Bibliography: leaves 138-156. / The black mussel Choromytilus meridionalis (Krauss) forms an important link in the food chain of the South African west coast kelp beds, transferring energy from macrophyte debris, phytoplankton and bacteria to major predators such as the rock-lobster Jasus lalandii. Although a large body of work has been carried out on the physiology, energetics and population dynamics of the black mussel, no attempt has been made to link the actual food available in the field, with the animal's digestive capabilities. This work examines the carbon and nitrogen resources available from kelp debris, phytoplankton and bacteria, and quantifies the animal's ability to utilise these resources according to its needs.

Bibliography: leaves 195-213. / This thesis focused on two aspects of predation by the West Coast rock lobster (Jasus lalandii). These were (1) the problem of slow growth currently observed in adult male rock lobsters and the putative link between growth rate and food availability, and (2) the influence of rock-lobster predation on the benthos, but more specifically on sea urchins and juvenile abalone.

Bibliography: p. 231-256. / The primary objectives of this study were to assess the protected status of birds in the Succulent and Nama-Karoo, and to identify areas, using a GIS approach, where new protected areas could be established. The Karoo sensu lato lacks a distinctive avifauna, but is rich in species. A total of 407 bird species has been recorded in the Succulent and Nama-Karoo, of which 294 species are considered typical of the region. The Karoo is not particularly rich in bird species endemic to the region, and all Karoo endemic species occur in both biomes. The Nama-Karoo has an unusually high species richness of nomadic birds, and both the Succulent and Nama-Karoo have an unusually high species richness of larks (Alaudidae) compared with other biomes. The Succulent and Nama-Karoo have stochastically low annual rainfall and generally low above-ground primary production. Rainfall is often highly localized and varies annually in amount and timing. The variability of the rainfall and long dry spells or severe droughts create a mosaic so that high and low resource areas occur as patches in the landscape. Resident species of birds tend to maintain low densities and wait for rainfall events, whereas nomadic species search for high resource patches scattered in time and space, so that their respective densities likewise vary temporally and spatially. Compared with other biomes in southern Africa, there is a high species richness of nomadic birds in the Karoo. The small nomadic larks are most common in areas of perennial and annual desert grasses, and they feed on grass seeds, whereas resident granivorous birds tend to feed on the seeds of forbs and shrubs. Clutch sizes of the nomadic larks birds are small, apparently selected for by the need for a short breeding cycle.

Bibliography: 172-183. / Field surveys were carried out in the kelp beds of the shallow subtidal off the south western Cape of South Africa, which confirmed the existence of a strong positive relationship between the urchins Parechinus angulosus and juveniles of the abalone Haliotis midae. Both species occupied primarily hard substrates, showing preferences for encrusting corallines. Of the juvenile abalone sampled, > 98% were found beneath sea urchins. All small (3-10 mm shell length) and medium sized (11-20 mm shell length) abalone juveniles occurred under urchins, whether on flat or vertical reef, or in crevices. A small proportion (approximately 10%) of large juveniles (21-35 mm shell length) were not found under urchins, and in these instances all occupied crevices instead. Subsequent surveys also revealed a positive, but weaker, association between abalone recruits (<3 mm shell length) and urchins - an unexpected result, given that abalone recruits are cryptic against the encrusting coralline substrate that they occupy preferentially. Thus camouflaged, they were assumed to gain little additional benefit from sheltering beneath urchins. Selectivity indices showed that, amongst different morphological categories of encrusting corallines, recruits showed preferences for strongly-textured corallines, such as the so-called "knobbly" and "paint" textures. Lower densities of recruits per unit substrate area were recorded on the smoother "velvet" corallines. However, almost all (80%) of recruits were found on velvet corallines occurred under urchins, as opposed to 28 and % of recruits on paint and knobbly corallines respectively.

Bibliography: leaves 78-90. / Laboratory studies were conducted on juvenile horse mackerel to examine feeding selectivity and rates of zooplankton consumption of two size classes of fish. Fish were fed a variety of natural zooplankton assemblages and sequential subsampling of water in the experimental tanks provided estimates of prey concentration. Video observations were used to examine feeding behaviour and to investigate the feeding response of horse mackerel to various food types and prey sizes.

