Browsing by Author "Von der Heyden, Sophie"

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    Genetics and ecosystem effects of the invasive mussel Semimytilus algosus, on the West Coast of South Africa
    (2016) Zeeman, Susanna Catharina Franzina; Branch, George M; Pillay, Deena; Von der Heyden, Sophie
    Invasive species can radically affect community composition and ecosystem processes, and human traffic has accelerated their spread. On the South African coast, 86 invasive species have been recorded, although until recently only the Mediterranean mussel Mytilus galloprovincialis and the barnacle Balanus glandula have had significant ecosystem effects on a large geographic scale. Semimytilus algosus was first detected at Elands Bay in 2009 and by 2010 it occupied 500 km of the West Coast of South Africa from Groenriviermond to Bloubergstrand. Given the fact that it is an ecosystem engineer forming dense beds, it is likely to have marked community effects. My study aimed to determine: (A) the identity, genetic composition and origin of the population, and (B) potential interactions between M. galloprovincialis and S. algosus and their effects on community composition. I conducted surveys to assess the abundance and zonation of S. algosus, analysed its competitive abilities by comparing its life-history strategies to other mussel species on the West Coast, and conducted field experiments to examine survival and interactions between S. algosus and M. galloprovincialis at different shore heights. I confirmed the identity of this species and found that the South African population has comparable genetic variation to the Chilean and Namibian populations. It spread to South Africa, seemingly through larval dispersal from Namibia, and now ranges from Groenriviermond in the north to Hout Bay in the south, spreading southward. It is most abundant on the low shore, with M. galloprovincialis on the mid shore. Mixed beds co-exist in the transition zone. Biodiversity in S. algosus beds is similar to that in M. galloprovincialis beds. High recruitment rates of S. algosus on the low shore, and its high genetic variation at all sites, enable it to colonise rock quickly and become established in new areas. The competitive ability of Semimytilus algosus is strongly related to shore height. It cannot survive on the high shore due to intolerance to desiccation. On the low shore its high recruitment rate offsets its high mortality due to wave action and predation.
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    Parvulastra exigua in South Africa: one species or more?
    (2013) Payne, Robyn P; Griffiths, Charles L; Von der Heyden, Sophie
    Parvulastra exigua is a widely distributed and prominent member of the temperate intertidal fauna in the southern hemisphere, occurring along the southern coastline of Africa, southeastern Australia and several oceanic islands. In South Africa, it is found in sympatry with the endemic Parvulastra dyscrita and the two are differentiated predominantly by gonopore placement. P. exigua gives rise to distinct lecithotrophic benthic larvae that hatch from sticky egg masses laid via oral gonopores. In contrast, P. dyscrita has aboral gonopores that release eggs into the water column, from which pelagic larvae hatch. Several recent studies have suggested that there is a cryptic species of P. exigua in South Africa, based on genetic evidence or the differential placement of the gonopores. A morphological, anatomical and genetic investigation was performed on a total collection of 346 P. exigua and 8 P. dyscrita specimens from the east and west coast of South Africa, with the hope of confirming whether cryptic species and/or P. exigua specimens with aboral gonopores are present in the population and determining if they correlate. Neither the cryptic species, nor P. exigua specimens with aboral gonopores were obtained. This study tentatively refutes the claim of the existence of aboral gonopores in the South African P. exigua population, and the distinction between P. exigua and P. dyscrita is confirmed, with features separating these two species clarified.
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    Significant Population Structure and Little Connectivity in South African Rocky Shore Species: Implications for the Conservation of Regional Marine Biodiversity
    (2012) Wright, Daniel B; Bishop, Jacqueline M; Von der Heyden, Sophie
    South Africa has 3650 km of coastline that spans the boundary between the Atlantic and Indo-Pacific biomes. The coastal waters boast a remarkable array of biological diversity and high levels of species abundance and endemism. Currently around 23% of the coastline is formally protected via marine protected areas (MPA) with 9% enforced as no-take zones. Even with this relatively high level of protection (as compared to other nations globally) the MPA network is still relatively sparse with protected areas that are on average ~110 km apart and unevenly distributed with the majority of MPAs situated along the species-rich east coast. This has led to concerns that the current MPA network is not protecting a representative sample of the genetic diversity among marine species nor is it sufficiently genetically connected via dispersal and gene flow to ensure their long-term persistence. To test a number of questions regarding the distribution of genetic diversity and degree of population genetic structuring along the South African coast we analyzed mitochondrial DNA sequence data for 10 sessile rocky-shore species and one reef-fish that represent three distinct life history strategies. We find that the distribution of genetic diversity across the South African coastline closely mirrors the distribution of species richness, increasing from west to east. We also find similar levels of population genetic structure among brooders, broadcast spawners and live-bearers, demonstrating that life histories are a poor predictor of genetic connectivity for South African marine species. Finally, we find that estimates of effective dispersal distance for taxa from each of the life history categories are low (~0.5-1.5 km per generation) suggesting that populations within MPAs are reliant on populations in unprotected areas via a steppingstone model of genetic connectivity. In light of these findings, we discuss a number of recommendations to enhance the role of the existing South African MPA network and echo previous calls for the establishment of protected areas along the west coast.