The study undertaken was an attempt to provide information on the effect that oceanographic features common in the Mozambique Channel have on primary production. Oligotrophic conditions dominated the Mozambique Channel at the time of sampling and the introduction of nutrients into the euphotic zone by upwelling processes were identified as cyclonic eddies. Differences in physico-chemical variables between surface and F-max across all sites proved to be stronger than the physico-chemical variables between 4 grouped oceanographic features. This was revealed by stronger variations in phytoplankton community structure and chlorophyll a concentration between surface and F-max compared to oceanographic features sampled. One of the hypotheses presented for the study was that diatoms would dominate phytoplankton communities within a cyclonic eddy. This was not the case as the coccolithophorid, Emiliania huxleyi Lohmann (Hay and Mohler 1967) dominated F-max and surface water in the cyclonic eddies and most other sites. Phytoplankton community structure did not differ significantly between the oceanographic features sampled which contradicted another one of hypotheses presented in the study. Chlorophyll a concentration in surface water of the cyclonic eddies was significantly higher than in surface waters within the anti-cyclonic eddy. F-max was not significantly different in phytoplankton biomass between these two system types. The cyclonic eddies and anti-cyclone had similar phytoplankton diversity which did not verify the hypothesis that there would be less phytoplankton species diversity within cyclonic eddies compared to the anti-cyclonic eddy. Phytoplankton community structure differed between F-max (depth at which maximum chlorophyll a is found) and the surface. This phytoplankton community difference was linked to differences in physico-chemical variables between the two depths. The diatoms Thalassionema nitzschioides, Pseudo-nitzschia sp.A, Pseudo-nitzschia sp.B, Thalassiosira sp.C, Thalassiosira sp.E, Bacteriastrum furcatum, Guinardia cylindrus, Nitzschia closterium, Hemiaulus hauckii, and Nitzschia braarudii revealed the only discernible ecological similarity amongst phytoplankton species across all sites and depths. This is important as it revealed that these species were regularly found occupying similar depths and potentially similar physico-chemical ranges in the water column which suggest these diatom species responded to a dominant source of variation. Distribution patterns of species and of ecologically defined groups support the hypothesis that diatom species and assemblages are good indicators of the changing character of an upwelling system. These statements lead to the assumption that the diatom grouping found in this study indicates areas of upwelling where water temperatures are reduced and nutrients are more readily available. One must keep in mind that ordination techniques are only descriptive and no significance is tested. The coccolithophorid D. anthos and the dinoflagellate Phalacroma spp. were noted as being most dissimilar to all other phytoplankton species with regards to their position in the water column and their response to physico-chemical variables. Finally, the dominance of E. huxleyi in the Mozambique Channel during November/December of 2009 reveals the potential vulnerability of phytoplankton in the channel to ocean acidification.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:10622 |
| Date | January 2012 |
| Creators | O'Reilly, Bevan James |
| Publisher | Nelson Mandela Metropolitan University, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | xiii, 106 leaves, pdf |
| Rights | Nelson Mandela Metropolitan University |
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