Thesis (degree (Master in Technology))--Cape Technikon, Cape Town,1996 / Red tides are a common feature of the southern Benguela upwelling system and are usually dominated by migratory flagellates and the ciliate Mesodinium rubrum. Seasonal blooms of dinoflagellates occur in response to seasonal upwelling and typically succeed diatom blooms. High biomass, multispecies red tides result from concentration by various physical forces and are characteristically found in warm, stratified, nutrient-depleted water overlying cold, nutrient-rich bottom water. The influence of turbulent mixing, light and the availability of nutrients on the migratory behaviour of red tide species was studied by means of both mesocosm and field studies. The mesocosm experiments were conducted in a 3m laboratory column in which a red tide community, collected from the field, was introduced above nutrient-rich bottom water. All the dominant species exhibited directed vertical migration, with ascent and descent starting before sunrise and before sunset respectively. Observations support the hypothesis that red tide organisms can sustain high concentrations in nitrogen depleted surface waters by growing at the expense of nitrate taken up during nocturnal descent. Vertical niche separation of different red tide species was evident both during the night and the day. Observations support the hypothesis that species are capable of coexisting within a red tide bloom. Division rates were determined from the frequency of paired nuclei and cells. C. furca recorded the highest growth rate (u = 0.24). The relatively low growth rates emphasise the importance of physical processes, as opposed to biological processes, in the formation of red tides within upwelling systems.

Thesis (M.Tech.)--Cape Technikon, 1996. / Bibliography: leaf 111-121. Also available online.

Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2008. / Committee Chair: Kubanek, Julia; Committee Member: Hay, Mark; Committee Member: Jiang, Lin; Committee Member: Pavia, Henrik; Committee Member: Snell, Terry.

The species composition of planktonic communities is determined not only by abiotic factors, such as nutrient availability, temperature, and water column stratification but also by biotic interactions between hosts and parasites, predators and prey, and among competitors. Blooms of the red tide dinoflagellate, Karenia brevis, can dramatically alter the planktonic community, reaching densities of millions of cells per liter and occurring nearly monospecifically. I investigated whether K. brevis uses chemical compounds to defend against grazing or to inhibit the growth of competitors. Because K. brevis is known to produce brevetoxins which act as potent neurotoxins in mammals, I also investigated whether brevetoxins played a role in competition or predator resistance. Experiments revealed that copepods fed diets rich in Karenia brevis experienced lowered fitness, however, nutritional inadequacy, rather than toxicity, was responsible for the decrease in grazer fitness. Compounds exuded from natural samples of K. brevis blooms did, however, inhibit the growth of four of five model competitors. Compounds exuded from K. brevis cultures were similarly allelopathic to competitors. Exposure to these allelopathic compounds resulted in lowered photosynthetic efficiency of all competitors, and decreased cell membrane integrity of three competitors. The allelopathic potency of K. brevis blooms was variable between collections and years, but allelopathy did not correlate with bloom density or concentration of brevetoxins. However, the variability of allelopathy could partially be explained by the presence of specific competitors. The diatom Skeletonema costatum reduced the growth-inhibiting effects of K. brevis bloom exudates, suggesting that S. costatum has a mechanism for undermining K. brevis allelopathy. Allelopathic compounds exuded by K. brevis that inhibited the growth of the diatom Asterionellopsis glacialis were partially characterized. K. brevis produced multiple, polar, organic compounds that inhibited A. glacialis growth. Exuded brevetoxins, on the other hand, had no effect on A.glacialis growth. Taken together, these results indicate that K. brevis is not chemically defended against grazing, but does produce yet-unidentified allelopathic compounds that inhibit the growth of competing phytoplankton. Blooms of K. brevis may be facilitated by the exudation of potent allelopathic compounds, but the specific phytoplankton assemblage has the potential to alter bloom dynamics.