Browsing by Author "Branch, George"

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    An ecological study of the macro-invertebrate fauna of the Eerste River, Western Cape Province, South Africa
    (1982) King, Jacqueline Mary; Branch, George
    The Eerste River is situated in the south-western Cape Province, South Africa. Its upper reaches have a stony substratum, and can be divided into three physical/biotic zones: The Mountain Stream, Upper River and Lower River zones. Investigations of the abundance, biomass, species diversity and species composition of the benthic macro-invertebrates in the three zones were carried out in 1975/76. Spatial and temporal changes in these factors can be correlated with changes in the physico-chemical quality of the water. Abundance and biomass generally increased downstream, but were low below a dam construction-site, because of the blanketing effects of silt on the substratum. Seasonal changes in abundance and biomass differed in the three zones, but always included a peak in spring. The highest values of both were in the Lower River in summer, reflecting the build-up of organic pollutants there during times of low flow. Diversity of the Ephemeroptera, which was felt to be representative of a change in.diversity of the fauna as a whole, generally decreased downstream, with a major drop at the town of Stellenbosch, and another at a sewage-farm outfall. A misleading increase in diversity occurred, however, in the silt-laden waters below the dam site,. due to the fleeting occurrence of individuals of several different species. Composition of the fauna was typical of local rivers with mountain sources. Figures for abundance, biomass and calorific values of species are given in appendices
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    Does the implementation of a closed Fishing Season during the breeding Season benefit a Species? A per-recruit-based approach using Cymbula Granatina as an Illustration
    (2004) Arendse, Clement; Govender, Anesh; Branch, George
    Closed seasons are generally implemented on the presumption that they increase reproductive output of fished populations. This is.based on the assumption that the imposition of a closed season during the breed~· season allows more individuals to reproduce, as they are not being harvested.I evaluated the validity of imposing closed seasons during the breeding season creating a simulation model using the limpet Cymbula granatina as a test case and the compared following four scenarios: 1) an unharvested population; 2) no closed season imposed; 3) a closed season imposed during the breeding season; and 4) a closed season imposed outside the breeding season, to determine the effects of the latter three situations on the reproductive output and yield. From the outputs of the model it was determined that closed seasons do not significantly affect the reproductive output of the population and that the timing of closed seasons made no difference to the reproductive output of the population, as the output was the same for populations with closed seasons during the breeding season or outside the breeding season. Survivors, catch in numbers and yield in biomass were affected by the timing of closed seasons, with higher outputs for each obtained when the closed season was closer to the month when individuals become of harvestable size. It was thus concluded that the imposition of a closed season at any time of the year is an effective management measure if imposing the closed season can reduce annual fishing, but the imposition of a closed season specifically during the breeding season with a view to increase reproductive output brings no benefits relative to closure at any other time of the year. Moreover, any closure will be ineffective if it does not also bring about a reduction of annual fishing effort. The reasons for advocating closure of a fishery during the breeding season are thus based on false ground.
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    A holocene sea surface temperature record in mollusc shells from the South African coast
    (1993) Cohen, Anne Louise; Van der Merwe, Nikolaas; Branch, George
    This thesis describes the construction of a Holocene history of sea surface temperatures in coastal regions of the southern Benguela and eastern Agulhas Bank of South Africa, using marine mollusc shells preserved in archaeological middens. Two independent palaeothermometers were employed: the traditional oxygen isotope technique and a new, alternative technique based on temperature-dependent changes in structure and mineralogy of the shell of a South African limpet species, Patella granularis. The relationship between the isotopic and structural aspects of shell composition, and habitat temperature was confirmed through examination of living populations.
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    Phylogeny and biogeography of Southern African limpets in the genus Siphonaria in the context of a global phylogeny
    (2022) De Coito, Paula Marie; Branch, George; Hedderson, Terry Albert
    Abundant, diverse and ecologically important, the 'false-limpet' genus Siphonaria has a near world-wide distribution. However, arising from uniformity of shell shape among species and its plasticity within species, frequent synonymisations and changes of names have created uncertainty about the number of species that exist and the names that should be applied. In this thesis I pursue three lines of genetic research to address this. First, I resolve the species that exist in two South African complexes: the Siphonaria carbo complex and the S. concinna/oculus complex. Second, I examine what is currently accepted as S. compressa from the only two South African localities where it has been recorded, to determine if the two populations are conspecific. Finally, I compare the genetics of a selection of species from around the world to place the South African species within, and contribute to, a world phylogeny for the genus and analyse geographic patterns of clades emerging from this phylogenetic reconstruction. With respect to the 'S. carbo' complex, Teske et al. (2007), using mitochondrial and nuclear sequence data on Siphonaria nigerrima, S. anneae, and S. tenuicostulata, failed to discern distinct monophyletic lineages, and concluded that these species, together with S. dayi, are different colour morphs of a single species, merged under the name S. nigerrima. This contrasts with a previous systematic revision by Chambers & McQuaid (1994), which considered these to be four separate species. An added complication is that the name S. nigerrima has been synonymised with S. carbo by various authors and in a range of data bases. Using phylogenetic analyses based on COI and 16S ribosomal RNA genes and incorporating