Reproduction of the sea urchins Echinometra mathaei and Diadema savignyi on the South African eastern coast

The reproductive cycles of Echinometra mathaei and Diadema savignyi on the South African eastern coast were investigated by means of gonad index and histological methods. Both species showed annual cycles, with spawning occurring during the summer months (December to March-April), but the degree of gametogenic synchrony differed markedly between the two species. In D. savignyi, gametogenesis within and between sexes was in close synchrony and there was evidence suggesting that repeated spawning with a monthly rhythm occurred. In contrast, gametogenesis in E. mathaei was poorly synchronized and spawning occurred over an extended period.

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Growth and movement of the South African abalone Haliotis midae: A reassessment

Marine and Freshwater Research ◽

10.1071/mf9950583 ◽

1995 ◽

Vol 46 (3) ◽

pp. 583 ◽

Cited By ~ 20

Author(s):

RJQ Tarr

Keyword(s):

South African ◽

Growth Rates ◽

Growth Parameters ◽

Eastern Coast ◽

Island Population ◽

Western Coast ◽

Eastern Cape ◽

The South ◽

Significant Difference ◽

Haliotis Midae

Growth rates of a number of Haliotis midae populations around the South African coast were studied by means of tagging. These populations ranged from the cool waters of the western coast to the more temperate environment of the eastern Cape. Standard von Bertalanffy growth curves were fitted and growth parameters derived. These ranged from 0.19 to 0.25 for K, the average rate at which L∞ is approached, and from 156 to 173 for L∞, the average theoretical maximum length. These indicate far higher growth rates than were previously published for this commercially fished species, and the reasons for this difference are discussed. The expectation that growth rates would be fastest in the warmer eastern Cape waters was not realized, there being no significant difference in growth between the Bird Island population on the eastern coast and the Robben Island population on the western coast. These new growth parameters indicate that H. midae in the commercial fishery grounds is attaining sexual maturity some four years earlier, and the minimum legal size some five years earlier, than previously considered. This has considerable significance for modelling studies presently underway. Movement of a small population of adult H. midae was studied over a three-year period, after which 47% of the original abalone were still present on the study site. Of these, 81.5% still occupied exactly the same position on the rocks. This indicates that H. midae that have located an optimum habitat, and that are not disturbed, tend not to move.

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The Rand and the Monetary Systems of Botswana, Lesotho, and Swaziland

The Journal of Modern African Studies ◽

10.1017/s0022278x00007849 ◽

1978 ◽

Vol 16 (1) ◽

pp. 97-121 ◽

Cited By ~ 10

Author(s):

Francis d'A. Collings

Keyword(s):

South Africa ◽

South African ◽

Extended Period ◽

National Currency ◽

The South ◽

Legal Tender ◽

Monetary System ◽

Monetary Systems ◽

The Creation

Botswana, Lesotho, and Swaziland are among very few countries which, in recent times, have for an extended period and without formal agreement used another national currency as their domestic circulating medium and legal tender. After many years of being de facto part of a larger monetary area using the South African currency, in 1972 the three smaller countries jointly initiated negotiations with Pretoria which led to the creation of an officially recognised Rand Monetary Area in December 1974. Thereafter they chose different arrangemènts which span the spectrum between continued integration with and separation from the monetary system of South Africa. The experiences of these countries, while of interest in themselves, may also be relevant to other governments with dependent currency systems which face similar options.

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Crustacea

Philosophical Transactions of the Royal Society of London ◽

10.1098/rstl.1879.0051 ◽

1879 ◽

Vol 168 ◽

pp. 485-496 ◽

Cited By ~ 2

Keyword(s):

New Species ◽

South African ◽

Eastern Coast ◽

Special Study ◽

The South ◽

East African ◽

East African Coast ◽

African Coast ◽

The Indian Ocean ◽

The Subject

The Crustacea collected by Messrs. G. Gulliver and H. H. Slater amount in all to 189 specimens, representing 35 species. All of these are forms that are widely distributed throughout the Indo-Pacific or Oriental Region (which includes the eastern coast of Africa, the south and east of Asia and islands adjacent, Australia, and the islands of Polynesia), with the following exceptions:— Atergatopsis signatus (hitherto only known from the Mauritius), Caridina typus (original locality not known), Palœmon dispar (hitherto recorded only from the Malayan Archipelago), Palœmon hirtimanus (from Mauritius, Réunion, and the Indian Ocean), P. debilis (from Amboina and the Sandwich Islands), and the new species of Talitrus ( T. gulliver i), which is described below. With two exceptions all the species in the collection belong to the Podophthalmia . The following are the sub-tribes represented, with the number of species belonging to each :— The Crustacea inhabiting the Red Sea have been made the subject of special study by Rüppell and Heller, those of Madagascar and the islands adjacent by Hoffmann, of Mauritius and Réunion by Alphonse Milne-Edwards, and of the South African coast by M’Leay and Krauss. Valuable additions to our knowledge of the Crustacea of the East African coast have been published by Hilgendorf, in Van der Decken’s “Reisen in Ost-Afrika,” where will also be found a conspectus of all the known species of East African Crustacea by Von Martens. So far as I am aware, however, no species have hitherto been recorded as inhabiting the Island of Rodriguez.

