Browsing by Author "Hay, C"

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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 production studies in the coastal waters off the Cape Peninsula, South Africa
    (1980) Brown, Penelope Cranstoun; Field, John G; Hay, C
    Procedures for measuring phytoplankton production in the southern Benguela upwelling region were investigated. A 125 ml incubation bottle is recommended for routine primary production measurements. Exposure of production samples to high light intensities during manipulations on deck was found to inhibit rates of production near the bottom of the euphotic zone particularly below a thermocline. Simulated in situ rates of oxygen production were only slightly higher than in situ rates. When ships time is limited, the simulated in situ method can safely be used in local waters. Definite diel periodicity in rates of production at the sea surface was demonstrated and appears to be linked to light levels and nutrient concentrations, as well as to the ratios of light to dark hours. Since diel variation probably decreases with depth, its effect on integrated daily production is reduced. Nevertheless, the time of incubation should be chosen to minimize the effect of periodicity on daily production estimates. The period spanning noon is recommended for local use. Changes in phytoplankton production and biomass are linked with physical and chemical changes in the upwelling system off the Cape Peninsula. Extremely active upwelling was found to limit primary production and from these measurements the annual net primary production in the Cape Peninsula upwelling region is estimated for the first time to be approximately 1.13 kgC.m⁻ ³.y⁻¹.