Southwestern Coast Of Africa Research Articles

Systematics, biogeography and conservation of Lactoridaceae

Abstract Lactoridaceae are a monotypic family confined to the Juan Fernandez (= Robinson Crusoe) Islands, Chile, an archipelago four million years old. Interest in the lone species, Lactoris fernandeziana , has increased in recent years due to its suspected role in early angiosperm evolution, as well as its endangered conservation status. Reports of fossil pollen of Lactoris (as Lactoripollenites ) from deep sea sediments of Cretaceous age off the western coast of South Africa provide evidence for southern hemisphere occurrence of the family 70–90 million years ago. This age, plus trimerous symmetry and simple morphology of the flower with three tepals, six stamens and three nearly free carpels with laminar placentation, involve the family with hypotheses regarding evolution of early angiosperms, especially paleoherb and monocot divergences. Based on cladistic analyses with morphological and nucleotide data, recommended taxonomic placement of Lactoris is as a monotypic order, Lactoridales, allied most closely to Aristolochiales, and also near Piperales. Approximately 1000 individuals of Lactoris are believed to exist, and genetic variation within and among populations as measured by isozymes and RAPDs is low. This, in part, could be due to the self-compatibility and geitonogamous breeding system of this wind-pollinated species. More efforts at ex situ conservation should be attempted so that this important angiosperm family is maintained for future evolutionary studies.

Rare earth elements in phosphorite and associated sediment from the Namibian and South African continental shelves

Rare earth elements (REE) and major elements have been determined in twenty-nine phosphorite and associated sediment samples from the southwestern coast of Africa, including thirteen samples of unconsolidated sediment collected during recent cruises to phosphate-rich areas on the Namibian shelf. The concentrations of REE in various phosphorite types from southwestern Africa differ by more than two orders-of-magnitude. The samples mostly exhibit REE patterns which are similar to that of shale, having no Ce anomaly. The Ce content appears to have been controlled by the palaeoredox conditions of the localised environment of deposition or diagenesis and not to have been influenced by marine upwelling, or by the general palaeoredox conditions of the water column. The environments in which REE were incorporated into the francolite appear to have been anoxic, or sub-oxic, in the case of both Namibian unconsolidated authigenic phosphorites, and the predominantly ‘diagenetic’ phosphorites off the South African coast. The ultimate REE source in both cases appears to have been (mainly eolic) continental detritus. Pelletal phosphorites are significantly enriched in REE relative to non-pelletal varieties. If sequestration of REE dissolved in the water column contributed to the high concentrations of REE in pelletal phosphorites, then the main carrier phase appears to have been inorganic detritus or biogenic silica equilibrated with oxygen-depleted bottom waters but not fish debris. The contention that onland phosphorites are enriched in REE relative to their offshore counterparts is, however, refuted in the case of southwestern Africa, and the effects of groundwater REE enrichment are not obvious in the majority of onland phosphorites analysed in this study.

The giant squid Architeuthis in southern African waters

Three specimens of the rare giant squid (genus Architeuthis, 18 nominal species) are described from the waters around southern Africa. Consideration of their internal and external morphology, including beaks, radula, statocyst and statolith give no reason to suppose that the three specimens do not pertain to the same species. A standardized data collection form and a summary of existing morphometric data are presented for the first time and the morphology and systematics of the genus are discussed. The value of various systematic characters is examined and certain guidelines are proposed, with an appeal for a more scientific approach to Architeuthis studies.Features of the internal anatomy, including the female reproductive tract, are described and illustrated and the beak dimensions are used to evaluate existing regression formulae for beak and body parameters. The statocyst and statolith are described and illustrated in full, the statolith for the first time, and are compared with those of other squids.The value of recent data from trawl‐caught specimens, as well as indirect evidence, is cited to replace speculation in discussions on distribution and habitat. Our specimens suggest that the waters off the south‐western coast of Africa may be one of the natural habitats of Architeurhis, during both feeding and spawning periods of the life cycle.

A preliminary investigation of the feeding ecology of skates (Batoidea: Rajidae) off the west coast of southern Africa

The diets of 14 species of skates (Rajiformes: Rajidae) collected along the coast of South-Western Africa between Walvis Bay and Cape Agulhas over a depth range of 50–1 016 m were analysed. Two distinct communities of skates could be recognized on the basis of depth zonation, the boundary between these communities being at approximately 380 m water depth. These two skate communities have similar species components: the so-called biscuit skate community (the shallow one) has two crustacean specialists (Cruriraja parcomaculata, Raja wallacei), one fish specialist (R. alba) and two generalists (R. pullopunctata, R. cf. clavata); the so-named grey skate community has two crustacean specialists (Raja caudaspinosa, R. confundens) and two generalists (Bathyraja smithii, R. leopardus). The grey skate community appears to be a more complex and dynamic assemblage with higher diversity (at least 13 species) than the biscuit skate community (five species). In both communities the most common prey items were crustaceans and small demersal fish. Cephalopods and polychaetes were uncommon prey in most species. Other potential prey items commonly trawled but absent from the skates' diet included bivalve molluscs, gastropods and echinoderms. Although their importance has hitherto not been recognized, skates are important predators on the demersal crustacean and fish fauna in the Benguela ecosystem.

