https://commons.ru.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:6910 Wed 08 May 2024 19:10:29 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6548 Tue 07 May 2024 10:07:02 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6933 20 μm) species composition and distribution along a repeat transect between Cape Town and the Prince Edward Islands were investigated in early austral autumn (April/May) 1996. Samples were collected at approximately 30 nautical mile intervals for the analysis of size-fractionated chl-a and the identification and enumeration of microphytoplankton species. Peaks in total chl-a (>1 μg 1 [superscript -1]) were recorded at the Subtropical Convergence (STC), at the Sub-Antarctic Front (SAF) and in the waters surrounding the Prince Edward Islands. In addition, a minor peak in chl-a concentration was recorded in the continental shelf waters. At stations where elevated chl-a concentrations were recorded, microphytoplankton generally formed a substantial contribution (-10%) to total chlorophyll. Outside these regions, total chlorophyll concentrations were lower (<0.9 μg 1 [superscript -1]) and almost entirely dominated by nano- and picophytoplankton, which contributed >95% of the total. Microphytoplankton species composition along both transects were dominated by chain-forming species of the genera Chaetoceros (mainly C. neglectum, C. peruvianus and C. constrictus), Nitzschia spp. and Pseudoeunotia doliolus. Cluster and ordination analysis based on species composition identified five distinct microphytoplankton assemblages, which were closely associated with the different water masses in the region between Cape Town and the Prince Edward Islands. The microphytoplankton species composition and biogeographic zones identified during this investigation are in general agreement with similar studies conducted in the south-west Indian Ocean during the austral summer, which suggests that there are little seasonal trends in both the microphytoplankton species composition and biogeographic zonation.]]> Thu 25 Apr 2024 15:50:06 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6934 Thu 25 Apr 2024 15:49:41 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6935 Thu 25 Apr 2024 15:49:12 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6834 Thu 25 Apr 2024 15:47:55 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6901 Thu 25 Apr 2024 15:47:30 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6830 8.5°C, salinity >34.2), suggesting that the SAF lay extremely far to the south. In the southeast corner water masses were typical of the Antarctic zone, showing a distinct subsurface temperature minimum of <2.5°C. Total integrated chl-a concentration during the survey ranged from 4.15 to 22.81 mg chl-a m[superscript (-2)], with the highest concentrations recorded at stations occupied in the frontal region. These data suggest that the region of the South-West Indian Ridge represents not only an area of elevated biological activity but also acts as a strong biogeographic barrier to the spatial distribution of zooplankton.]]> Thu 25 Apr 2024 15:46:55 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6832 Thu 25 Apr 2024 15:46:11 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6569 Thu 25 Apr 2024 15:45:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6928 200 μm) was investigated on three occasions in a warm temperate, temporarily open/closed estuary situated along the southern African coastline. Results of the investigation indicated that the microheterotrophs represented the most important consumers of bacteria and chlorophyll (chl)-a <5.0 μm. The low impact of the mesozooplankton on the bacteria and chl-a <5.0 μm during the study appeared to be related to the inability of the larger zooplankton to feed efficiently on small particles. During those periods when total chl-a concentration was dominated by picophytoplankton (<2.0 μm) and microphytoplankton (>20 μm), mesozooplankton were unable to feed efficiently on the chl-a due to feeding constraints. In response to the unfavorable size structure of the phytoplankton assemblages, mesozooplankton appeared to consume the microheterotrophs. The negative impact of the mesozooplankton on the microheterotrophs resulted in a decrease in the impact of these organisms on the bacteria and the chl-a <5.0 μm. This result is consistent with the predator-prey cascades. On the other hand, when the total chl-a was dominated by nanophytoplankton (2–20 μm), mesozooplankton were able to feed directly on the phytoplankton. Results of the study indicate that size structure of the phytoplankton assemblages within estuaries plays an important role in mediating the trophic interactions between the various components of the plankton food web.]]> Thu 25 Apr 2024 15:44:49 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6965 Thu 25 Apr 2024 15:43:21 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6966 0.05). The zooplankton community was dominated, numerically and by biomass, by mesozooplankton comprising mainly copepods of the genera, Oithona,Paraeuchaeta, Pleuromamma, Calanus and Clausocalanus. An exception was recorded at those stations in the region of the front where the tunicate, Salpa thompsoni, dominated the total zooplankton biomass.]]> Thu 25 Apr 2024 15:42:47 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6881 Thu 25 Apr 2024 15:42:12 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6967 Thu 25 Apr 2024 15:41:41 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6886 Thu 25 Apr 2024 15:40:20 SAST ]]>