West Coast Of Southern Africa Research Articles

Diet and condition of juvenile deep-water hake Merluccius paradoxus on the west coast of southern Africa

The composition of the diet of juvenile deep-water hake Merluccius paradoxus is described and compared for three body-condition groups (below-average, average, and above-average). Diet was analysed using three metrics: occurrence, numeric and gravimetric. Juvenile hakes were caught in January and February of 2012 by means of 28 trawl deployments from the RV Dr Fridtjof Nansen between Orange Banks and Hondeklip Bay on the west coast of southern Africa at depths of 30-232 m. The 300 individuals analysed were a representative sample of all juveniles caught (3 114 fish), ranging in length from 52 to 205 mm (average length 107 mm). Their diet consisted of the euphausiid Euphausia lucens, the hyperiid amphipod Themisto gaudichaudii, the stomatopod Pterygosquilla armata capensis, and mesopelagic fishes Maurolicus muelleri and Lampanyctodes hectoris. The only significant difference in diet between the body-condition groups was for euphausiids and hyperiid amphipods in the numeric metric. A new method of assessing fish condition using otolith weight was tested. Because of the large variability in the data and small sample size, this method could not be applied effectively in this study. However, otolith weight has potential as a new fish condition metric when the variability can be lowered.

A targeted drilling and dating campaign to identify Stone Age archaeological sites before excavation in west coast southern Africa

Here we present the results of a targeted drilling campaign that facilitated a geochronological study with coarse sampling resolution inside a new cave site, Simons Cave, on the west coast of southern Africa. A combination of radiocarbon ( 14 C) dating and optically stimulated luminescence (OSL) dating was used as a range-finder. Results confirmed preservation of Holocene and late Pleistocene sediments up to 133 ± 35 ka, overlapping with the ages of Middle Stone Age (MSA) occupations of the broader west coast region. A subsequent, systematic test-excavation at the site then embarked on a second geochronological study with a higher sampling resolution. Ultimately, the comparative study confirmed the potential of Simons Cave as a new site for the exploration of hominin occupation through the later Pleistocene and Holocene, yet raised several issues concerning the direct comparability of information deriving from drilled sediment cores and actual archaeological excavation.

Satellite Sea Surface Temperature Product Comparison for the Southern African Marine Region

Several satellite-derived Sea Surface Temperature (SST) products were compared to determine their potential for research and monitoring applications around the southern African marine region. This study provides the first detailed comparison for the region, demonstrating good overall agreement (variance < 0.4 °C2) between merged SST products for most of the South African marine region. However, strong disagreement in absolute SST values (variance of 0.4–1.2 °C2 and differences of up to 6 °C) was observed at well-known oceanographic features characterized by complex temperature structures and strong SST gradients. Strong seasonal bias in the discrepancy between SST was observed and shown to follow seasonal increases in cloud cover or local oceanographic dynamics. Disagreement across the L4 products showed little dependence on their spatial resolutions. The periods of disagreement were characterized by large deviations among all products, which resulted mainly from the lack of input observations and reliance on interpolation schemes. This study demonstrates that additional methods such as the ingestion of additional in situ observations or daytime satellite acquisitions, especially along the west coast of southern Africa, might be required in regions of strong SST gradient, to improve their representations in merged SST products. The use of ensemble means may be more appropriate when conducting research and monitoring in these regions of high SST variance.

