The factors controlling primary production in the Southern Ocean were investigated over two years during two cruises of the South African National Antarctic Program (SANAP). The first cruise was conducted to the region of the eastern Atlantic sector of the Southern Ocean during the collaborative Scandinavian/South African Antarctic expedition conducted in austral summer (DecemberIFebruary) 1997-1998. Production studies were conducted in the vicinity of the Marginal Ice Zone (MIZ), Interfrontal Zone (IFZ) and Antarctic Polar Front(APF). The second cruise was conducted during the Third Marion Island Oceanographic Survey (MIOS III) to the region of the Sub-Antarctic Prince Edward Islands in austral autumn (April/May) 1998. Size-fractionated production rates were estimated by 14C incorporation using standard JGOFS protocols. Oceanographic data from the first cruise suggest that the three regions can be divided into two distinct regimes. Stations occupied in the vicinity of the MIZ and the APF were characterised by a shallow mixed layer depth « 40m) while at the IFZ-stations, the mixed layer depth exceeded the 1% light depth. Microphytoplankton dominated integrated chlorophyll-a biomass in the MIZ (total chlorophyll a ranged between 15.4 and 41.3 mg Chi-a. m-2) and at the APF (range between 10.7 and 31.4 mg Chi-a. m-2) , comprising > 50% of total chlorophyll-a at all these stations. Xl Within the IFZ (2 stations), nanophytoplankton dominated total integrated Chl-a biomass (range between 5.6 and 8.8 mg Chi-a. m-2) comprising, on average, 36% of the total. Picophytoplankton comprised an average of 12% of the total Chl-a biomass (range between 3.1 and 5.9 mg Chi-a. m-2) in the MIZ, 36% in the IFZ (range between 6.4 and 7.8 mg Chl-a . m-2) and 20% in the vicinity of the APF (range between 6.8 and 10.6 mg Chi-a. m-2). Total integrated primary production ranged between 316 and 729 mg C . m-2. d-1 at stations occupied in the vicinity of the MIZ, and between 292 and 317 mg C . m·2• d-l within the IFZ. At stations occupied in the region of the APF, total integrated production ranged between 708 and 926 mg C . m-2• dol. The contribution of various size fractions to total productivity generally displayed the same pattern as integrated Chl-a biomass. Microphytoplankton formed the most important contributor to total production at stations occupied in the MIZ and at the APF. Within the IFZ, nanophytoplankton dominated total daily production. Nutrient data suggest that concentrations of macro nutrients within the upper water column were above the threshold where growth would be limited. Preliminary results showed that concentrations of iron (Fe) were highest in the southern region of the MIZ and in the vicinity of the APF. During the second cruise, conducted in the vicinity of the Sub-Antarctic Front (SAF) and in the upstream, inter-island and downstream regions of the Prince Edward Islands, there was evidence of fresh water run-off from the islands, (i.e. decreased salinities and increased concentrations of ammonia and nitrate). Oceanographic data collected at the various production stations indicated that the upper water column was well mixed throughout the survey. Total integrated biomass during the study ranged between 8.5 and 20.1 mg Chi-a. m-2• No distinct patterns in total Chl-a biomass were evident. Picophytoplankton dominated total biomass comprising> 45 % of total pigment at all stations. Nanophytoplankton were the second most important contributor to total integrated biomass. Generally xu microphytoplankton contributed < 10 % of total ChI-a. Total daily integrated production was highest (442.6 mg Chi-a. m-2) at the single station occupied in the vicinity of the SAF. Outside this region, total areal production was lower, ranging from 94.5 to 353.0 mg C . m-2. d-1. With the exception of the station occupied in the vicinity of the SAF, total productivity was dominated by nanophytoplankton, which comprised between 48 and 66% of the total. Concentrations of macronutrients did not appear to be limiting to phytoplankton growth. The absence of a phytoplankton bloom in the vicinity of the islands appears to have been related to water column stability, which was influenced by the prevailing oceanographic regime during the survey. Previous studies have shown that when the SAF lies in close proximity to the islands, advecting forces prevail, resulting in the islands functioning as a flow-through system. During this study, the SAF lay immediately north of the islands. As a consequence no water was trapped in the leeward side of the islands. The results of the two cruises suggest that phytoplankton production in the four systems investigated: the Marginal Ice Zone (MIZ), Antarctic Polar Front (APF), Inter Frontal Zone (IFZ) and Prince Edward Islands (PEl), was largely controlled by water column stability. It is probable that the availability of iron, particularly in the region of the MIZ and APF, may have further contributed to the elevated production recorded in these two regions.