additional GenBank sequences of east coast species, I confirm that S. nigerrima and S. dayi comprise a single species, to be merged under the name S. nigerrima because of its priority, and because examination of the type material of S. carbo indicates that it is unlikely that that species is present in South Africa. However, I also show that within the 'S. nigerrima complex' there exist four or possibly even five clades that warrant recognition at a specific level, two of which constitute undescribed and unnamed species (nov. sp. 1 and nov. sp. 2) while the other three can be accommodated under the names S. nigerrima sensu stricto, S. tenuicostulata and S. anneae. Using the same approach, I examined the distinction between S. oculus and S. concinna, which has become blurred in the literature, with only the latter being recognised by Teske et al. (2011). Both my molecular analyses and a consideration of shell features provide evidence that the two are distinguishable and valid species. Siphonaria compressa was first described by Allanson (1958) from specimens found in Langebaan Lagoon on the West Coast of South Africa, where it is associated with the seagrass Zostera capensis. In 2005 a population of what was considered the same species was recorded in Knysna Lagoon on the South Coast. On the basis of COI and 16S analyses coupled with shell morphometrics I found that the two populations have no shared haplotypes and are clearly diverged; IMa2 estimates indicate there has been no migration between these populations and the split between them occurred around 730 000 years ago. Evidence points towards recently expanding populations at both sites. Uni-, bi- and multivariate analyses of 13 morphometric variables revealed that the means for most variables are significantly different and clear differences in shell shape, size and weight exist between the two populations. I thus recognise two geographically delimited species, and in this thesis I distinguish the Knysna population as Siphonaria nov. sp. 3. The fact that the populations are considered separate species has important ramifications for conservation. The third aspect of my thesis was to integrate the southern African species that I now recognised into the most recent global phylogeny of the genus (Dayrat et al. 2014), which focussed strongly on the Indo-West Pacific species and omitted all South African species. I sequenced 120 individuals collected from 51 localities including 11 southern African species - three of which I consider to be undescribed species - and 42 other species from around the world, nine of which were not previously included in any published phylogeny, thus adding a total of 20 species to the global phylogeny. In total, incorporating GenBank sequences, I analysed 272 mtDNA sequences (16S + COI, 1202 nucleotide characters) within a Bayesian framework. Sacoglossans were used as the outgroup as per Bouchet et al. (2017). Similar to Dayrat et al. (2014), two major clades, A and B, were recovered. The South African species were not monophyletic but their positions were clear and distinct and did not influence the original division of the genus into two major clades. The inclusion of the South African species led to a rearrangement of the tree topology, especially within clade A, where all bar one of the South African species were recovered, with the the highly divergent S. serrata occurring in the second major clade B. Within clade A all bar two of the South African species were retrieved in one clade. The exceptions were S. compressa and Siphonaria nov. sp. 3 which fell elsewhere within clade A and were more closely related to Pacific Ocean species. The contents of clade B remained similar to the previously published phylogeny with the exception of a significant rearrangement of the basal species. Although many species remain unnamed, six previously unidentified molecular units in the global phylogeny are identified here and assigned species names. I also explored biogeographic patterns for all recognised species in the genus. There were strong latitudinal trends evident in species richness with high diversity in the lower latitudes, but with a dip at the equator, in contradiction to the prevailing paradigm of greatest diversity at the equator. Species with direct rather than planktonic development had both smaller geographic and smaller average latitudinal ranges. Overall, this thesis encompassed a view of the genus from the small-scale withinspecies population genetics of the highly endangered and range-restricted S. compressa and its sister taxon Siphonaria nov. sp. 3, through the broader geographic delimiting of the species contained within two southern African species complexes, to the placement of all the southern African species within a global context by updating the world phylogeny of the genus.
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    The contribution by phytoplankton, bacteria and detritus to a rocky shore ecosystem
    (1979) Cliff, Geremy; Branch, George
    An investigation has been carried out on the particulate organic matter (IU-1) in suspension over the large inter-- and subtidal reef at Dalebrook in False Bay, standing stocks of hytoplankton, bacteria and detritus were monitored for 13 months, at three localities on the reef, on incoming and outgoing tides. A number of seasonal trends recharge, despite day-to-day variation in t."'1ese stocks. In spring and summer chlorophyll levels were la, 1 - 2 µg/1. Due to the extrerrely lcw nitrate concentrations ( < 2 µg at/1) and to a lesser extent, silicates ( < 6 µg at/1) , little autochthonous phytoplankton production was recorded over this period. Concentrations of nitrates, silicates and chlorcphyll a were highest at the offshore edge of the reef in incoming water. After a strong south-easterly win:i, chlorophyll concentrations of 19 µg/1 were rerorded O, 5 km offshore. Chlorophy 11 concentrations were in the region of 5 µg/1 in winter. Detritus accounted for aln'Ost 80% of the Pa1 and never dropped bela, O, 5 :rrg/1. There were no marked spatial and tidal influences on the mass of detritus in suspension. However, considerable import and export of material is believed to be associated with the strong water m,vements over the reef. Most of the detritus was in advanced stages of deconposition, making it extremely difficult to determine its origin. A Coulter Counter provided particle size spectra over the range 5 - 112 µm. It was found that particles with apparent diameters of 10 - 30 iirn contributed the highest volurre. Bacterial densities ranged fran 4 x 105 to 16 x 105 cells/ml; nurrbers were highest in late surmer and autumn. 95% of the cells were not attached to particles but were free in suspension. These results are canpared with those fran other inshore envirorurents.