Aerosol optical properties and direct radiative effect over Gobabeb, Namibia

Atmospheric aerosols contribute significantly to the uncertainty in radiative forcing effects that influence the climate and pose a significant health risk to humans. The climatic implications of aerosols are dependent on many variables, including aerosol size, shape, chemical composition, and position in the atmospheric column. The radiative impact of aerosols transported over the west coast of southern Africa has been found, in particular, to be complicated by the aforementioned aerosol properties. This study investigated the columnar optical properties of aerosols over Gobabeb, Namibia (23.56oS, 15.04oE, 400 m asl) using sunphotometer data between December 2014 and November 2015. Aerosol mean optical depth AOD500 had its maximum and minimum values in 2015 August (0.37±0.30) and June (0.06±0.02), respectively. The Angström parameter was mostly above unity during the study period and indicated the prevalence of fine particles for the most part of the year with maximum and minimum values observed in August 2015 (1.44±0.19) and December 2014 (0.57±0.19), respectively. The columnar water vapor was highest in January (2.62±0.79) and lowest in June (0.76±0.27). The volume size distribution showed the fine particles having a mean radius of about 0.16 μm and the coarse mode had variation in sizes with a radius ranging between 3 μm and 7 μm. The single scattering albedo at visible wavelengths ranged between 0.87 and 0.88. The phase function was high at small angles but minimum at about 140o in all seasons. The radiative forcing showed a heating effect in all seasons with maximum and minimum in winter (9.41 Wm-2) and autumn (3.64 Wm-2), respectively. Intercomparison of the sunphotometer data with the Moderate Resolution Imaging Spectroradiometer (MODIS) showed that the satellite sensor overestimates the aerosol loading compared to the ground-based sunphotometer measurements. Both sets of observations were better correlated during the spring and winter seasons than for summer and autumn.

Patterns of geographic variation between mitochondrial and nuclear markers in Heaviside's (Benguela) dolphins (Cephalorhynchus heavisidii).

The Heaviside's (or Benguela) dolphin (Cephalorhynchus heavisidii) is endemic to the west coast of southern Africa. The present study investigated the population genetic structure across a large portion of the species distribution using mitochondrial control region and nuclear (microsatellite) markers. A total of 395 biopsy skin samples were analyzed; they were collected from free-ranging Heaviside's dolphins in 7 locations along 1650 km of coast between Table Bay, South Africa and Walvis Bay, Namibia. Both genetic markers rejected the hypothesis of 1 homogenous population but revealed contrasting results in the genetic structuring of putative populations. Mitochondrial DNA suggested either 2 populations or a fine-scale division with 6 (sub) populations, while microsatellite markers were indicative of 2 widespread populations with measurable gene flow between them. Neutrality tests and mismatch distribution of the mitochondrial sequences indicated a departure from mutation-drift equilibrium due to a population expansion at the 2 extremes of the geographic range, but not towards the middle of the distribution. These results highlight the importance of evaluating multiple genetic markers to gain reliable insights into population processes and structure.

Geochemistry of Al and Fe in freshwater and coastal water colloids from the west coast of Southern Africa

Suspended iron-rich colloids play an important role in nutrient and contaminant transport in fluvial systems, and may ultimately provide an important source of Fe which is required for marine biological productivity. Despite being fundamental to Fe colloid behaviour in biogeochemical systems, the physical and chemical characteristics of these colloids are poorly constrained, especially at the molecular level. Here we combine traditional chemical extraction techniques with X-ray Absorption Near-edge Structure (XANES) spectroscopy to investigate and compare the bulk and molecular-level speciation of Fe and Al in suspended colloids from fluvial (Berg, Olifants and Orange Rivers) and marine sampling sites on the western margin of Southern Africa. The bulk extraction methodology shows a variable distribution of Fe among five different operationally-defined Fe pools, yet our spectroscopy results reveal that the majority of particles in the 10 nm–4 µm size fraction do not match crystalline or residual Fe spectral signatures and are thus likely to be poorly-crystalline. Aluminium K-edge XANES reveals that the Al coordination environment in aquatic colloids is diverse (e.g., relative to oxo ligands, the number of coordinated OH− ligands ranges between 0 and 6), and that the smallest sized colloids are always highly hydroxylated (i.e., their coordination environment is similar to Al in Al(OH)3 or 1:1 clays). The Al XANES further reveals a common association between Al and Fe-rich colloids, where the average measured Al/Fe ratio is 0.10 (±0.09) among all the particles measured in this study. The Al that co-occurs with Fe preferentially has a coordination environment similar to Al in 1:1 clays (i.e., two oxo ligands and four hydroxyl ligands), either further implying the amorphous nature of the Fe colloids or reflecting Al as surface complexes or as inclusions of nano-sized Al clusters. The observed high degree of disorder and the presence of Al association/substitution in iron-rich colloids observed in the Southern African systems will strongly influence the biogeochemical behaviour of these colloids (e.g., surface sorption capacity, solubility and dissolution rates). These findings contribute greatly to our understanding of natural Fe colloid and nanoparticle speciation and are anticipated to have global relevance to other aquatic systems in which ‘reactive’ or ‘poorly crystalline’ classes of suspended particulate Fe have been identified.

