Estuarine species and habitat :distribution and connectivity

This study explored the distribution of estuarine macrophyte genetic lineages, species and habitats in relation to environmental gradients at various spatial scales. A database was assembled to determine the area and species composition of different estuarine habitats. This can now be used to retrieve information as a baseline for further monitoring and conservation planning. Research has shown that macrophytes occur over a wide range of physiochemical conditions, suggesting that these species have great genetic and phenotypic variation to occupy broad niche ranges. In eight estuaries along the South African coast, sediment and groundwater characteristics were measured in quadrants spanning the salt marsh, ecotone and terrestrial habitats. The results suggested that, in the absence of competition and disturbance at the salt marsh-terrestrial boundary, salt marshes would be unaffected by sea-level rise; and they would migrate landward. However, disturbance at the landward margin of salt marshes has already resulted in changes in species composition and altered environmental conditions. This promotes the encroachment of terrestrial alien invasive plants, leading to a loss of connectivity. A holistic assessment of land-cover changes showed that only 28% of South African estuaries still remain in a natural state. The delineation of all estuaries needs to be consistent and inclusive of all estuarine physical and biological processes, to curb future changes. The research results have been used in national assessments of estuarine health; and they have made a significant contribution to estuary-management plans. In addition, three scientific articles have been published from the thesis; and two more are currently under review