Until recently, marine bioinvasions have received little attention in South Africa, and the status of intertidal marine aliens was last assessed in 1990. I thus investigated the present distribution and status of three intertidal alien species (Mytilus galloprovineialis, Care in us maenas and Careinus aestuarii) and documented the presence and status of a previously unknown invasive, the Japanese oyster, Crassostrea gigas. M galloprovincialis was recorded along the entire west coast of South Africa, with populations extending up to central Namibia, and along the south coast of South Africa to 40 km west of East London. Along South African shores a total stock of 35 403.7 tons (± 7 241.4 SE) was recorded, with the vast majority of the stock occurring on the west coast (31 054.5 tons ± 6 274.1 SE). C. maenas supports a substantial population of 133 568 individuals (95 % confidence range == 97 694 - 166 862) in Table Bay Harbour which appears to be acting as in invasion incubator for surrounding areas. A new population of 9 180 individuals (95 % confidence range 5 870 - 12 003) was recorded in Hout Bay Harbour. This represents a range extension along the Cape Peninsula. The low intertidal abundance of this crab between these localities is thought to reflect the inability of C. maenas to inhabit exposed habitats. C. aestuarii was not recorded during this study despite previous documentation of its presence. In 2003, naturalised populations of C. gigas were documented in the low shore zone of the Breede, Goukou and Knysna Estuaries, but not on the open coast. This may again be indicative of the limiting effect of wave action on species alien to South African shores. As such, the presently undetermined impact of this species may well be focused on estuarine habitats. To quantify the threat posed to intertidal communities by M galloprovincialis, changes in community structure on the rocky shore of Marcus Island and the sandy shore of Langebaan Lagoon were measured. In both habitats, the invasion significantly altered community composition. On Marcus Island the effects were focused within the mid-to-low intertidal zones, where habitat complexity was enhanced and patchiness was decreased, resulting in dramatic changes in invertebrate density, species number, richness and diversity. On sandy shores, M galloprovincialis beds changed available habitat structure, resulting in a concurrent invasion by indigenous rocky shore species. In the sediment below the mussel beds, soft-sediment species were excluded due to anoxia. Following a die-off of the mussel beds the rocky shore species disappeared, but were not replaced by sandy shore organisms as the sediment remained uninhabitable. The subsequent removal of the dead mussel shells appears to have recovered, but community composition is still to return to the preinvasion state. In order to consider the biological viability of a fishery for A1. galloprovincialis in the Northern Cape, a harvesting project operated by two impoverished coastal communities was initiated. Harvesting took place on a rotational basis and twelve sites, nested within four harvesting locations, were each exposed to spectrum of harvesting intensities (F=O, F=30%, F=60% and F=90%). A dynamic biomass-based fisheries model predicted monthly Maximum sustainable yield (MSY) estimates of 1 560 kg per 100 m of shore in March-April and September-October, but two orders of magnitude less (15 kg) during the remaining months. These peaks correspond to spawning periods of this mussel along the South African west coast. Experimental manipulations revealed high recruit densities recorded at low harvesting intensities (2 000 20 000 per 0.01 m exceeding levels required for population maintenance. However, if adult mussel beds are eliminated or significantly reduced (which occurred at F=30% or above), recruitment may limit stock replenishment. Indirect effects on non-target species were also considered. Intertidal communities changed dramatically in response to harvesting, with increased algal dominance and shifts in the distribution of grazers between primary- and secondary-substrates. Community composition did not return to the pre-harvest state after four months of no harvesting, even in areas which were only harvested at an intensity of F=30%. Northern Cape intertidal communities are thus considered to have low resilience and elasticity in response to harvesting of A1. galloprovincialis. It is thus recommended that a harvesting intensity of between 10% and 30% be employed if A1. galloprovincialis stocks in the Northern Cape are to be harvested on a commercial basis. This would protect stock replenishment and minimise effects on intertidal communities. In addition, harvesting should be focused within the two spawning seasons spanning peak MSY estimates so as to maximise yield and aid community recovery between harvests. If implemented, this would represent the first instance in South Africa of a marine invasive species being utilised in a way that employs dynamic fisheries management to achieve socioeconomic goals, while taking into account the effects on other elements of the biotic community.