Geographical variation in morphology of the two dominant kelp species, Ecklonia maxima and Laminaria pallida (Phaeophyceae, Laminariales), on the west coast of Southern Africa

Laminaria pallida and Ecklonia maxima are large, commercially valuable kelps that co-dominate inshore waters of the west coast of Southern Africa in a geographically changing pattern. In the south, E. maxima dominates and forms a canopy in shallow waters (< about 5 m deep), with L. pallida forming a sub-canopy and extending down to 20 m or more. Northward along the Southern African coast and into Namibia, E. maxima is progressively replaced by L. pallida. Corresponding with this change in dominance, L. pallida shows certain morphological changes along the south-to-north geographical gradient. To explain these phenomena, we examined a range of morphological characters in both kelps (stipe length, stipe weight, stipe outer diameter, stipe inner diameter, length of hollow section in the stipe, and frond weight), and various environmental factors (seawater temperature, seawater turbidity, cloud/fog data, daylength, and wave and wind data). Our results, based on measurements at seven sites along 1600 km of coast between Cape Town and Swakopmund (Namibia), quantified and confirmed the change in dominance and the northward increase in stipe hollowness in L. pallida. The morphology of E. maxima did not change with latitude. Water turbidity, wind speed, and wave height differed significantly along the coast. However, only turbidity showed a steady trend, increasing northward in terms of all indicators (chlorophyll a, particulate inorganic carbon, particulate organic carbon) while wind speed and wave height showed a generally decreasing trend. Furthermore, the hollowness of L. pallida was also not related to the flexibility of the stipes. Our results suggest that L. pallida sporophytes may progressively outcompete E. maxima northward, perhaps because they are more low-light tolerant, and we suggest that by developing a hollow stipe, the sporophytes may grow faster in length, potentially increasing their competitive advantage in the shallow water where they must compete with sporophytes of E. maxima.

Implications of summer breeding frogs from Langebaanweg, South Africa: Regional climate evolution at 5.1 mya

&#x0D; &#x0D; &#x0D; No direct palaeoclimatic proxies have been available to indicate the seasonality or amount of rainfall on the west coast of southern Africa during the Early Pliocene. The Benguela Upwelling System (BUS) is today one of the factors responsible for the present-day aridity on the west coast of southern Africa. The initiation of the BUS is frequently linked to the entrenchment of aridity and the establishment of the current winter rainfall pattern on the west coast; however, marine proxies are inconclusive regarding the effects of past fluctuations in the BUS and sea surface temperatures on the rainfall regime. Neither the fossil evidence nor the fact that plants using the C3 photosynthetic pathway predominate at this time, provide direct evidence of winter rainfall at Langebaanweg. We challenge certain assumptions which are commonly made in the literature regarding the timing of inception of a winter rainfall regime on the west coast and the onset of aridity in the Langebaan region, and provide new evidence as to seasonality of rainfall at Langebaanweg in the Early Pliocene. Herein, the identification of frog species from the genus Ptychadena from Langebaanweg provides new and compelling evidence for a summer rainfall regime, or of at least significant summer rainfall, at 5.1 mya in the southwestern Cape of South Africa.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; Significance: &#x0D; &#x0D; &#x0D; &#x0D; Advances understanding of the evolution of the winter rainfall zone on the west coast of South Africa&#x0D; Assesses evidence for the inception of aridity and a winter rainfall regime on the west coast of South Africa&#x0D; Fossil Ptychadenidae from the Early Pliocene site of Langebaanweg provide evidence for a summer rainfall regime at 5.1 mya on the west coast of the southwestern Cape.&#x0D; &#x0D; &#x0D; &#x0D;

