Includes bibliographies. / Rocky islands in Saldanha Bay, southwestern Cape, South Africa, support aggregations of seabirds. Guano produced by the seabirds washed off the islands into intertidal and nearshore waters,where it provides a source of inorganic and organic nutrients. The concentrations of nutrients in intertidal rockpools at island and mainland sites in the Saldanha Bay area were measured,and the biological structures of intertidal communities at these sites were compared in the light of differences in intertidal nutrient status. Monthly measurements were made of algal production and of the growth, density, reproductive condition and mortality of the dominant intertidal herbivore, Patella granularis.The rate of intertidal algal production was enhanced on shores washed by nutrient-rich waters, and the growth rates and life-history patterns of populations of P. granularis were, in turn, modified by the increased availability of algal food. On unenriched shores rates of algal production and limpet growth and reproduction were slow. Seabirds thus influence trophic relationships between intertidal organisms, without themselves being components of the community. Islands in Saldanha Bay also support dense populations of African Black Oystercatchers Haematopus moqu.ini, which forage intertidally. Predation by oystercatchers on P. granular is resulted in a modification of limpet densities and population size structures, and a reduction in the intensity of grazing. The impact of predation was, however, modified by the presence, in intertidal waters, of nutrients from seabird guano, and the consequences thereof. It is proposed that differences in the structures of communities on rocky shores, and in the roles of processes influencing structure, might •be due, in part, to differences in the nutrient status of intertidal waters.

Includes bibliographies. / Blackwater lakelets in the south-western Cape are amongst the most darkly coloured humic waters in the world. In addition the aquatic invertebrate fauna of this region represents a relict and highly endemic group of the South Temperate Gondwanian fauna. The major environmental and biological variables were investigated over a period of fifteen months in six south-western Cape vleis (Suurdam, Gillidam, Sirkelsvlei, Grootrondevlei, Grootwitvlei and Rondevlei), which range in colour from a very dark brown to only slightly stained and vary in pH from 3.7 to 10.1. Using absorbance and fluorescence measurements and the Folin-Ciocallteu reagent, relative measures of the quantity and quality of humic compounds were obtained. Suurdam, Gillidam and Sirkelsvlei contained waters of greatest humic content (Suurdam mean A₂₉₀ = 6.561), with a common mid-winter to spring minimum; levels were lower in Grootrondevlei and Grootwitvlei (Grootrondevlei mean A₂₉₀ = 0.996), with a common mid-winter to spring maximum; and lowest in Rondevlei (mean A₂₉₀ = 0.284), with a slight peak in winter. Maxima were related to increased inflow of water with winter rain. Humic compounds in Suurdam, Gillidam and Grootrondevlei were of relatively high molecular weight and phenolic content, indicating an allochthonous origin. In Sirkelsvlei humic compounds were of lower molecular weight and phenolic content, possibly as a result of precipitation of the higher molecular weight fraction due to the high total salinity. Grootwitvlei and Rondevlei had lower molecular weight fractions probably as a result of autochthonous humic production, precipitation with calcium and greater rates of humic degradation; a higher molecular weight allochthonous fraction was present in winter in these two vleis. Buffering at low pH and the complexation of both iron and soluble reactive phosphorous were evident in Suurdam and Gillidam. Catchment geology, atmospheric precipitation, evaporation and the input of vertebrate excreta explain the inorganic chemical environments of the vleis. Acid, well-leached soils and calcareous sands resulted in mean pH values of 3.8 and 4.2 in Suurdam and Gillidam and 8.0 and 8.6 in Grootwitvlei and Rondevlei. The cation composition of the vleis on well-leached acid soils was primarily determined by the atmospheric precipitation of marine salt; evaporation and calcareous sands increased the salinity or relative calcium concentrations in some vleis. Animal excreta in Grootwitvlei and Rondevlei also alter the cation composition slightly, and increase the load of major nutrients. Nitrogen and phosphorous are largely of biological origin. Nutrient levels in the vleis are variously affected by marginal macrophytes, the sediments, primary production and the levels of humics. Chlorophyll a levels indicated low phytoplankton biomass in Suurdam, Gillidam and Grootrondevlei (Suurdam, mean chlorophyll a = 0.9ug1-¹ ) and no distinct seasonality; intermediate levels in Sirkelsvlei (mean chlorophyll a = 11.6ug1-¹ ) and high levels in Grootwitvlei and Rondevlei (Rondevlei, mean chlorophyll a = 60.4ug1-¹ ) displayed a common mid- to late-summer peak. Summer stratification was present only in Suurdam and Gillidam. Maximum phytoplankton biomass of the different vleis related to pH, the quantity and quality of the humic substances, and the nutrient loading. Chlorophyll b: chlorophyll a ratios and chlorophyll c: chlorophyll a ratios indicated a dominance of b- and c-containing species in Suurdam, Gillidam and Grootrondevlei and a dominance of species containing only chlorophyll a in Grootwitvlei and Rondevlei. Multi-dimensional scaling showed four distinct zooplankton community groupings. In Suurdam, the community was dominated by Microcyclops crassipes and was characterised by low zooplankton abundance (mean no.m-³ = 1783), a low species richness, an absence of limnetic cladocerans, and high species diversity (H') and evenness (J') indices. The community appeared to be limited by the low pH and the pH-dependent humic toxicity of the water. The communities in Gillidam, Grootrondevlei and Grootwitvlei were dominated by Metadiaptomus purcelli; otherwise that of Gillidam showed similar characteristics to that of Suurdam and was probably limited by the same factors. Both communities contained individuals of small mean size, more likely a result of limitation by the chemical environment rather than of predation pressure. A number of large-bodied limnetic cladoceran species and Lovenula simplex were present in Grootrondevlei, but absent from Grootwitvlei, possibly as a result of a visual predation pressure. In Sirkelsvlei the community was dominated by Metadiaptomus capensis and Lovenula simplex was present in lower numbers. Species richness, species diversity (H') and evenness (J') were low, with few limnetic cladoceran species present. High total salinity probably determines the community composition and seasonal variation. The eutrophic Rondevlei contains a community dominated by cosmopolitan and common Pan-Ethiopian species, in contrast to the endemic south temperate Gondwanian species of the other vleis. The community was dominated by Thermocyclops oblongatus, Brachionus calyciflorus and Brachionus rubens, and was characterized by greater species richness, and high species diversity (H') and evenness (J'). Total zooplankton abundances were much greater than in the other vleis (mean no.m-³ = 618944). Size-selective predation and the quantity and quality of the phytoplankton probably determine community composition. It is concluded that zooplankton diversity and abundance are influenced, both directly and indirectly, by the concentration and character of the humic substances and the pH, particularly at high concentration and low pH.

