South Africa where abalone and oyster farms occur in three biogeographical zones, meaning that worms can be transported across natural barriers to dispersal. Knowledge of the larval developmental modes of the worms will make an important contribution to our understanding of if and how far non-indigenous worms can spread, should they become established in the wild.
Understanding and cataloguing shell-infesting spionid polychaetes is complicated by the presence of many cryptic species – species that are morphologically similar but genetically and reproductively distinct. This may have exaggerated the current accepted global distribution of many of these species. Clarifying the taxonomic status, both morphologically and molecularly, forms the final aspect of my research.