Variation in physical and mechanical properties from three drought tolerant Eucalyptus species grown on the dry west coast of Southern Africa

Southern Africa, and specifically its western parts is dominated by low rainfall areas, and it is expected that the rainfall in most of these parts will in future decrease further due to climate change. Woodlots of fast-growing, non-invasive tree species can provide the opportunity to produce wood and release the pressure on natural woodlands, while creating much needed income to inhabitants. Over the last two decades several trials of Eucalyptus species that could potentially withstand arid conditions were established on the South African west coast. The three most promising genotypes according to their volume growth were selected among 46 pure and hybrid species from two 20-year-old trials for further evaluation. These included 10 Eucalyptus grandis × Eucalyptus camaldulensis hybrid trees, 9 Eucalyptus gomphocephala trees, and 9 Eucalyptus cladocalyx trees for a total of 28 trees. The objective of the study reported here was to investigate the within-tree and between species variability of selected physical and processing properties determining the suitability of these three species for lumber production. The density, microfibril angle, spiral grain angle, MOE, MOR, radial and tangential shrinkage, twist, bow, splitting, and collapse were measured in a radial and longitudinal gradient. Valuable insights were gained which could provide decision support for planting, processing and further research on these species when grown in arid conditions. The E. grandis × camaldulensis hybrid was inferior in terms of most relevant properties to the other two species evaluated. The main shortcoming of both E. gomphocephala and E. cladocalyx was the high levels of twist in lumber.

Optimistic Suburbia, building an heritage

Between the 1960s and 1980s Luanda, Lisbon and Macao saw the emergence of a number of residential complexes that had a shared matrix: privately developed high-rise buildings aimed at the middle-classes and located on the periphery. The three cities had different urban histories, even if they were united by the common denominator of being under Portuguese political and administrative control. Lisbon was a European capital made up of successive strata and occupation phases with ancient and mediaeval predecessors. Luanda was an old outpost on the west coast of Southern Africa that gradually took on the status of main city in Angola in the course of the 19th century and, in 1960, was in an ongoing process of rapid population growth and was expanding through its many areas of informal occupation. And Macao, an Asian city within the confines of a peninsula and the boundaries that separated it from continental China, was in a process of self-renewal and permanent reutilization of the space, with the urban transformation processes being characterized by a speed that set it apart from the conventional European city. It is in this context of diversity of backgrounds and conditions that an analysis of these residential complexes takes on particular importance, by applying residential models with a common urban, architectural and social matrix. This article stems for a wider research project entitled “Homes for the biggest number: Lisbon, Luanda, Macao” and its main intent is to analyze the residential models that were applied in the construction of the peripheries of cities with a Portuguese background from the 1960s onwards, and its current state in an historical and patrimonial perspectives.

Bald kelp: natural and harvesting-induced frond loss in the South African kelp Ecklonia maxima

Ecklonia maxima dominates kelp beds on the west coast of southern Africa, and is commercially and ecologically valuable. Some plants lose all their secondary blades (fronds), leaving only the gas-filled bulb and short primary blade at the top of the stipe. These ‘bald’ kelps may persist for months or longer, occupying substratum space but contributing little to productivity. We investigated natural causes of balding in five kelp beds in False Bay, South Africa, and the effect of simulated commercial frond-harvesting on loss of fronds. Densities of sporophytes with and without fronds were measured at the water surface during low tides. Generalised linear modelling analysis showed a significant relationship between balding and site (whether sheltered from or exposed to swell/wind), position in the kelp bed (shoreward or seaward) and total E. maxima density. We conclude that balding is caused mainly by drying of meristematic basal regions of fronds during emersion of kelp heads at low tide. After partial harvesting of fronds, kelp heads floated higher out of the water, but after 95 days frond loss was significantly higher only when fronds were cut too close to the primary blade, possibly because of damage to meristematic tissue. Nevertheless, increased emersion that results from frond-harvesting may increase desiccation and blade loss and we suggest caution in setting harvest limits for this kelp.

