Browsing by Author "Bowker, Jenna"

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    Attractant properties of chemical constituents of the green macroalga Ulva and their response effects on the commercially important sea urchin Tripneustes gratilla
    (2013) Bowker, Jenna; Bolton, John J; Macey, Brett
    Interest in commercial sea urchin aquaculture is growing worldwide. This is because sea urchins have good quality roe which is a delicacy in many countries. Since the quality of sea urchin roe is dependent on what the sea urchin eats, increased research is being carried out to understand sea urchin feeding preferences. Feeding preference is related to the attractiveness/palatability of the feed, which is thought to be based on its chemical composition. Since an unpalatable feed will result in the poor quality of the organism, evaluating the palatability of sea urchin artificial feeds is important. In South Africa, the sea urchin Tripneustes gratilla has been selected for aquaculture due to its fast growth and high quality roe. Although it is a generalist herbivore, various studies have shown that T. gratilla has a significant preference for the macroalgae Ulva. The purpose of this study is to assess what chemicals contained in Ulva cause this preference. Chemosensory trials involving Ulva and its chemical constituents, as well as wounded Ulva and an artificial feed, were carried out using a Y-shaped maze. Results indicate that T. gratilla are not deterred by DMS or acrylic acid as literature suggests. Since previous studies showed that these two chemicals deter urchins, this study demonstrates that there are species-specific relationships to chemicals found in algal material. Results also indicate that T. gratilla are deterred by wounded Ulva, ulvan and ethanol, but cannot differentiate between these constituents when the constituents are compared against each other or ethanolic extract, fresh Ulva and feed. Since the sea urchins are not consistently deterred by wounded Ulva, ulvan and ethanol when compared with other constituents, this indicates that T. gratilla are not very selective in what they are attracted to or deterred from.
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    Parasites of Kunene horse mackerel Trachurus trecae (Smith-Vaniz, 1986) with a comparison of parasites of Cape horse mackerel T. capensis (Castelnau, 1861) in the northern Benguela
    (2013) Bowker, Jenna; Reed, Cecile C; Van der Lingen, Carl D
    Two species of horse mackerel (Trachurus trecae and Trachurus capensis) reside in the northern Benguela ecosystem. Both are important economic commodities for the Angolan and Namibian fisheries and therefore need to be managed appropriately. Although the two species of horse mackerel share similar morphological characteristics and co-occur in Namibian waters in the northern Benguela, few studies have compared their parasite assemblages. To date there are no studies regarding the parasite profile of T. trecae. This study is the first to identify and document the parasite assemblage of T. trecae from the northern Benguela and forms the only parasite profile for this horse mackerel species. This study also assesses the effects of fish size and fish sex on the parasite assemblage of T. trecae, and compares the parasite assemblage of this species with that of T. capensis from the northern Benguela. Results indicate that the largest significant difference in parasite assemblage is between the two horse mackerel species (by convention p<0.01), but that significant differences are also found between small and large T. trecae and between immature, male and female T. trecae. The coccidian Goussia cruciata was found to have the strongest discriminatory power in all comparisons, and therefore serves as a potential indicator parasite or biotag for discriminating between different stocks of T. trecae and between T. trecae and T. capensis in the northern Benguela. Due to the lack of literature regarding the life history of T. trecae it is difficult to assess why there are sex effects on parasites infecting this species, as well as whether the interspecific difference in parasite assemblage is due to environmental conditions or species-specific relationships. Further investigations regarding the life history of T. trecae would assist interpretation of the results obtained here. This study provides a comprehensive knowledge of the parasite assemblages infecting T. trecae and thus lends to possible future studies regarding T. trecae stock structure. It also provides a starting point for conducting studies of the parasite assemblages of other fish in the northern Benguela.
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    Using real-time forest loss alerts and global deforestation maps to assess the effectiveness of Africa's tropical protected areas
    (2015) Bowker, Jenna; Cumming, Graeme S
    Tropical rainforests harbor a significant portion of the world's remaining biodiversity. Having undergone rapid changes in forest cover over the last two decades, a large amount of irreplaceable biodiversity has been lost. The establishment of protected areas has been a key strategy to hinder the loss of tropical forests and biodiversity. However, the effectiveness of designating protected areas has been called into question, particularly in regions such as tropical Africa where widespread conditions of poverty, rapid population growth and political instability are evident. Quantitative measurements of park effectiveness for forest conservation are urgently needed, however accurate inferences concerning park effectiveness across broad regions is difficult. Whilst remote sensing techniques have been proposed as a practical solution, the intensity of data processing has made it untenable until recently. Here, I use remote-sensing methods to analyze high-resolution satellite imagery of tropical forest loss (as a proxy for tropical deforestation) within and outside 224 parks across 23 countries in Africa. I compare the extent of tropical forest loss inside parks to outside of them to show that the majority of African parks in the Subtropical and Tropical Moist Broadleaf forest biome are effective in curbing forest loss within park boundaries. However, certain parks were more effective in forest conservation than others. Whilst smaller parks were less effective at preventing forest loss inside park boundaries than larger parks, older parks were less effective than younger parks. Furthermore, parks of varying IUCN management categories exhibited negligible differences in forest loss between one another. Lastly, significant geographical variations in park effectiveness existed: West African parks exhibited the most forest loss within park boundaries and Central African parks exhibited the least. My results demonstrate the complexity of factors which influence a park's ability to curb forest loss within its boundaries. Furthermore, this study is the first bioregional-wide assessment of park effectiveness using remote sensing. These results supplement scarce literature on tropical deforestation in Africa and demonstrate the potential of using remote satellite imagery for measuring the relative impact of park establishment on forest conservation in this region.