Browsing by Author "Ewart-Smith, Justine L"

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    Grazer control on benthic algae in the Berg River, Western Cape, South Africa
    (2011) Basic, Dunja; Ewart-Smith, Justine L; Day, Jenny
    Benthic environments in streams are areas of high biological activity where primary producers and consumers interact with each other and the environment. Various factors such as light, nutrient availability and temperature affect algal biomass accumulation however disturbance factors and grazing lead to biomass losses as well as changes in the species composition and densities of algae. There are little, if any, studies done on the effects of grazers on benthic algae in South African rivers and as such, this experiment was done in the Berg River, in the Western Cape of South Africa. The aim was to ascertain the effects of herbivores on benthic algae within the river and lit was hypothesized that periphyton biomass would be higher where grazer densities were lower and that the differences observed in biomass of periphyton between treatments would increase over time. It was also hypothesized that there would be a lower diversity of algae where there were lower herbivore densities. A randomized block design experiment was set up in the Berg River and treatments of 'excluded herbivores' and 'included herbivores' were set up, with two pairs of each treatment spread across four replicates. Stones from the stream were randomly selected and placed in the boxes. After five days half of the boxes were sampled and after eight days, the remaining half was sampled. Stones were scrubbed to remove periphyton from the stones and a sub-sample of 50ml was removed from each for later algal species identification. Invertebrates were removed from the boxes, preserved in ethanol and later identified to family level. Chl-a and AEDW (mg/m²) were determined from the samples as were invertebrate and algal densities. The results showed that there were no herbivore density effects on biomass most likely due to the season of sampling and the length of the experiment. However, the effect on algal densities was more pronounced as there was a higher variety of algal forms present where herbivore densities were lower. To get a better idea of how herbivores affect periphyton other factors need to be taken into account like experimental time period, season and different environmental conditions.
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    The relationship between periphyton, flow and nutrients in foothill rivers of the south-western Cape, South Africa
    (2012) Ewart-Smith, Justine L; King, Jackie; Day, Jenny
    This thesis examines spatial and temporal patterns in periphyton community composition and biomass and the environmental factors responsible for shaping these communities in south-western Cape rivers. The study focused on two prennial foothill rivers in the south-western Cape: the Berg River, which is oligotrophic but has a large dam (The Berg Dam) situated in its upper reaches; and the Molenaars River, which has a natural flow regime but is moderately enriched by trout farm effluent. Two site on the Berg River (one upstream and one downstream of the Berg Dam) and two on the Molenaars River (one upstream and one downstream of the Du Toit's Kloof trout farm) were used to study temporal dynamics in periphyton communities over a 21-month period between September 2007 and May 2009.