Geology of the Cenozoic Namakwa Sands Heavy Mineral Deposit, West Coast of South Africa: A World-Class Resource of Titanium and Zircon

Exploration for heavy minerals along the coastal strip of southwest Africa led to the discovery and subsequent delineation of the Namakwa Sands deposit near Brand-se-baai in 1987. Currently, Tronox Limited controls the Namakwa Sands operation, which has developed into a significant, global producer of titanium slag, pig iron, ceramics quality zircon and rutile concentrates. The Namakwa Sands deposit is classified as a megaresource with 1.17 billion tons (Bt) of in situ ore, containing an estimated 92.6 million metric tons (Mt) of total heavy minerals and the equivalent of 23.9 Mt TiO2 units and 9.4 Mt zircon. The siliciclastic, arenaceous deposit is divided into two adjacent orebodies, referred to as Graauwduinen West and Graauwduinen East. The Graauwduinen West orebody consists of three strandline-dune couplets set in a transitional shallow marine-aeolian environment, whereas the Graauwduinen East orebody comprises a largely unrelated dune deposit. Superimposed onto the ore-bearing sequence is a pseudostratigraphy of duricrust that effectively cemented the bulk of the mineralized sands to various degrees of hardness. The two orebodies are profoundly different in many aspects. Spatially, the planar mineralization bears northeasterly in the Graauwduinen West orebody, strikingly perpendicular to the southeasterly trend observed in the Graauwduinen East orebody. Contrasts in their bulk chemistry and mineralogy are statistically significant. The Graauwduinen West orebody features noticeably better total heavy mineral grades, accompanied by conspicuously high proportions of the gangue minerals garnet and pyroxene. The valuable mineral fraction is predominated by ilmenite (FeTiO3), followed in abundance by zircon (ZrSiO4), leucoxene (an alteration product of ilmenite), and rutile (TiO2). Their geochemistry, mineralogy, and petrography are extremely variable, but the bulk of the current valuable mineral fraction is recoverable to premium-grade products. The proximal, Mesoproterozoic Namaqualand Metamorphic Province is considered the main contributor to the current heavy mineral population. The Graauwduinen West orebody received source sediment via established fluvial-marine courses, whereas the source of the Graauwduinen East orebody is considered to originate from a distinct fluvial-aeolian corridor. The genesis of the Namakwa Sands deposit is strongly entrenched in the geomorphic evolution of the west coast of southern Africa since the Cenozoic, which was driven by regional tectonism, fluctuating sea levels, and alternating climatic patterns.

Diagnosing southeast tropical Atlantic SST and ocean circulation biases in the CMIP5 ensemble

