Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 176-201).

Thesis (M. Env. St.)--University of Adelaide, Mawson Graduate Centre for Environmental Studies, 1993. / Includes bibliographical references (p. 86-93).

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Mangrove forests provide a suite of critical ecosystem services ranging from local to global scales.Soil conditions and associated micro-organisms play a fundamental role in maintaining these services, that include nutrient cycling, carbon sequestration and plant growth-promoting properties. Despite its importance, the microbial abundance and function of mangrove soil has received little effort in current research. On the ecotone between the land and the sea, mangrove soils are subject to high variability of geomorphological and ecological conditions that imply a strong distinction of ecological niches. These conditions can diversify the structure and function of the prevalent microbiome. To identify the structure of bacterial communities of mangrove soils, 16S rRNA gene sequencing techniques were applied on samples from arid Avicennia marina forests across different spatial scales: (i) at different depths of the soil profile(surface/subsurface); (ii) between two distinct zones within a given forest (seaward/landward); (iii) among forests with varying local hydrodynamic conditions (exposed/sheltered); and (iiii) among forests in different geographic regions (Saudi Arabia and Australia). This study found that the bacterial soil community varied more within each forest than between forests in different countries. Notably, differences between countries became more apparent at the finest taxonomic resolution (ASVs). Bacterial communities from the landward zone of the mangrove forest are more conserved across countries than those from the dynamic seaward zone. Theoretically assigned functions showed high levels of sulfate respiration and chemoheterotrophy as major metabolic pathways. Differences across local factors in the functional traits reflect the within forest variability. The distinct microbial assemblages from the landward zone were associated with high salinity and phosphorus, and nitrogen and larger grain size were associated with the seaward samples. Understanding patterns of microbial communities in mangrove soils is important to predict changes and mitigate anthropogenic pressures on the ecosystem.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Thesis (M.Sc.). / Written for the Dept. of Geography. Title from title page of PDF (viewed 2008/12/04). Includes bibliographical references.

Thesis (Ph.D.) -- James Cook University, 2003. / Typescript (photocopy) Bibliography: leaves 214-238.

Thesis (Ph. D.)--Adelaide University, 2003. / Title from PDF title page (viewed on May 1, 2005). Includes bibliographical references (p. 135-152).

Thesis (M.Sc.). / Written for the Dept. of Geography. Includes bibliographical references.

Mangroves in South Africa are prone to anthropogenic pressures such as browsing and trampling by livestock and by natural disturbances such as drought and floods. These mangroves exist at one of the most southerly limits in the world providing a unique opportunity to study recovery and resilience to change. This study used long term data at three South African study sites located in the subtropical (St Lucia Estuary) and warm temperate regions (Nxaxo and Kobonqaba estuaries) to compare mangrove growth rate, population structure and responses to disturbance. The first objective was investigated at St Lucia Estuary where site specific or microhabitat differences were measured to assess the influence of these on mangrove growth and population structure. It was suggested that site - specific variability would ensure mangrove survival and analysis showed that seedlings were present at different sites in different years. There was always some recruitment but often little survival to the next size class. Over time seedling numbers were quite variable and self – thinning of adults was evident. The second objective was to identify the environmental factors influencing population density and growth. Results showed that sediment moisture and salinity influenced seedling and adult density due to fluctuations in estuary water level. Mangrove growth rates for Avicennia marina in terms of height was faster (40 – 75 cm yr-1 ) at Site 1 where conditions were waterlogged and moderately saline and slower (5 – 25 cm yr1 ) in dry and hypersaline conditions at Site 4. Overall mangroves at St Lucia have shown persistence through drought and fluctuations in environmental conditions however resilience may be hindered at sites that are subjected to partially flooding and prolonged waterlogging. The second site was Nxaxo Estuary in the Eastern Cape where cattle exclusion plots (nonbrowsed) and control plots (browsed) were used to assess the recovery of A. marina trees from cattle browsing. Trees in the browsed plots showed no vertical growth while trees in the non-browsed plots grew significantly faster (5.4 ± 0.5 cm yr-1). When cattle were prevented from entering the mangrove area, the trees recovered fairly quickly and within 3 years growth was similar in both the non – browsed (17.9 ± 3.2 cm yr -1) and browsed plots (18 ± 1.6 cm yr -1). Lastly, mangrove recovery was investigated at Kobonqaba Estuary where long-term closure of the mouth to the sea resulted in high water levels, inundation of pneumatophores and die-back of the majority of the mangroves. This study measured the recovery of the mangroves by assessing changes in vegetation cover and sediment characteristics along transects. High initial porewater nutrient concentrations promoted salt marsh growth and plants increased average cover from 0% in 2011 to 18.9% (2013) and 50% in 2015. The total number of A. marina individuals increased from only seven to 27 individuals over four years. Salt marsh competition and facilitation will likely influence mangrove recovery in the future. Overall it was concluded that when a short term pressure (cattle browsing) is alleviated, mangrove forests even at warm temperate sites are able to recovery rapidly by increasing growth and seedling establishment. However, mangroves in the subtropical sites show more resilience and recovery potential to long term pressures such as fluctuating environmental conditions because of faster growth rates.