Diel patterns of nitrogen (NO₃⁻, NH₄⁺, urea) uptake were investigated in natural assemblages of phytoplankton from neritic and oceanic environments off the coast of British Columbia. This is the first study to report nitrogen uptake rates and extensive measurements of ambient NH₄⁺ and urea concentrations in these waters. Calculated rates of N uptake, 15 based on ¹⁵N incorporation into particulate matter during time course experiments, were maximal during the day and minimal at night. Besides the obvious effects of irradiance, the amplitude of the periodicity in uptake rate was influenced by phytoplankton community composition, ambient nitrogen concentration, forms of nitrogen available, and depth of sampling. Uptake of nitrogen during the night and in artificial darkness were measurable proportions of daytime and light uptake rates, with the importance of dark uptake generally increasing with increasing N limitation. This is the first study of diel urea uptake by marine phytoplankton in the field. The ratios of dark to light urea uptake over a diel cycle were more similar to those of NO₃⁻than those of the other reduced N form, NH₄⁺. Rates of NO₆⁻ and urea uptake by phytoplankton in the shallow and deep chlorophyll layers of the Strait of Georgia were measured over a gradient of irradiances and results of these experiments could be fitted with a hyperbolic function similar to the Michaelis-Menten equation. Half-saturation constants (KLT) for light-dependent uptake of urea and NO₃⁻ ranged from 0 to 14% of the surface irradiance and dark uptake was a variable, but often substantial (> 50%) portion of the total (light + dark) uptake. The uptake response of nitrate-replete and -starved populations of the picoflagellate, Micromonas pusilla (Butch.) Manton et Parke, to urea, NH₄⁺ and NO₃⁻ perturbations was determined by both ¹⁵N accumulation and nutrient disappearance from the culture medium. Maximum specific uptake rates (Vmax) of NH₄⁺ were 0.13 h⁻¹, more than 2 times the Vmax of NO₃⁻ or urea (ca. 0.05 h⁻¹). The half-saturation constants (Ks) for urea, NH₄⁺ and NO₃⁻ were within ± 0.1 µg-at N•L⁻¹ of each other; the average value of 0.41 µg-at. N•L⁻¹ is within the range reported for small, oceanic diatoms. NO₃⁻ uptake was completely inhibited following NH₄⁺ addition (1-10 µg-at. N•L⁻¹), whereas urea addition resulted in only a 28% reduction in NO3- uptake. Starved cultures of M. pusilla exhibited variable uptake of NH₄⁺ and urea as a function of time, with an initial "surge" uptake response. This is the first laboratory study of N uptake by an eucaroyotic picoplankter and demonstrates that many of the transient uptake responses reported for diatoms, with which it competes in the field, are common to this picoplankter. Diel periodicity of nitrogen uptake and assimilation were measured in N-replete batch cultures of M. pusilla and also in N-limited cyclostat cultures (14L:10D) at three growth rates corresponding to ca. 75, 50 and 25% of it's maximal growth rate. Nitrate uptake was continuous and independent of the L:D cycle in the cyclostat cultures at the lowest dilution rate, but NO₃⁻ uptake rates exhibited pronounced periodicity in the batch and higher dilution rate cultures, a response similar to that seen in previous studies of cyclostat cultures of some diatoms. Diel patterns in cell division, mean cell volume, potential uptake rates and internal pools of NO₃⁻ were also observed and are discussed with respect to the nutritional status of the cells. The effect of irradiance on the uptake of NH₄⁺ and NO₃⁻ by M. pusilla was also described by Michaelis-Menten kinetics; with increasing N limitation the importance of light for nitrogen uptake decreased and dark uptake increased from 5-20% to 21-39% of NO₃⁻ and NH₄⁺ uptake rates, respectively, at saturating irradiance. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Laboratory and field experiments measured urea uptake and assimilation with ¹⁴C⁻ and ¹⁵N-urea and by disappearance of dissolved urea. A modified diacetyl monoxime method was developed, which accurately and precisely determined dissolved urea concentrations in seawater. In the Strait of Georgia, chlorophyll α (chl α) specific uptake rates of ammonium (NH₄⁺) and urea were greatest in stratified water; whereas, chl α specific uptake rates of nitrate (NO₃⁻) were greatest in frontal water. Ammonium and urea regeneration rates were calculated by a mass balance method and the rates were similar. Differences between measurements of particulate nitrogen, dissolved NH₄⁺, NO₃⁻ and urea, and ¹⁵N uptake were used to explain the dominant N transformations in frontal and stratified seawater. Uptake rates measured by ¹⁴C-urea were ca. 1.4 times faster than those determined by ¹⁵N-urea in the Sargasso Sea. Turnover times of urea in the surface-mixed layer were ca. 12 h. Within some seawater samples, phytoplankton utilized urea at rates which approximated the maximum rates of utilization. In a nitrate-sufficient culture of Thaiassiosira pseudonana (clone 3H) (Hustedt) Hasle and Heimdal, urea uptake rates measured by three methods disagreed; whereas, no discrepancies occurred in a nitrate-starved culture. NH₄⁺ was released from cells after urea was taken up and was later reabsorbed. A model of urea uptake and assimilation by T. pseudonana is proposed. An obligate selenium (Se) requirement for growth of T. pseudonana was demonstrated in axenic culture in artificial seawater. The addition of 10⁻⁹ M SeO₃²⁻ to culture medium was sufficient for good growth of this alga; SeO₄²⁻ was only effective at concentrations greater than 10⁻⁷ M. To elucidate the biochemical role of Se in T. pseudonana, cells were cultured in medium containing 10⁻⁹ M Na₂ ⁷⁵SeO₃. Two soluble polypeptides of 21 and 29 kD contained ⁷⁵Se. Glutathione peroxidase was detected on non-denaturing polyacrylamide gels and ⁷⁵Se co-migrated with the enzyme. It was concluded that Se is an essential element for growth of T. pseudonana due, in part, to the presence of the selenoenzyme glutathione peroxidase. / Science, Faculty of / Botany, Department of / Graduate