Bibliography: leaves 231-233. / One of the main purposes of this study was to determine whether general conclusions can be made about the association of insect herbivores with Berkheya and thistles and whether there are any 'rules' that have influenced the evolution of these associations. It is shown repeatedly that there are significant and interesting correlations between characteristics of the plants and their herbivore communities, but these are not universal.

Bibliography: leaves 169-198. / Observations and experiments on Jasus lalandii were undertaken over the period 1977 to 1986 to quantify the passage of carbon and nitrogen through populations at Oudekraal and Robben Island on the west coast of South Africa. The terms of the energy flow equation, C=P+R+G+UE+Ux+Uo+F (where C=consumption, P=production, R=respiration, G=reproduction, UE=Exuvial loss, Ux=excretion of exogenous nitrogen, Up =excretion of endogenous nitrogen and F=faeces), were quantified by combining field data and laboratory results. With this information the role played by J. lalandii in the kelp-bed ecosystem under the influence of the Benguela current was explored and quantified.

Includes bibliographies. / Typha capensis is indigenous to the Cape, but is thought to be threatening Cape Flats wetlands through invasion and encroachment. This thesis establishes the extent of such encroachment and investigates aspects of the phenology, life-history, growth, production and decomposition of the species in a Cape Flats wetland. The process of invasion by indigenous species rather than by alien species is discussed and the view that wetlands are threatened by mismanagement rather than by encroachment per se is examined. Finally, control methods particularly suited to local environmental and economic conditions are evaluated. T. capensis was shown to be typical of invasive plant species and is spreading in some wetlands. Encroachment is usually associated with the stabilisation of seasonal water-level fluctuations and under these conditions stands were spreading at 1.5m month. Demographic methods used to measure growth, production and decomposition made it possible to quantify leaf fragmentation and shoot collapse, processes that are generally ignored during decomposition studies. Results showed that the structure of Typha stands is related to flood regime, and that flood regime has an important effect on production, litter formation and decomposition.

Bibliography: leaves 186-205. / A seasonal study of the nonbreeding foraging ecology of Grey Plovers and Whimbrels was undertaken at the Zwartkops estuary, South Africa, and additional data were collected from a variety of sites in tropical and south temperate latitudes during the premigratory period. The main objective of the study was to provide comparative data on shorebird foraging ecology in the southern hemisphere, in order to contribute to the general understanding of shorebird foraging behaviour and migration patterns.

Includes bibliographical references. / A biogeographic analysis was undertaken using data for intertidal rocky-shore communities obtained from quantitative biological surveys made around the southern African coast. Substantial differences in species composition, abundance and trophic structure were found between 15 different rocky shores along ca. 5000 km of coast. These differences allowed the division of South African coast into three major biogeographic provinces. The large-scale variations were due to geographical differences in the physical environment including temperature, nutrients and primary production. Large-scale and local-scale vertical and horizontal zonation of intertidal communities were investigated. Local-scale variations were largely due to the effect of differential wave action, but also included the vertical gradient of desiccation. Gradients of wave action generate divergence of the mid-to-low zone communities, whereas in the upper shore communities converge due to the desiccation gradient. The consistent repetition of the vertical and horizontal patterns of patterns of distribution for both community biomass and species richness lead to the conclusion that the physical processes involved in the creation of local patterns also operate over a large geographical scale. The patterns of community structure on southern African rocky shores are investigated in relation to in-situ primary production and micronutrient concentrations. A conspicuous gradient of intertidal primary production was found.

