Bibliography: leaves 142-158.

Includes bibliographical references (p. 109-121). / The aim of this thesis is thus to explore and describe any ecosystem-level changes that may have occurred since fishing and exploitation began in the Benguela, in terms of both structure and function. This will be investigated using Ecopath with Ecosim (EwE) There are currently available, models of the Benguela ecosystem based on modern catch and biomass data that cover the period from the 1970, or '80s, until the 2000s (Shannon et at., 2003; Heymans et al., 2004, Roux & Shannon, 2004).

Includes abstract. / Includes bibliographical references (leaves 69-81). / Phenotypic analyses of sibling species provide the opportunity to examine divergence that is caused by adaptation rather than phylogenetic history. Rhinolophus capensis and Rhinolophus swinnyi diverged from a common ancestor between 15 and 20 million years ago. The Fynbos biome of the south-western Cape (South Africa) arose around the same time, and its distribution is coincident with that of R. capensis. Since this event probably influenced the speciation of these species, I examine differences in the ecomorphology of these bats in their current distributions. R. capensis is bigger than R. swinnyi, with corresponding differences in echolocation call signatures and wing morphology.

My thesis combined an observational study and field and laboratory experiments to investigate how nutrients and bioturbation by C. kraussi interact to structure macrofaunal communities and how ambient temperatures influence these factors.

Bibliography: leaves 74-78. / Saldanha Bay, which lies on the west coast of South Africa, has undergone major development over the last 30 years, including breakwater and harbour construction, harbour extension, dredging, mining, fishing, fish-processing and mussel culture. The aims of this study were to determine whether the benthic macrofaunal communities in the Bay have been altered over this period and to explore the benthic community patterns within the Bay prior to and after harbour development.

Includes bibliographical references (leaves 49-61). / During the International Geophysical Year, 1957 - 1958, it was decided that the hydrographic frigate, S.A.S. "Natal", as part of the South African contribution, should undertake a number of oceanographic cruises off the east and south coasts of the Republic of South Africa. Thus during 1958 three cruises were carried out in February and March, May, and August, during which a. total of eighty-four oceanographic stations were occupied. Sixteen were occupied in the first cruise and thirty-four each in the second and third cruises. The stations were located on "lines" normal to the coast at Durban, Port Shepstone, Port St. Johns, Bashee River, East London, Kowie River, Port Elizabeth, and Cape Seal. In the first cruise only four lines were worked and of these, the first three contained three stations each while the fourth (Port Elizabeth line) contained six stations. The first station (NGY.1) was not located on any line and was used for gear testing. In the second and third cruises the minimum number of stations per line was increased to four while the number on the Port Elizabeth line remained at six. At each station both biological and hydrological sampling was carried out. The zooplankton samples were sorted into major taxonomic groups (e.g. Hyperiid amphipods) in the 1aboratory,after determination of the settled- and displacement volumes in the case of samples collected with N.70 nets. It is this.materia1 that formed the basis of this study. The investigation was undertaken with the following a1ms in mind: (i) To further the knowledge of the Hyperiid Amphipoda present in the waters off the east and south coasts of the Republic. (ii) To extend the knowledge. of the world geographic distribution of' hyperiids and clarify the position regarding the alleged cosmopolitan status and wide tolerances of many species. (i1i) To define more precisely the hydrological tolerances of hyperiid amphipods and assess ·their value as "indicator species", either alone or in association with other hyperiids or members of other taxomomic groups in the zooplankton. (iv) To determine the extent to which similar hydrological tolerances govern interspecific association in the hyperiids.

This thesis investigates the patterns of distribution and migration of the adult and recruit shoals of anchovy Engraulis capensis off Namibia and the environmental factors most important to such distributions and migrations. It also examines anchovy feeding patterns. The distributions of anchovy shoals in summer months were recorded during extensive, acoustic surveys along the whole Namibian coastline from November 1978 to March 1982. A purse-seine fishing vessel was used to identify the shoals detected. Winter surveys of selected parts of the coastal waters recorded shoal distribution and sampled the fish and environmental factors associated with the densest shoal groups. Shoal groups were followed for periods in excess of 24 hours and sampled at 4-hour intervals. Winter distribution, length and age composition were also obtained from the commercial fishery statistics. Stomach contents extracted from samples of anchovy shoals were compared to water samples from their environment. Data on diet obtained from the fishery catch statistics are analysed to indicate feeding trends.