No description available.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / Aquaculture is a growing industry in South Africa, with the production of abalone, Haliotis midae, at the forefront. The Western Cape Province hosts 12 of the 18 abalone farms in South Africa, with a concentration of farms in the Walker Bay region of Hermanus and Gansbaai. Walker Bay is situated on the western side of the Agulhas bank, which allows warm water from the Agulhas current, as well as cold water from the Benguela current to mix. This area experiences seasonal upwelling pulses in summer, which provide the environment with a high nutrient load. This encourages the prevalence of harmful algal blooms (HAB) that can consist of toxin-producing dinoflagellate species. These species have the ability to kill organisms in the nearshore. This poses a problem for aquaculture farms situated in the area, where HAB events have caused the death of millions of abalone and has decreased productivity of farms in previous years. Farms therefore need to implement stringent phytoplankton monitoring schedules, as well as develop better filtering methods to reduce the density of phytoplankton that may flow into the farm. This study aimed to understand the phytoplankton community assemblages that may be pumped into an abalone farm (Abagold Ltd) over a 16 month period. This was achieved by investigating how phytoplankton community metrics such as abundance, species diversity, richness and evenness fluctuated over a 16 month time period. The frequency of HABs were investigated, comparing the peaks of blooms and how they differed between seasons and the subsequent impact on monitoring activities by the farm until the bloom passes. Secondly, a study was done to determine the efficiency of drum filters to reduce the density of phytoplankton cells from the water that is sourced from the ocean and pumped through the farm. Phytoplankton community assemblages were sampled and identified to genus level, and species level when possible, once a day for 16 months, from September 2018 to December 2019. As the risk of potential HAB formation rises, the number of sample collections increased to assist in the decision making process of the operational manager of the abalone farm to mitigate negative impacts originating from HAB events. The species richness, Shannon-Weiner diversity index and Pielou’s index of evenness were calculated. The number of phytoplankton samples collected each day were tallied to understand the change in monitoring frequency with regard to HAB abundance. Phytoplankton community samples were collected before and after a 15 μm drum filter during bloom events, after which the densities were then compared. The peak mean monthly cell density occurred in late early autumn of 2019 (March: 721 179 ± 226 473 cells/l). During this time, the diversity (Shannon-Weiner Index) of species was lower than that of mid spring and this trend is supported by literature, where a decrease in diversity occurs with an increase in HAB density. The relative abundance of species was calculated to quantify the dominant species present

No description available.

No description available.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2004. / Restricted until May 2005. Bibliography: leaves 220-230.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 200-219).

Thesis (Ph.D.)--Flinders University, School of Biological Sciences. / Typescript bound. Includes bibliographical references: (leaves 149-166) Also available online.