Includes bibliographies. / Gastropods of the genus Burnupena are very common rocky-shore whelks endemic to the Southern African region. However, despite recent revisions of the genus, difficulties in identification persist, due mainly to the occurrence of phenotypic intermediates between sympatric species. Samples of Burnupena were collected from 17 sites along the coast of South Africa. Variation in shell morphology was examined using multivariate analyses. The results revealed that the degree of variation within species is very high, and that shell form and colour can be influenced by local environmental conditions. Nevertheless, most populations of the individual species clustered together. Morphological differences between species were small, although distinctions could be discerned, with not all species being confused with all other species. However, on the basis of morphology, there will always be a few individuals which will remain difficult to identify. Examination of the radulae from all of the species of Burnupena using both light and electron microscopy showed that the radula is of little or no practical value in distinguishing between species. Whilst some differences could be detected in some characters, these were not consistent, either within or between species. However, the radula is diagnostic at the generic level. The populations of Burnupena were analysed for allozyme variation at 25 loci. Variation within species was high, and in all of the species, significant population differentiation was obseNed. A significant correlation between genetic and geographic distance was found. Nei's genetic distances within species were low (means per species ranging from 0.01 to 0.05), and the populations of each species clustered together. Unlike their morphological differences, the species were mostly well differentiated genetically, with Nei's distances between species ranging from 0.1 to 1.45. Compared to the other species, B. cincta and B. lagenaria were relatively little differentiated from each other. B. catarrhacta was strongly differentiated from all of the other species. Comparisons between sympatric populations suggested complete reproductive isolation between the species.

Includes bibliographical references (leaves 163-180). / In multispecies fisheries knowledge, personnel and funding limitations often create the dilemma over which species should be the first to receive management and research attention. This thesis uses a Multi-Criteria Decision Analysis approach to prioritize 176 South African linefish species on the basis of a number of criteria indicating conservation and socio-economic importance. Each species importance was assessed from the points of view of (1) conservation, (2) each fishery sector separately and combined and (3) the overall combined conservation and sectorial importance. Relative scores within each of the fishery sectors were dominated by two or three species such that the scores separating the remaining species from each other were small. On the whole, the top species included those most important in each sector, biogeographic region and in terms of conservation. The separate and overall ran kings should assist in the development of broadly acceptable management strategies for different fish. Catch data for 129 of 255 functional estuaries on the South African coastline were reviewed and the relationships between fish catch and estuarine size, type and biogeographical region analysed using simple and multivariate models. Estuary size alone explained over 80% of the variation in catch in the warm temperate region and over 90% of the variation in catch in the cool temperate and subtropical region. Further analysis of the two main estuarine types (permanently open and temporarily open/closed estuaries) revealed higher productivity for the permanently open systems. Both estuarine size (ha) and type (5 types) were used to explain catches using general linear models. The models were able to explain 82-98% of the variance in catches. The total estuarine catch in South Africa was estimated at 2 480 tons per annum with a total value of R748 million, of which 99% could be attributed to recreational angling. Estuarine contribution to the inshore marine fisheries was estimated at approximately R846 million per year with estuarine dependent species comprising 83% of the catch of the recreational shore and commercial seine and gillnet fisheries and only 7% of the catch of the recreational spearfishery and commercial and recreational boat fisheries. Total value of estuarine and estuary-dependent fisheries was estimated to be R1.594 billion per annum in 2008 rands. The cool-temperate Olifants and warm temperate Breede estuaries on the west and south coasts of South Africa have both seen a >35% reduction in mean annual runoff (MAR) from a historical reference condition to the present day with a >60% reduction possible under future development. With almost no exceptions, the Olifants Estuary fish assemblage has seen an overall 20% decrease in abundance from reference to the present day and will gradually decline to 55% of reference with a predicted future 60% reduction in MAR. Consequently, future reductions in flow are likely to see the Olifants Estuary progressing towards a low biomass, low diversity, marine-dominated system. In contrast, with the exception of some key exploited species, fish abundance in the Breede Estuary has increased by 6% from reference to the present day and is likely to increase to 115% of reference with future reductions in flow. In all, the fish assemblage will experience a gradual change from a relatively high-diversity low-abundance freshwater-rich system under historical flow conditions to a high-diversity, highabundance, marine-dominated system with future reductions in flow.

Includes bibliographical references. / Combing results from phylogenetic and population level studies suggests that climatic cycling has had a profound influence on montane bird speciation in Africa. The results from this thesis suggest that there is deep genetic divergence between many clades (8-12%) of montane passerine birds in Africa, with some shallow divergence towards the tips (4-6%). For widespread species reciprocal monophyly has not been reached in some instances, but generally there is some support for the refuge idea that isolation (fragmentation) of montane forests has facilitated speciation. However, most speciation events happened well before the Pleistocene and therefore the Pleistocene Refugia Hypothesis is not appropriate as a model with which to explain patterns of montane bird diversification in Africa. Rather, both dispersal and vicariance have played important roles in shaping montane bird communities. Thus, a refugia type model does work, but only within the context of pulsed or cyclic expansion and contraction of montane forests, supported in thus study by the consistent recovery of spatially structured areas of endemism, despite varying temporal dynamics.