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Masters Degrees (Marine Biology)

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Browsing Masters Degrees (Marine Biology) by Author "Forbes, Anthony Tonks."

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    Association of juveniles of four fish species with sandbanks in Durban Bay, KwaZulu Natal.
    (1994) Graham, M. A.; Forbes, Anthony Tonks.; Cyrus, Digby Paul.
    Estuaries in South Africa are important nursery areas for the juveniles of many fish species. The condition of many of these systems has, however, deteriorated as a result of degradation caused by urban, industrial and agricultural development. An assessment of the role of harbours, particularly in KwaZulu Natal, as nursery grounds has therefore become an important issue. Durban Bay has undergone considerable changes since the mid-1800s and further developments are proposed. If these developments continue, they will result in the loss of large areas of the sandbanks, but Portnet has recognised the need to integrate environmental considerations into future port developments and operations. It was the overall aim of this study to establish the nature of the association of the juveniles of four common fish species viz. Pomadasys commersonnii, Gerres filamentosus, Liza dumerilii and Leiognathus equula with these sandbanks and, thereby assess the impact of their removal. It was found that all species were abundant on the sandbanks and that the diets of P. commersonnii, G. fiiamentosus and L. equuia were very similar, consisting primarily of bivalve siphon tips, benthic crustaceans and polychaetes. The respective contributions of each food type to the diet varied with species. The diet of L. dumerilii differed from that of the other three species, consisting primarily of benthic floc, foraminiferans, ostracods and sponge spicules. Despite differences in selectivity, it was concluded, from studies of the benthos in the harbour, that all four species, irrespective of size, were feeding on these sandbanks, as opposed to in the channels, throughout the year. Removal of the sandbanks for the construction of a new pier would, thus, result in the elimination of important feeding grounds for the juveniles of these four species.
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    The macrobenthos of the Little Lagoon, Durban Bay.
    (2002) Pillay, Deena.; Forbes, Anthony Tonks.
    The Little Lagoon is a shallow sandflat habitat situated in Durban Bay, which has been earmarked for removal, as part of the port expansion. In order to prevent the possible loss of such a significant habitat, it was proposed that this habitat be re-created elsewhere in the Bay. The aims of this project were therefore to provide a detailed assessment of the macrobenthic habitat of the Little Lagoon, and to identify the major determinants of the community structure. The ultimate goal was to provide essential background information to assess the success of the recreation of the Little Lagoon. Apart from seasonal changes in water temperature, no ecologically significant temporal fluctuations in the physical environment of the Little Lagoon were detected. This was directly translated into an extremely stable macrobenthic community, in which negligible seasonal changes to its composition were recorded. The polychaetes Prionospio sexoculata, Glycera sp, the isopod Leptanthura laevigata and cumaceans dominated the community during every sampling season. From a spatial perspective, particle sizes and organic contents of surficial sediments were the major determinants of macrobenthic community structure. Densities of macrofauna were three to five times higher in organically rich sediments, and were dominated by surface and sub-surface deposit feeders such as the tanaid Apseudes digitalis and cirratulid polychaetes. In organically poor sediments, burrowing infauna such as Prionospio sexoculata and Glycera sp. dominated. Significantly though, biological interactions, specifically bioturbation by the sandprawn Callianassa kraussi, was an important determinant of community structure in the Little Lagoon. Two zones of high and low abundance of C. kraussi were recorded in the Little Lagoon. Abundance, species richness and diversity of macrofauna were significantly lower in the zone of high C. kraussi abundance. These parameters were significantly and negatively influenced by the abundance of C. kraussi, indicating that C. kraussi may act as a disturbance organism. Surface dwelling macrofauna were recorded in the zone of low C. kraussi abundance, but not in the zone of high C. kraussi abundance. It appeared that the bioturbative activity of C. kraussi of expelling sediment from burrows to the sediment surface resulted in the exclusion surface dwelling fauna, and played a major role in structuring the Little Lagoon macrobenthic community.