Sabellid infestations in the shells of South African molluscs: Implications for abalone mariculture

Infestations of sabellid polychaetes were found in South African-farmed abalone in 1994. Growth experiments confirmed that infested abalone had reduced growth rates. Surveys of both the intertidal and the subtidal regions at various locations around the South African coastline revealed that the sabellid was endemic to the region. It occurs in a range of mollusc species, but some species are more susceptible than others. The fact that some mollusc species become infested with worms only when exposed to them in the laboratory suggests that environmental factors may play a role in controlling natural levels of infestation. Larvae disperse by crawling and settle at the growing edge of the shell underneath the mantle. Although the larvae are benthic, there is limited transfer of larvae through the water column, which can result in export of larvae from infested tanks. The risks of dispersal are discussed in a farm management context. Abalone kept in more hygienic laboratory conditions tend to grow faster than they do in farm tanks and have lower levels of infestation by sabellid larvae. This may be because the sabellids are less fecund under these conditions, which also has implications for management.