Includes bibliographical references.

Targeting marine diamondiferous deposits along the south-western Namibian coastline has involved the construction of seawall berms to advance the coastline and permit mining in previously subtidal areas. Large areas are mined out to bedrock level by the removal of overburden (sand and gravel), and after mining is complete, areas behind the seawalls fill with seawater, creating a series of coastal marine ponds that have the potential to function as saline wetlands corresponding to closed estuaries. The study site lies north of the Orange River mouth, within the Tsau//Khaeb (Sperrgebiet) National Park, to which the public has restricted access due to diamond mining in the area. Consequently, there is a focus on biodiversity conservation and the overall objective of this thesis was to determine the ecological value of the mining ponds by investigating whether they harbour sufficient biodiversity to qualify as a viable alternative ecological habitat, rather than restoring them to their original state as backfilled, revegetated dune areas. The study area, approximately 75 kilometres in length, was divided into north, middle and south sections, according to the age and status of mining activities, and I first assessed whether ponds in these three areas differed in their physical properties (Chapter 1). To determine whether the ponds serve as a useful ecological role worth preserving, I then investigated the diversity and amount of saltmarsh vegetation (Chapter 2), bird species (Chapter 3) and fish (Chapter 4) currently benefiting from these mining ponds. Ponds in the north are older and hypersaline whereas the south and middle ponds are younger and closely approach physical conditions in the sea. Diurnal fluctuations in oxygen concentration took place, but oxygen levels never dropped below 80% and were thus not limiting. After about 15 years, ponds developed salinities in excess of 80‰, which is likely to set limits on their ecological viability. Most ponds supported saltmarshes, but only a single species, Salicornia natalensis, grew around them. Its abundance was greatest around old ponds, but its health decreased with salinity. Wind emerged as a likely means of dispersal among ponds. The ponds supported a rich avifauna, averaging 11028 birds per count for all ponds combined; 36 species were recorded, ten being endemics, and five being listed in Namibia's Red Data Book. Numbers were highest for ponds that were being ‘dewatered' to remove water prior to mining, as this exposed a rich benthic epifaunal source of food. Blacknecked Grebe, Cape Cormorant, Greater and Lesser Flamingos, Kelp Gull and Common Tern were the most abundant birds. Salinity did not limit bird numbers or diversity, so the northern high-salinity ponds may continue to serve as bird habitat for periods of time much greater than the 15 years after which they become hypersaline. In comparison with nine other wetlands in the region, the ponds had great numbers, diversity, densities, and numbers of threatened species than about half of these wetlands, many of which are considered Important Bird Areas (IBAs). In many cases, they also supported more species that had numbers in excess of 1% of the southern African population than these IBAs. Only two species of fish commonly occurred in the ponds, the west coast steenbras Lithognathus auratus and the southern mullet Chelon richardsonii, although small numbers of two other marine species were recorded. The diversity of marine fish was thus low, even by the impoverished standards of west-coast estuaries. Unexpectedly, there were no significant differences between the ichthyofauna of ponds in the north, middle and south, nor was there any relationship between total fish numbers and salinity. Body condition of steenbras was lowest in the hypersaline north ponds, and their stomach contents contained a low diversity of food items there. The presence of recruits and the range of gonadal states suggested that both species bred in the ponds. Steenbras proved to be protandrous, with females dominating larger size classes. Growth rates of both species were faster in the ponds than in the adjacent sea, and mullet achieved substantially greater sizes in ponds. Thus, the ponds do serve as viable ecosystems, albeit with a limited range of saltmarsh and fish species, and support an impressively diverse avifauna. Their long-term viability will, however, become limited by rising salinity as their age increases.

As stated by Stephen Harris, a mere 30 years ago, the idea of commercial cyber-attack was rather a topic for the science fiction novelists than reality.' However, nowadays we witness a growing tendency of reoccurrence of this phenomenon across many sectors that rely on progressively advancing technology. Despite always being known as a conservative field, the maritime industry is no exception in terms of the exposure to risks that result from cyber-attacks.

Includes abstract. / Includes bibliographical references. / The overall aims of the thesis were to assess spatio-temporal change in macro species assemblages at sites located around the South African coast. Detected changes were considered in parallel with regional patterns of bioinvasion and climate change driven shifts in temperature trends over comparable time scales.

The second half of the twentieth century has brought drastic changes in technology. These advances have changed the way marine resources are harvested or acquired The development of SCUBA made diving to depths of 50m unrestrained by the need for surface support, feasible. 1 This opened up the possibility of exploring below the surface of the sea. It also brought with it the possibility of salvaging wrecks and remains which had been hidden since antiquity.2 The year 1954 saw the first stem trawler the Fairtry converted from a decommissioned whaler. She was to set the standard for trawling efficiency and her design was soon replicated, replacing other types. 3 Nylon fibres made lines and nets lighter and more durable.

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Bibliography: pages 135-146. / 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.

Includes bibliographical references. / Ecklonia maxima and Ecklonia radiata are both kelp bed forming macroalgae along the South African coast, and the latter is also found in considerable abundance in Australia and New Zealand. Genetically they exist as two distinct species and can usually be differentiated morphologically, especially when occurring as geographically separate entities. However, they do appear to intergrade when growing together, where plants of apparent intermediate and indeterminate morphology have been observed. This study tested the reliability of morphology in separating these two Ecklonia species across their intraspecific range of morphological variation, from locations where the species co-occur, as well as where they appear in isolation in South Africa (both species) and Australia (E. radiata only). No individual characters reliably separated between species, yet overall size distinctions as well as the morphometric separation of hollow and solid-stiped sporophytes provide good evidence for morphological differentiation of E. radiata and E. maxima. While E. radiata clusters morphometrically, a distinction between Australian and South Africa specimens is observed. In localities where the two species are reported to co-exist morphological distinction is less clear, particularly in deep water at Buffels Bay. The blade morphology of these deep water sporophytes is distinct from both E. radiata and E. maxima across all locations, while overall size distinctions contribute most prominently to the morphological separation of E. radiata and E. maxima at De Hoop. Environmental data in combination with more detailed genetic analyses, especially those aimed at hybrid identification, are necessary to resolve the nature of these subtidal plants as well as to investigate the relationship between genetic differentiation and overlapping morphology in plants at De Hoop.

This thesis is structured in the form of five main chapters, each written in the form of an independent paper and supported by a general conclusion and one previously published paper on the same general theme. The central theme is the dynamics, ecology and evolution of intraspecific and intraguild predation - specifically the determination of an interacting mechanism between the guild fish species Engraulis capensis and Sardinops ocellatus and its significance for future fisheries management.

Includes bibliographical references (leaves 210-273). / In South Africa, Ulva cultivation is of paramount importance to the marine aquaculture industry. Three local Ulva species (Ulva lactuca Linnaeus, Ulva rigida C. Agardh and Ulva capensis Areschoug) were selected for this research. The first two are currently cultivated on abalone farms for abalone feed and for use as bio-filters, and Ulva capensis was included because it is morphologically and biogeographically distinct from Ulva rigida in nature, despite the inability of molecular methods to separate them. Ulva rigida was collected at I & J farm and from nature at Kommetjie on the southwest of the Cape Peninsula, and U. lactuca was exclusively collected from I & J farm because it could not be found at sites where it had previously been recorded. Ulva capensis was exclusively collected from Kommetjie as this morphological species has not been recorded on abalone farms. The research also aimed to compare U. capensis with U. rigida on a variety of different measures, as molecular studies have suggested that they may represent a single polymorphic species.