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Retroflection from a double-slanted coastline: a model for the Agulhas leakage variability

Ocean Science ◽

10.5194/os-6-997-2010 ◽

2010 ◽

Vol 6 (4) ◽

pp. 997-1011 ◽

Cited By ~ 2

Author(s):

V. Zharkov ◽

D. Nof ◽

W. Weijer

Keyword(s):

South African ◽

Mass Flux ◽

South Atlantic ◽

Eastern Coast ◽

The South ◽

Slant Angle ◽

Agulhas Current ◽

Low Leakage ◽

Nonlinear Analytical Model ◽

Kink Model

Abstract. The Agulhas leakage to the South Atlantic exhibits a strong anti-correlation with the mass flux of the Agulhas Current. When the Agulhas retroflection is in its normal position near Cape Agulhas, leakage is relatively high and the nearby South African coastal slant (angle of derivation from zonal) is very small and relatively invariant alongshore. During periods of strong incoming flux (low leakage), the retroflection shifts upstream to Port Elizabeth or East London, where the coastline shape has a "kink", i.e., the slant changes abruptly from small on the west side, to large (about 55°) on the east side. Here, we show that the variability of rings shedding and anti-correlation between Agulhas mass flux and leakage to the South Atlantic may be attributed to this kink. To do so, we develop a nonlinear analytical model for retroflection near a coastline that consists of two sections, a zonal western section and a strongly slanted eastern section. The principal difference between this and the model of a straight slanted coast (discussed in our earlier papers) is that, here, free purely westward propagation of eddies along the zonal coastline section is allowed. This introduces an interesting situation in which strong slant of the coast east of the kink prohibits the formation and shedding of rings, while the almost zonal coastal orientation west of the kink encourages shedding. Therefore, the kink "locks" the position of the retroflection, forcing it to occur just downstream of the kink. Rings are necessarily shed from the retroflection area in our kinked model, regardless of the degree of eastern coast slant. In contrast, a no-kink model with a coastline of intermediate slant indicates that shedding is almost completely arrested by that slant. We suggest that the observed difference in ring-shedding intensity during times of normal retroflection position and times when the retroflection is shifted eastward is due to the change in the retroflection location with respect to the kink. When the incoming flux detaches from the coast north of the kink, ring transport is small; when the flux detaches south of the kink, transport is large. Simple process-oriented numerical simulations are in fair agreement with our analytical results.

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Retroflection from a double slanted coastline – a model for the Agulhas leakage variability

Ocean Science Discussions ◽

10.5194/osd-7-1209-2010 ◽

2010 ◽

Vol 7 (4) ◽

pp. 1209-1244

Author(s):

V. Zharkov ◽

D. Nof ◽

W. Weijer

Keyword(s):

South African ◽

Eastern Coast ◽

East Side ◽

The South ◽

The West ◽

West Side ◽

Agulhas Current ◽

Nonlinear Analytical Model ◽

The Difference ◽

Kink Model

Abstract. The Agulhas leakage to the South Atlantic (SA) exhibits strong anti-correlations with the mass flux of the Agulhas Current. This is accompanied by the migration of the Agulhas retroflection whose normal position (NPR) is near Cape Agulhas, where the slant of the South African coast is very small. During periods of strong incoming flux (SIF), the retroflection shifts upstream to Port Elizabeth or East London, where the coastline shape has a "kink", i.e., the slant changes abruptly from small on the west side, to large (about 55°) on the east side. Here, we show that the variability of rings shedding maybe attributed to this kink. To do so, we develop a nonlinear analytical model for retroflection near a coastline that consists of two sections, one strongly slanted (corresponding to the east side) and the other zonal (corresponding to the west side). The principal difference between this and the model of a single straight slanted coast discussed in our earlier papers is that a free purely westward propagation of eddies along the zonal coastline section is allowed in the kinked case. This introduces the interesting situation where the strong slant of the coast east of the kink prohibits the formation and shedding of rings whereas the coast west of the kink encourages such shedding. Therefore, the kink model "locks" the position of the retroflection forcing it to occur just downstream of the kink. That is, rings are necessarily shed from the retroflection area in our kinked model, regardless of the eastern coast slant. By contrast, the application of "no-kink" model for an "averaged" slant (at the same point as the kink) leads to the conclusion that shedding is almost completely arrested by the slant. We suggest that the difference between the intensities of rings shedding during NPR and SIF is due to the shift in the zero curl line in respect to the kink. When the zero curl intersects the coast north of the kink the transport is small but it is large when the zero curl is situated south of the kink. Simple process-oriented numerical simulations are in fair agreement with our results.

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