| Summary: | Thesis (MSc) -- Stellenbosch University, 2015. ENGLISH ABSTRACT: Polydorid polychaetes infest commercially important shellfish such as the oyster, Crassostrea gigas, and can cause financial losses to the industry. Early shipping voyages from Europe to South Africa, and the importation of oyster spat from USA, France, UK, Chile and Namibia, has most likely led to the introduction of non-native shell-boring polydorids in South Africa. Additionally, oysters are often moved between farms which may spread these pests further. The most prevalent southern African polydorids infesting farmed C. gigas are the indigenous Boccardia pseudonatrix, the introduced Polydora hoplura and a species tentatively identified as Polydora ciliata/calcarea. The aims of this study were therefore to 1) confirm the identity of P. ciliata/calcarea and to 2) determine the genetic structure of the three pests and compare these structures to a control for natural dispersal (Boccardia polybranchia) to determine if pests worms are a) being moved with oysters, b) moving between farm and wild sites or c) moving naturally between sites, facilitated by ocean currents along the southern African coast. Traditional taxonomic characters were used to identify species, and revealed that P. ciliata/calcarea morphologically closely resembles Polydora websteri from Japan and Australia. To confirm this identity, an 18S rRNA phylogeny of 1759 bp was constructed for P. ciliata/calcarea, P. websteri from Japan, Australia and USA and other morphologically similar species. The phylogeny supported the morphological data; southern African specimens differed by only 2 bp (0.1%) from Japanese and Australian P. websteri specimens. However, they all differed markedly (29 bp/1.6%) from P. websteri from near the type locality in the USA. It was therefore concluded that American specimens represent the “true” P. websteri, and that southern African, Japanese and Australian specimens represent a morphologically similar, but genetically distinct species, here referred to as ...
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