Warm sea-surface temperature (SST) biases in the southeastern tropical Atlantic (SETA), which is defined by a region from 5°E to the west coast of southern Africa and from 10°S to 30°S, are a common problem in many current and previous generation climate models. The Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble provides a useful framework to tackle the complex issues concerning causes of the SST bias. In this study, we tested a number of previously proposed mechanisms responsible for the SETA SST bias and found the following results. First, the multi-model ensemble mean shows a positive shortwave radiation bias of ~20 W m−2, consistent with models’ deficiency in simulating low-level clouds. This shortwave radiation error, however, is overwhelmed by larger errors in the simulated surface turbulent heat and longwave radiation fluxes, resulting in excessive heat loss from the ocean. The result holds for atmosphere-only model simulations from the same multi-model ensemble, where the effect of SST biases on surface heat fluxes is removed, and is not sensitive to whether the analysis region is chosen to coincide with the maximum warm SST bias along the coast or with the main SETA stratocumulus deck away from the coast. This combined with the fact that there is no statistically significant relationship between simulated SST biases and surface heat flux biases among CMIP5 models suggests that the shortwave radiation bias caused by poorly simulated low-level clouds is not the leading cause of the warm SST bias. Second, the majority of CMIP5 models underestimate upwelling strength along the Benguela coast, which is linked to the unrealistically weak alongshore wind stress simulated by the models. However, a correlation analysis between the model simulated vertical velocities and SST biases does not reveal a statistically significant relationship between the two, suggesting that the deficient coastal upwelling in the models is not simply related to the warm SST bias via vertical heat advection. Third, SETA SST biases in CMIP5 models are correlated with surface and subsurface ocean temperature biases in the equatorial region, suggesting that the equatorial temperature bias remotely contributes to the SETA SST bias. Finally, we found that all CMIP5 models simulate a southward displaced Angola–Benguela front (ABF), which in many models is more than 10° south of its observed location. Furthermore, SETA SST biases are most significantly correlated with ABF latitude, which suggests that the inability of CMIP5 models to accurately simulate the ABF is a leading cause of the SETA SST bias. This is supported by simulations with the oceanic component of one of the CMIP5 models, which is forced with observationally derived surface fluxes. The results show that even with the observationally derived surface atmospheric forcing, the ocean model generates a significant warm SST bias near the ABF, underlining the important role of ocean dynamics in SETA SST bias problem. Further model simulations were conducted to address the impact of the SETA SST biases. The results indicate a significant remote influence of the SETA SST bias on global model simulations of tropical climate, underscoring the importance and urgency to reduce the SETA SST bias in global climate models.

Eocene aridity in southwestern Africa: timing of onset and biological consequences

The Neogene history of the Namib Desert is reasonably well understood, thanks to the presence of abundant sediments and fossils in Namaqualand, the Sperrgebiet and the Namib-Naukluft Park. Hyper-arid desert has existed along the west coast of Southern Africa since the Early Miocene. It has been demonstrated on the basis of stable isotope studies of struthious eggshells and mammalian dental enamel, that throughout the Neogene winter rainfall regime occurred in the south and summer rainfall regime in the north, although the boundary zone between the two regimes fluctuated latitudinally by several hundred kilometres through the Miocene. The pre-Miocene geological history of the region is much less well understood.The aim of this contribution is to discuss the palaeoclimate and palaeoenvironment of the richly fossiliferous pre-Miocene deposits related to the recently recognised Lutetian-Bartonian Ystervark Carbonatite Formation in the Sperrgebiet, with a view to throwing light on the development of arid climatic conditions in the subcontinent during the Palaeogene, and the consequences that aridification had on the Southern African biota. In pre-Bartonian time the climate in the Sperrgebiet was relatively humid and tropical with summer rainfall, but by Bartonian time there were signs of increasing aridity and a switch to predominantly winter rainfall was achieved by the Aquitanian. Fluctuations in groundwater levels were driven by the rise and fall of sea levels, resulting in alternating cycles of erosion and deposition in the zone along the coast.

The evolution of seabirds in the Humboldt Current: new clues from the Pliocene of Central Chile.

BackgroundDuring the last decade, new Neogene fossil assemblages from South America have revealed important clues about the evolution of seabird faunas in one of the major upwelling systems of the world: the Humboldt Current. However, most of this record comes from arid Northern Chile and Southern Peru and, in consequence, our knowledge of the evolutionary history of seabirds in the temperate transitional zone is negligible. A new Late Pliocene assemblage of fossil birds from the coastal locality of Horcon in Central Chile offers a unique opportunity to fill this gap.Principal FindingsIsolated bones of a medium-sized penguin are the most abundant bird remains. Morphological and cladistic analyses reveal that these specimens represent a new species of crested penguin, Eudyptes calauina sp. nov. Eudyptes is a penguin genus that inhabit temperate and subantarctic regions and currently absent in central Chile. Additionally, a partial skeleton of a small species of cormorant and a partial tarsometatarsus of a sooty shearwater have been identified.Conclusion/SignificanceThe Horcon fossils suggest the existence of a mixed avifauna in central Chile during the Pliocene in concordance with the latitudinal thermal gradient. This resembles the current assemblages from the transitional zone, with the presence of species shared with Northern Chile and Southern Peru and a previously unrecorded penguin currently absent from the Humboldt System but present in the Magellanic region. Comparison of Pliocene seabird diversity across the Pacific coast of South America shows that the Horcon avifauna represents a distinctive assemblage linking the living faunas with the Late Miocene ones. A comparison with the fossil record near the Benguela Current (west coast of southern Africa) suggests that the thermic gradient could play an important role in the preservation of a higher diversity of cold/temperate seabirds in the Humboldt Current.

