Browsing by Author "Omoregie, Edosa"

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    Effects of varying acidic levels on dissolution, strength, organic content ands urface texture of Pacific oysters (Crassostrea gigas) shells
    (University of Namibia, 2016) Omoregie, Edosa; Garises, G.; Liswaniso, G.; Iitembu, J.
    Marine coastal organisms are exposed to periodic fluctuations in sea water pH driven By biological carbon dioxide (CO2) production which may in the future be further exacerbated by the ocean acidification associated with the global rise in CO2. There is widespread concern that these changes have direct impact on coastal organisms and alter the habitats severely. However, little or no attention has been given to the effects of the anticipated decrease in coastal pH on farmed oysters within the Namibian coastal waters. In this investigation, shells of the Pacific oysters, Crassostrea gigas were exposed to varying acidic levels under laboratory conditions; pH level 6.5 represented extreme hypercarpnia condition, 7.0 and 7.5 representing future predicted coastal pH levels. Shell dissolution rate, strength, organic content and surface texture were assessed after a two-week exposure period. Significant loss (p < 0.05) in weight and diameter were observed in shells exposed to 6.5,7.0 and 7.5 pH levels compared to shells in the control groups (pH8.1-8.2). With regard to organic content of the shell, significant reduction (p < 0.05) was only observed in shells exposed to 6.5 and 7.0 pH levels. Microscopic examination of the shell surface revealed reduced nacreous layer while the organic layer of the shells was sheared in acidic conditions. Visual inspection of the nacre region of shells exposed to 6.5 ,7.0 and 7.5 pH showed straight edged tablets, with the nacre regions characterised by sparse with irregular shaped tablets within a reduced organic matrix. Ocean acidification can impact potential changes in morphometry and shell structure of pacific oysters during culture.
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    Lead pollution: A growing concern along the Namibian coastal waters
    (2014) Vellemu, Emmanuel C.; Omoregie, Edosa
    The accumulation of lead within specific strata of the Namibian coastal waters during the winter and summer months (2012) of the Southern Hemisphere was investigated using inductively coupled plasma optical emission spectrometry (ICP-OES). The black mussel, Choromytilus meridionalis was used as indicator organism to ascertain levels of bioaccumulation. Accumulation levels in collected sediments and the water column were used as indicators for the partitioning of lead within the coastal water ecosystem. For this investigation, the Central Namibian coastline was demarcated into four sampling stations (Walvis Bay, Swakopmund, Henties Bay and Cape Cross). Results obtained indicated significantly higher levels of lead in sediment samples collected from the Walvis Bay harbour compared to the other sampling stations (p < 0:05), with Cape Cross and Henties Bay relatively in a more pristine stage in terms of lead pollution. Although not significant (p > 0:05), worrisome levels were observed in C. meridionalis tissues collected from Walvis Bay harbour. Maximum mean values of lead detected in sampled C. meridionalis collected from the Walvis Bay harbour was 0.70 mg/Kg of sample dry weight during the summer months. The mean values within the sediments ranged from 79.30 to 0.30 mg/Kg detected from the Walvis Bay harbour to Cape Cross respectively. Though C. meridionalis farmed in and around Walvis Bay harbour could be regarded safe for human consumption as observed lead levels did not exceed permissible WHO limits. However, industrial activities involving discharges of untreated effluent into the harbour could pose health concerns over the long term if these practices are not checked. The major outcome of this investigation is the need for continued monitoring of activities in and around the Walvis Bay harbour that could aggravate increased lead pollution to avoid human risks and irreversible ecosystem destruction.