Browsing by Author "Olivieri, Emilia T"

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    Colonization and succession of phytoplankton species in upwelling plumes off the Cape Peninsula
    (1981) Olivieri, Emilia T; Hay, C
    Colonization and temporal changes in phytoplankton diversity and biomass in the upwelling plumes off the Cape Peninsula are described for two different communities. A drogue study showed the presence of a fast-developing mixed phytoplankton community with Chaetoceros compressus Laud. and Skeletonema costatum (Grev.) Cleve the dominant species. Monthly transect studies, however, revealed the presence of another community consistently dominated by Nitzschia spp. Species succession did not occur in either phytoplankton community. Factors Likely to affect the development of the phytoplankton communities and cause differences in certain community characteristics, e.g. dominance, biomass and diversity, were attributed to differences in: ( 1) the origins of the source water; (2) the wind speed and direction; and (3) the sampling strategies employed. The factors responsible for the successful colonization of the different species in the phytoplankton community were thought to depend on: (1) the initial variations in species diversity and abundance of the seeded population in newly upwelled waters; (2) the extent to which the upwelled waters mixed with neighbouring waters; and (3) the specific selective adaptations for growth of the individual species. Possible adaptive phytoplanktonic mechanisms in a changing environment, were discussed in terms of cell size, growth, nutrient absorption and buoyancy.
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    Phytoplankton growth and zooplankton grazing in the southern Benguela current
    (1985) Olivieri, Emilia T; Griffiths, Charles L
    The development and production of several phytoplankton communities and the consumption of these communities plankton were investigated in newly by herbivorous mesozooupwelled waters of the southern Benguela Current by means of an electronic counting and sizing technique (Coulter counter). A feasibility study was initiated to test the accuracy of the Coulter counter (Model TAII) in estimating phytoplankton size and biomass in fresh and preserved samples from the Benguela current. Counting phytoplankton using this method gave a higher degree of reproducibility than the inverted microscope method. Certain recommendations as to the counting procedures were made. The counting of preserved samples was shown to introduce artefacts, resulting in a 77 per cent reduction in particle volume after a year of preservation. Correlations of particle volume with chorophyll a, carbon and nitrogen were calculated, with highest correlations occurring between particle volume and chlorophyll a. Particle volume was shown to represent biomass as accurately as any of the other methods.