The Influence of Inherited Structures on Dike Emplacement during Gondwana Breakup in Southwestern Africa

A kinematic analysis of Cretaceous and pre-Cretaceous structures was carried out along the west coast of southern Africa extending from the Cape Town area into Namibia with the aim of investigating whether inherited structural discontinuities controlled Gondwana breakup and the associated opening of the South Atlantic in the Cretaceous. This was augmented by map and satellite image analyses of mainly Cretaceous mafic dikes exposed from SW Angola to the southern tip of Africa. The combined results provide consistent evidence of E-W- to NE-SW-directed extension during the Cretaceous. E-W extension dominated from southern Angola to the Namibian–South African border, and NE-SW-directed extension occurred in an area extending from west-central Namibia to the southwestern coast of South Africa. These two extension directions overlap from west-central Namibia to southernmost Namibia. The kinematic analysis of Pan-African structures provides evidence of ENE-WSW-directed shortening in the western Saldania Belt in SW South Africa and ENE-WSW- to ESE-WNW-oriented constriction in the Gariep Belt near the border between South Africa and Namibia. Thus, the Pan-African shortening directions that led to the Late Neoproterozoic/Early Cambrian amalgamation of SW Gondwana are parallel to the main extension directions during Early Cretaceous Gondwana breakup and the initiation of South Atlantic rifting in southwestern Africa. This implies that opening of the modern South Atlantic was controlled by Pan-African (or older) structural discontinuities that were reutilized during the Early Cretaceous. The inherited structural basement anisotropies, which are generally parallel to major lineaments and/or crustal-scale shear zones, apparently controlled dike emplacement in the Early Cretaceous and the location of rifting at that time.

Changes in biological traits of macro-benthic communities subjected to different intensities of demersal trawling along the west coast of southern Africa

Biological traits analysis (BTA) is considered to be a powerful technique for describing the ecological functioning of marine benthic assemblages. This study is the first to apply BTA to assess differences in the traits of benthic faunal assemblages between areas exposed to heavy and light trawling in a major upwelling ecosystem along the west coast of southern Africa. The data were collected from two sampling locations in Namibia and six sampling locations in South Africa. The intensity of trawling varied from area to area. Significant differences in biological traits (BT) were detected between heavily and lightly trawled areas. Weighted infaunal traits showed significant differences between heavily and lightly trawled areas for 17% of the traits investigated, while 24% of epifaunal traits investigated were significantly different between areas of different trawling intensities. This suggests that the measured BTs of the epifauna might be more sensitive to trawling disturbances than BTs of the infauna. The infaunal traits differed significantly between areas with larger or smaller proportions of sand and mud. Nevertheless, more of the significant differences in infaunal BTs were related to variations in trawling intensity than to variations in sediment composition. Significant modifications of BTs are likely to lead to modified functioning of the community and provide more general potential indicators for management than those based on species. The study confirms the need for more basic biological and life history data on macro-benthic invertebrates but nevertheless shows that BTA detected specific features that correlate with trawling intensity and that these features may be important for epifaunal assemblage functioning.

