Browsing by Author "Jackson, Sue"

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    Mind the gap – context dependency in invasive species impacts : a case study of the ascidian Ciona robusta
    (Pensoft Publishers, 2017-01-04) Robinson, Tamara B.; Havenga, Brendan; Van der Merwe, Marlene; Jackson, Sue; Ruiz, Gregory
    ENGLISH ABSTRACT: In the face of increasing invasions and limited resources, appropriate management of invasive species requires prioritisation of species for management action. This process often relies on knowledge of species specific impacts. However, as studies explicitly measuring impact of marine alien species are rare, prioritisation of management actions is often based on studies from outside the geographic area of interest. Further, few impact studies account for context dependency (e.g. seasonal variability or distinct environmental regimes), raising the question of how transferrable knowledge about the impact of a species is between invaded ranges. This study addressed this question by using the widespread invasive solitary ascidian Ciona robusta as a case study for assessing impacts across two invaded regions: South Africa and California, USA. We replicated a previously conducted experiment from California that showed that C. robusta depresses local species richness in San Francisco Bay. Our South African experiment showed no effect of C. robusta on species richness, the Shannon-Weiner diversity index or community composition, despite experiments being carried out over two years and at two depths. While these results may reflect strong density dependency in the impact of C. robusta, they serve to highlight context dependency in invasive species impacts. This suggests that until studies of impact in marine systems become common place, context dependency should be explicitly addressed as a source of uncertainty during the prioritisation of species for management action.
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    Mussel and oyster culture in Saldanha Bay, South Africa : potential for sustainable growth, development and employment creation
    (Springer, 2013-02) Olivier, David; Heinecken, Lindy; Jackson, Sue
    Worldwide declines in fish stocks have a significant impact on the livelihoods of coastal fishing communities as jobs are lost and alternative forms of employment are limited. Mariculture (marine aquaculture) is considered by governments to be a viable solution to address unemployment and poverty in such communities. In Saldanha Bay, South Africa, the growing mussel and oyster industry has considerable potential for poverty alleviation, hence food security enhancement. In the first part of this study, we examine the potential ecological carrying capacity of the Bay to produce bivalves, and estimate the impact of this on employment creation should the sector’s growth potential be fully realised. This growth potential could take the sector to 10 to 28 times its current size, providing direct employment for 940 to 2,500 people in the Saldanha area. Secondly, we assess five factors that affect the sustainable growth, development and employment creation potential of small-scale mariculture in South Africa and other countries. These are state support, markets, funding, the natural environment and the local community. Participants in the sector perceive its expansion potential to be hampered by regulatory issues such as incomplete implementation of a cohesive and accessible financial support policy, slow processing of mandatory samples required to monitor product safety, poor facilitation of access to international markets, price undercutting by imports subsidized in their countries of origin, and injuriously high lease fees for water levied by the parastatal harbour authority, coupled with lack of medium- and long-term lease tenure. The risk of environmental degradation from competing harbour use by large, fossil fuel and ore transport industries is of potential future concern.