Comments on “Rainfall Variability in Equatorial and Southern Africa: Relationships with Sea Surface Temperatures along the Southwestern Coast of Africa”

Abstract This article presents the results of an analysis of sea surface temperature (SST) fluctuations in the upwelling region along the Benguela coat and its relationship to rainfall variability both along the coast and throughout equatorial and southern Africa. The analysis incorporates compositing and time series analysis. Coastal rainfall is markedly enhanced during warm-water years and suppressed during cold-water years. The effects are strongest in March and April; at some stations, March totals of 50 mm in cold-water years contrast with 200 to 400 mm in March of warm-water years. Spectral analysis shows the variability of SSTs to be more pronounced on time scales of 5 to 6 years, and strong relationships with rainfall throughout equatorial and southern Africa are evident on this time scale. In coastal regions there may be some degree of direct local forcing of rainfall anomalies via SST anomalies, but the temporal and geographical patterns of the relationships suggest that in general, both SSTs an...

Physical and chemical conditions in an hypersaline spring in the Namib Desert

Hosabes is a small mineralized spring lying in a gypsous crust in the central Namib Desert on the south-western coast of Africa. It is fed by virtually fresh groundwater that wells to the surface at this and other similar fracture lines. The extremely high rates of evaporation and solar radiation result in intense concentration of the salts and the formation of strong salinity and therefore density gradients in the deeper parts of the system. These in turn produce a “solar pond” effect with a reversed temperature gradient; temperatures reach 50°C within the water column. The deeper parts of the system appear to be monomictic. Although the surrounding crust is largely gypsous, the water in the spring is dominated by NaCl as a result of precipitation of CaS04 in the highly concentrated water.

Rainfall Variability in Equatorial and Southern Africa: Relationships with Sea Surface Temperatures along the Southwestern Coast of Africa

Abstract This article presents the results of an analysis of sea surface temperature (SST) fluctuations in the upwelling region along the Benguela coat and its relationship to rainfall variability both along the coast and throughout equatorial and southern Africa. The analysis incorporates compositing and time series analysis. Coastal rainfall is markedly enhanced during warm-water years and suppressed during cold-water years. The effects are strongest in March and April; at some stations, March totals of 50 mm in cold-water years contrast with 200 to 400 mm in March of warm-water years. Spectral analysis shows the variability of SSTs to be more pronounced on time scales of 5 to 6 years, and strong relationships with rainfall throughout equatorial and southern Africa are evident on this time scale. In coastal regions there may be some degree of direct local forcing of rainfall anomalies via SST anomalies, but the temporal and geographical patterns of the relationships suggest that in general, both SSTs an...

MEASUREMENT OF SUSPENDED SEDIMENT IN THE SURF ZONE

The sea is an important source of water for cooling and other industrial purposes. From practical considerations, the water is usually drawn from a zone close to the shore, perhaps within one or two kilometres of the shore line through an intake structure such as a tunnel, pipeline or harbour or some comhination of these. If the coast is exposed to strong ware action and the local sea bed is of a sandynature, sediment will he lifted into suspension "by the oscillatory motion induced by the waves, and thus any sea water transported to the shore will contain a sediment load. This sediment content may have an adverse effect on the operation of the intake structure in various ways. If the water velocity is maintained at a high enough value throughout to avoid deposition, then the sand water mixture will tend to abrade the surface with which it is in contact. If however the water velocity is permitted to fall below the deposition value, sediment accumulation will occur which may be intentional as in a settling basin (requiring regular dredging or other removal) or inadvertent as in a pipe conduit (leading to partial blockage of the pipe). The writer has been associated with two sea water intake schemes, one on the western coast of South Africa, being a cooling water supply for a nuclear power station with a water consumption of about 100 m3/s; the other an intake for the recovery plant of a mining company in Namibia, water capacity about 1 m3/s. In both cases, information was needed concerning the variation of sediment concentration with distance above the sea bed, this distribution being measured at selected distances from the shore line. This led to a review of available techniques for determining the sediment content of sea water, and thence to development of new procedures and instruments. The details of these developments are presented in this paper.

SEABIRDS OFF THE SOUTHWESTERN COAST OF AFRICA

Summary Summerhayes, C. P., Hofmeyr. P. K. & Rioux, R. H. 1974. Seabirds off the southwestern coast of Africa. Ostrich 45: 83–109. The distribution of seabirds off the southwestern coast of Africa was observed during April. May and November, and observed south of Africa in March. Most seabirds off the west coast were concentrated near to the coast or over the edge of the continental shelf. These are sites where forms of upwelling bring water rich in nutrients to the surface of the sea. The most birds were seen in March, April and May, the least in November. Most common over the shelf-edge were, in order of abundance, Blackbrowed Albatross, Cape Hens, Shy Albatross, Yellownosed Albatross, Wilson's Storm Petrels, Cape Gannets, Common/Arctic Terns, and Antarctic Skuas. Seasonal shifts in their ranges and population densities probably reflect the influence of breeding and migration. Comparable concentrations of seabirds were only seen as the cold, nutrient-rich waters of the Subantarctic were approached south...