The results of a community survey of the rocky intertidal and subtidal reef ichthyofauna of the Tsitsikamma National Park and adjacent areas are presented. An updated species checklist is given, comprising 116 species of 46 families, including a new genus and species of Tripterygiid. Single species are shown to dominate, in terms of numbers, both the cryptic and subtidal components for all the areas sampled down the vertical profile. Species richness, evenness and diversity are found to increase with depth for both the cryptic and suprabenthic components. A community level feeding study shows an increase in trophic specialisation with depth and food availability is found to be an important factor delimiting littoral fish vertical distribution. The nursery function of the Tsitsikamma rocky littoral area is assessed and it is shown that shallow littoral areas as a whole are more important than intertidal pools alone in functioning as nurseries. The results of the study are found to fit into the existing trend of an increase in species richness and diversity, from west to east, along the South African coast. A significant difference is shown between the observed frequencies of species on exploited reefs outside the Park and unexploited reefs inside the Park. The density of the key reef predator Petrus rupestris is shown to be nine times more abundant on deep reef inside the park compared to deep reef outside the park (0.0045 fish/m² and 0.0005 fish/m² respectively) and a paucity of larger individuals of this species on exploited reefs is noted. Marked differences in the relative abundance of other species between exploited and unexploited reefs are evident and it is hypothesised that community disruption has occurred on exploited reefs, either directly or indirectly because of the removal of P. rupestris. These results are discussed in the context of marine reserves as a conservation strategy and a recommendation is made to extend the 5.6km seaward boundary of the Tsitsikamma National Park westwards to include the large concentration of presently exploited rocky reefs between the Blaaukrans river mouth and Natures Valley.

Thesis (PhD. (Botany)) - Rhodes University, 2008

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 188-212).

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The goal of this thesis was to examine submerged macrophoe biomass, distribution, and ecosystem effects at scales large enough to incorporate the littoral zone into models of whole lake structure and function. Submerged macrophyte biomass and distribution was shown to be highly variable between growing seasons and primarily dependant upon air temperature and the timing of the onset of the growing season. Within a growing season, a mass balance study showed an undisturbed macrophyte bed to markedly lower phytoplankton biomass: total phosphorus ratios, although the net effect of the bed on the growing season phosphorus budget was minimal. The weedbed preferentially retained phytoplankton biomass while being a source of bacterial production to the open water. These findings were mirrored at the among lake scale, as planktonic respiration and bacterial production were higher in macrophyte dominated lakes than would be expected based on phytoplankton biomass alone. Further, phytoplankton biomass was lower than would be expected based on epilimnetic phosphorus levels, showing that the classical view of pelagic interactions that proposes phosphorus determines phytoplankton abundance, which in turn determines bacterial abundance through the production of organic carbon, becomes less relevant as macrophyte cover increases. Long term phosphorus accumulation in the littoral zone was shown to be linked to macrophyte biomass, and on average almost an order of magnitude higher than calculated from the growing season (June--October) phosphorus budget, suggesting that the bulk of phosphorus accumulation in weedbeds occurs outside of the growing season. Finally, sediment core data showed that while submerged weedbeds accumulate up to four times as much bulk sediment compared to the profundal zone, phosphorus accumulation in weedbeds is much less than observed in the profundal zone. These results strongly indicating that submerged macrophyte beds play a central role in trapping ep

When considering the large amount of work done on dune ecology, and that a number of the classical ecological theories originate from work on dunes, it is apparent that there remains a need for physiological and mechanistic explanations of dune plant phenomena. This thesis demonstrated that in the extreme coastal environment dune plants must survive both high rates of burial (disturbance), and low nutrient availability (stress). The ability of four species to respond to these two factors corresponded with their position in a vegetation gradient on the dunes. A low stem tissue density was shown to enhance the potential stem elongation rate of buried plants, but reduced the maximum height to which a plant could grow. Such a tradeoff implies that tall light-competitive plants are able to survive only in stable areas, while burial responsive mobile-dune plants are limited to areas of low vegetation height. This stem tissue density tradeoff was suggested as the mechanism determining the zonation that species show within the dune vegetation gradient present at various sites in South Africa. Finally, detailed investigations of dune plant ecophysiology found that: 1) The resources used in the response to burial derive from external sources of carbon and nitrogen, as well as simple physiological and physical mechanisms of resource allocation. 2) The leaves of dune plants were found to be operating at one extreme of the photosynthetic continuum; viz efficient use of leaf nitrogen at the expense of water loss. 3) Contrary to other ecosystems, the environmental characteristics of dunes may allow plants to occupy a high disturbance, high stress niche, through the maintenance of lowered competition. 4) At least two mobile-dune species form steep dunes, and are able to optimise growth, on steeper dunes, such that they have to grow less in response to burial than plants that form more shallow dunes. In this thesis, it was shown that the link between the carbon and nitrogen economies of dune plants was pivotal in determining species distributions and survival under extreme environmental conditions. As vast areas of the world’s surface are covered by sand dunes these observations are not just of passing interest.