Abstract
Until recently, populations of broadcast spawning coastal invertebrates have been considered panmictic, but numerous studies have identified genetic structure at surprisingly small geographical scales. The present study investigated the role of coastal currents in shapingthe genetic structure in one of southern Africa’s best studied marine invertebrates, the brown mussel Perna perna, within Africa’s most intensively monitored marine regions, the “Sentinel Site” on the south-east coast of South Africa. Unlike previous studies, most of which used slow-evolving mitochondrial DNA markers and all of which inferred larval connectivity on the basis of genetic structure found in adults, the present study used more informative polymorphic microsatellite data that were generated for both adults and larvae collected at nearshore sites. Concurrent with previous studies carried out on the same coastline, a western and an eastern mussel lineage were identified whose ranges overlap in this region. There was however also evidence that the eastern lineage can be subdivided further into two microsatellite-based clusters. The range of one extends to the east coast, while that of the other seems to be centered on the eastern portion of the south-east coast. Adult sites could be assigned to either the western or the eastern lineage, with no intermediate populations. Larvae were relatively homogeneous throughout the study area, but most, including those in the western portion of the Sentinel Site, could be assigned to the eastern lineage, suggesting that the majority of larvae found in the nearshore western areas contribute little to larval settlement at those sites. The present study suggests that most of the larvae may have originated from the area east of the Sentinel Site. Moreover, those larvae that have been dispersed over such scales by cross shore and offshore transport do not necessarily establish themselves in the new habitats. Thus, adults are not panmictic as previously thought and larvae are “open” across a broad, 150 km range of origin. These patterns reinforce that differential delivery, where some sites receive more settlers than others, really could shape...
M.Sc. (Zoology)