Includes bibliographical references. / Temperature is an important environmental variable for aquatic invertebrates as it affects their development, reproduction and survival. Temperature also affects the abundance and distribution of individuals in a stream or river. Stream temperatures are affected by human impacts which include not only impacts such as pollution, abstraction of water and the removal of riparian vegetation, but also the affects of climate change. In the Western Cape Province, South Africa, it is predicted that air temperatures will increase and winter rainfall will decrease. This in turn will affect water availability and water temperatures in streams and rivers. Thermally sensitive species are threatened by increases in water temperature, but currently very little information exists on the thermal tolerances of aquatic invertebrates in South Africa. In order to rectify this problem baseline data on thermal tolerances of aquatic species needs to be collected, together with stream temperature and associated invertebrate community data. An attempt was made to collect some of these much needed data in the Western Cape Province. Two methods, namely Critical Thermal Maxima (CTM) and LT₅₀ experiments, were used to determine the thermal tolerances for a range of aquatic insect nymph species from the southwest fynbos bioregion and the south coast fynbos bioregion. The results from the experiments provided information on the relative thermal sensitivities of the species. Overall Aphanicerca capensis (form C and undescribed form), Notonemouridae ranked as the most thermally sensitive for both experiments. The A. capensis species complex (and possible other notonemourid stoneflies) may potentially be used as an indicator of changing stream temperatures in the Western Cape Province. To rapidly determine thermal sensitivities the CTM experiments are recommended rather than the more time consuming LT₅₀ experiments as the relative thermal tolerance for the species tested ranked the same for both experiments. It is suggested that LT₅₀ experiments of longer duration be investigated in order to compare the experiments to naturally-occurring thermal stress. Stream temperature and community composition data were collected from Window Gorge Stream, on Table Mountain, to provide baseline data for future monitoring and understanding of potential changes in thermal profiles. Temperature loggers were placed at six sites along the stream. Stream temperatures were fairly low but the stream ran dry during the late summer months (February through to April/May). From the community composition data collected the highest diversity was found during the winter months, as expected. The community composition did change down the length of the stream, with the species composition found near the source being quite different to that of the species composition found lower down the mountain. Temperature and associated oxygen saturation were two important variables related to the community composition down the length of the stream. It is important that experimental data be combined with field data, enabling field sampling to focus on the collection of information on the abundance of the thermally sensitive species (e.g. A. capensis species complex). Recorded stream temperatures also provide reference conditions for the species tested in the laboratory. Climate change is likely to have an affect not only on stream temperatures but also on water availability, which will both influence stream communities and ecosystems and it is important to understand what these potential effects might be.

Bibliography: p. 237-249. / This study investigates the population genetics and behavioural ecology of the Greywing Francolin, Francolinus africanus, and identifies factors which influence the distribution and abundance of this important gamebird. It also develops scientifically sound management strategies which should allow the maintenance of populations at levels which will produce sustained and economically viable hunting yields as a co-product of agriculture. Examination of genetic variability based on allozymes disclosed estimates of average within-population heterozygosity higher than that for most birds, and for all other galliformes for which data are available. Thus, Greywing apparently have a high degree of population stability and large effective population sizes. Indirect estimates of migration and several significant allelefrequency differences between nearby coveys suggest that there is a greater degree of genetic subdivision among Greywing populations than among populations of other birds. However, although the data suggest that populations are genetically differentiated on a large geographical scale, they also indicate that there is considerable dispersal, which produces outbred subpopulations on a fine geographical scale. Greywing therefore have a wealth of genetic variability that may 'buffer' populations against environmental changes, responsible hunting and/or short-term demographic bottlenecks. They also appear to undergo sufficient migration so that recruitment from adjacent populations will ensure population stability in hunted areas.

Includes bibliographical references. / The field metabolic rate (FMR) and water flux of the herbivorous Namib sand-dune lizard, Angolosaurus skoogi, was measured during the summer non-breeding period (early January) by means of doubly labelled water. FMR was about half that expected for a lizard of this size. Water flux and laboratory measured standard metabolic rates were, however, typical of other desert lizards. It thus appeared a priori that this species was behaviourally reducing metabolic costs through reduced activity. This generated questions with regard to the ecological and physiological significance of low FMRs. Is the reduction forced by intolerable environmental conditions or the need to stay in positive water and energy balance? Alternatively, is activity reduction voluntary and geared towards optimizing growth and storage, possibly in preparation for periods of physiological stress ? The research required to answer these questions forms the basis of this thesis. There has been much discussion about the evolutionary and ecological significance of growth rates. The consensus seems to be that, under most circumstances, animals are adapted in ways that maximize growth or optimize growth in relation to realistically attainable rates of gross energy intake. Animal behaviour may be influenced by factors unrelated to growth considerations such as starvation, involuntary hypo/hyperthermia, predator evasion and social interactions. These factors may be difficult to identify and isolate, making this hypothesis difficult to test. Previous studies on the biology of A. skoogi have shown that this species has a perennially available food source, a wide range of potential body temperatures at its disposal and a low predation risk. Social interaction appear to be confined to the breeding season. This species is thus a particularly suitable subject for a scope for growth optimization study.

Bibliography: leaves 73-91. / Abalone exposed to air incurred greater metabolic and structural stress in muscle than do abalone at rest. Since foot and shell adductor muscle texture and flavor affect economic values of H Midae, the investigation sought evidence of differences attributable to transport of the commercial South African abalone based on environmental and exercise inducement. Tauropine dehydrogenase from Haliotis. midae muscle exhibits its highest activity 53.85 X 13.56 U g-1 wet weight in shell adductor muscle. The activities of octopine dehyedrogenase, strombine dehydrogenase or alanopine dehydrogenase in adductor muscle were very low. Therefore, tauropine dehydrogenase was isolated from adductor muscles for enzymatic determination oftauropine. Tauropine dehydrogenase was purified 8.5-fold with 47% recovery.