Ensuring the future of the Namib's biodiversity: Ecological restoration as a key management response to a mining boom

The Namib Desert is an ancient desert on the west coast of southern Africa. The Namib has unique endemic biodiversity and scenic landscapes, with a major part contained in the Namib Naukluft Park and the adjacent Dorob National Park, together forming a major tourism attraction in Namibia. There are currently large exploration and mining developments in the central Namib, fuelled by rising global demand for uranium. Mining contributes significantly to the Namibian GDP, but through destruction of habitats and ecological processes, may cause environmental degradation and loss of ecosystem services. Additionally, Namibia stands to lose a significant part of the biological diversity that makes it unique. These direct impacts are occurring in the context of regional climatic changes that are predicted to have their own severe impacts on biodiversity. A number of tools exist to counter these impacts, among which ecological restoration is an important one. Yet the extent of the damage to ecological processes and functions of the Namib, the interactions with climate change and the mechanisms through which the impacts will occur are still not well known. There is thus a crucial need for a better understanding of these arid ecosystems and their response to disturbance, to devise better restoration techniques, and to inform decision makers about management options. This paper analyses the extent of the threats to the central Namib's ecosystems and biodiversity due to mining, identifies critical knowledge gaps for restoration, defines policy needs, and proposes a broad strategy which is intended to be a framework for research, planning and management for sustainable use of this unique desert.

Sea surface temperature in False Bay (South Africa): Towards a better understanding of its seasonal and inter-annual variability

Two sea surface temperature (SST) products, Pathfinder version 5.0 and MODIS/TERRA are evaluated and used to study the seasonal and the inter-annual variability of sea surface temperature (SST) together with local SST and wind data in the vicinity of False Bay (Western Cape, South Africa). At the monthly scale, differences of up to 3°C are detected between the two products in the bay. In the northern half of the bay, SST is fairly well explained by seasonality. In contrast, the southern half exhibits a higher inter-annual variability in SST. The southern half of the bay and the Western Cape upwelling system (Cape Agulhas to Cape Columbine) share most of their variance. Furthermore, the inter-annual variability of SST in False Bay is correlated with both the Niño 3.4 index and local wind speed anomalies. El Niño (La Niña) events induce an equatorward (poleward) shift in the South Atlantic High pressure system leading to a weakening (strengthening) of upwelling favourable south-easterly. Those changes induce a warm (cold) SST anomaly along the West Coast of Southern Africa.

The seaweeds of Angola: the transition between tropical and temperate marine floras on the west coast of southern Africa

The seaweed flora of Angola is relatively poorly known. Most of the 124 records listed for the country come from a 1974 British Natural History Museum expedition to the central and southern parts of that country. Previous biogeographic studies treated the Angolan seaweed flora as a whole and grouped it with those of certain West African islands as transitional between a Tropical West African seaweed flora (essentially extending from Senegal to Gabon) and temperate floras to the north and south of this truly tropical region. In the present study a total of 99 species and subspecies of seaweeds was collected from the intertidal zone and shallow sublittoral zones at five sites in the north of Angola and four sites in the south. The biogeographic distributions of our records were examined and compared with the temperate flora of Namibia to the south and the flora of Ghana to the north (as an example of a well-studied Tropical West African flora). Multivariate analyses of our presence/absence records showed differences between northern and southern sites (cluster analysis [Jaccard, average linkage] and detrended correspondence analysis). All Angolan sites were clearly different from floras of south, central and northern Namibia, which are considered to be strictly temperate in nature. Northern Angolan sites grouped more closely with Ghana than with southern Angolan sites. Distribution patterns within Angola are discussed in relation to monthly sea surface temperature data that were processed for this region. We conclude that the overall affinities of the Angolan seaweed flora, as represented by our collections, are Tropical West African, but with a well-developed temperate element in southern Angola (from about 13° S) comprising mainly cooler-water species from the Benguela Marine Province of Namibia and western South Africa. Our collections add about 45 species to the Angolan seaweed flora, raising the total number of species to around 169. This total approaches that of Ghana which, with about 200 species, is considered to have the richest seaweed flora in Tropical West Africa.