This thesis forms part of a multi-disciplinary study of the Bot River estuary, situated between Kleinmond and Hawston on the southwest coast of the Cape Province, and falls within the framework of the investigation of all Cape estuaries, initiated by SANCOR and co-ordinated by the Estuarine and Coastal Research Unit of the CSIR. The motivation for the research program on the Bot River estuary, in particular, was the need to obtain detailed knowledge of its dynamics in order to be able to address its unique management problems.

Includes bibliographical references (leaves. 23-28). / The frequency and geographical range of hannful algal blooms (HABs) are believed to be on the increase, with adverse affects on marine and human health making the implementation of stringent controls governmg monitoring programmes commonplace. The South African monitoring programme was established in 1989 and relies upon microscopic identification of HAB species. Microscopic identification is labour-intensive, requiring a high level of taxonomic expertise, and could be considered impractical for routine monitoring where analysis of large numbers of samples is required. Novel monitoring techniques, focusing mainly on probe technology, are being developed for rapid, unequivocal identification and enumeration of HAB species. In this study, a triplex peR assay, incorporating a genus-specific ribosomal DNA primer designed from phylogenetic studies on local Alexandrium populations, was optimised for application to environmental samples and tested against natural assemblages containing Alexandrium minutum. Specific positive results were consistently generated for samples containing A. minutum. Samples absent of A. minuturn cells did not generate the Alexandrium-specific amplicon. The absolute detection limit of 440 A. minutum cells r1 for this assay was established. Effects of non-target cells on the sensitivity of the assay were also investigated: although a decrease in sensitivity was found, A. minutum cells could still be detected in the presence of 100 times more non-target cells. This assay has been shown to be a useful tool for unequivocal identification of A. minutum cells within local environmental samples.

Bibliography: leaves 78-95. / Experiments were carried out during a cruise in the southern Benguela upwelling region in April 1989 to budget the nitrogen flux through the different microplanktonic compartments leading to copepods. Uptake of nitrate and ammonium by three different size classes of phytoplankton (net-, nano-, and picoplankton) was measured using ¹⁵N isotope techniques. Microzooplankton grazing on autotrophic picoplankton and nanoplankton was quantified by predator:prey dilution experiments. Between 7 and 52 copepods in species assemblages representative of the natural communities were incubated in 11 samples of ambient seawater to examine grazing rates on chlorotic and non-chlorotic microplankton. Copepod and microzooplankton excretion rates were also measured using ¹⁵N isotope techniques. Two experiments were performed at night and two during the day. Nitrogen uptake and regeneration studies revealed that phytoplankton of all size classes showed a consistent preference for ammonium, although nitrate was quantitatively more important for netplankton. Microzooplankton excretion fulfilled most of the phytoplankton ammonium demand, while copepod excretion was only detectable at night. Competition between microzooplankton and mesozooplankton for phytoplankton prey was minimal, in that the former appeared to graze mainly < 2 μm phytoplankton. Nevertheless, microzooplankton grazers had a significant impact on phytoplankton standing stocks. Microzooplankton grazing rates represented about 5 % of phytoplankton biomass under diatom bloom conditions and an average of 46% under post-bloom conditions. On the other hand, copepods removed 18% of phytoplankton biomass under bloom conditions and only 1 % under post-bloom conditions. Copepods appeared to demonstrate a preference for protozoan prey over phytoplankton, in that the percentage of carbon ingested as protozoans exceeded the percentage of carbon available as protozoans. Quantitatively, protozoans made up a highly variable component of the copepod diet. For example, at station 12, where the plankton assemblage was dominated by oligotrichous ciliates, 80 % of the ingested nitrogen ration consisted of protozoa. However, the total ingested ration at this station was only 0.6% of that at station 2, with a bloom assemblage, and it is unlikely that such a diet could support a large production potential. On average only 3 % of the nitrogen ingested by protozoa was subsequently transferred to copepods. Microbial pathways thus appear to have a minor role in the· transfer of nitrogen to higher trophic levels, their function being mainly the regeneration of nitrogen for primary producers.