Life history, circulation and maintenance of Nyctiphanes capensis (Euphausiacea) in the northern Benguela upwelling system

13 pages, 9 figures, 1 table

[EN] Previous studies have shown that waters off central Namibia (22–23°S) support high concentrations (>20 adults·m) of large (>21 mm total length) Nyctiphanes capensis, die dominant euphausiid species over the shelf of the northern Benguela upwelling system. The population dynamics of the species was investigated in order to provide some insight into the mechanisms involved in maintaining such concentrations of unusually large individuals in the region. It is postulated that bottom topography and coastline orientation determine a semi-enclosed circulation pattern, characterized by reduced upwelling, strong stratification of the water column and convergence. In this environmental scenario, N. capensis would benefit from the relatively high and less variable (compared to other areas) phytoplankton concentrations derived from this circulation pattern. The hypothesis is that this adequate environment would result in longer residence times of N. capensis and would increase its reproductive rates. Selected past and new observations are presented and discussed in relation to this hypothesis. The role of the poleward flow that typically develops over the shelf between January and April in transporting new individuals into the region, and the dispersal of early reproductive products in the wind-driven upper layer, are also discussed. © 1992 Taylor & Francis Group, LLC.

Vorige studies het aangetoon dat die waters teenoor sentrale Namibie (22-23°S) hoe konsentrasies (> 20 volwassense' m-3) onderhou van groot (>21 mm totale 1engte) Nyctiphanes capensis. die oorheersende eufausiïede spesie oor die vastelandsplat van die noordelike Benguela-opwelstelsel. Die bevolkings-dinamika van die spesie is ondersoek om 'n mate van insig te verskaf oor die meganismes waarvolgens sulke konsentrasies ongewoon groot individue in die streek gehandhaaf word. Daar word gepostuleer dat bodemtopografie en kuslynoriëntasie 'n halfgeslote stroompatroon bepaal, gekenmerk deur verminderde opwelling, sterk laagvorming van die waterkolom en konvergensie. In hierdie omgewingscenario sal N. capensis voordeel trek uit die betreklik hoe en minder wisselende (in vergelyking met ander gebiede) fitoplanktonkonsentrasies afkomstig van hierdie stroompatroon. Die hipotese is dat hierdie toereikende omgewing langer verblyf duUTvan N. capensis tot gevolg sou he en sy voortplantingstempo sou versnel. Gekeurde vorige en nuwe waamemings word aangebied en bespreek in verband met hierdie hipotese. Die rol van die poolwaartse vloei wat tipies oor die plat tussen Januarie en April ontwikkel, in die invoer van nuwe individue na die streek, en die verstrooiing van vroee voortplantingsprodukte in die windgedrewe boonste laag word ook bespreek