京都大学 / 新制・課程博士 / 博士(地球環境学) / 甲第25474号 / 地環博第260号 / 新制||地環||53(附属図書館) / 京都大学大学院地球環境学舎環境マネジメント専攻 / (主査)教授 柴田 昌三, 教授 西前 出, 准教授 落合 知帆 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DGAM

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

Bibliography: p. 86-93.

Because of the variety of ecological and economic functions they perform, estuaries and mangrove swamps are recognised as amongst the most valuable habitats on earth. However, estuaries and related mangrove swamps are threatened by human expansion and exploitation which leads to changes in land cover change within and surrounding these sensitive ecosystems. Such land cover changes can either have desirable or undesirable effects on natural ecosystems. Examples of undesirable impacts of land cover change include soil erosion and degradation, the removal of indigenous vegetation for human development, and the pollution of water. Without an effective means of identifying, monitoring and managing land cover changes over time, these sensitive ecosystems face a bleak and uncertain future. The researcher sought to determine whether wetland bird species could be used as an effective method of monitoring the environmental health of estuaries and mangrove swamps. In particular, the research sought to determine whether analysing fluctuations in the populations of wetland bird indicator species, as evident in the CWAC Bird Census data, could assist in monitoring and assessing undesirable and desirable land cover changes within the Mgeni Estuary and Beachwood Mangrove Swamps. An examination of the archival aerial imagery of the study area for the years 1991, 1997, 2003 and 2008 provided by the University and private companies, revealed significant changes in land cover over the last two decades. The land cover changes identified represent an actual decline or increase in the suitable foraging, roosting or reproductive habitats of wetland bird indicator species within the study area. The research focused on investigating whether fluctuations in wetland bird populations can be correlated with the recorded changes in land cover over the last two decades. The research discovered a direct and comprehensive link between fluctuations in specific populations of wetland bird indicator species and the land cover changes identified within the study area over a 20 year period. / Thesis (M.A.)-University of KwaZulu-Natal, Durban, 2010.

In South Africa mangrove forests are located in estuaries from Kosi Bay in KwaZulu-Natal (KZN) to Nahoon Estuary in the Eastern Cape. The aims of this study were to determine the present state of mangroves in KwaZulu-Natal, by assessing the current population structure, the changes in cover over time and associated anthropogenic pressures. A second objective of this study was to determine the effect of harvesting on the population structure and sediment characteristics in the Mngazana mangrove forest. To determine if harvesting was sustainable at Mngazana Estuary; the growth and mortality rates and associated growth conditions were measured. Finally by using population modelling sustainable harvesting limits were determined by predicting the change in population structure over time. The study focussed on the KwaZulu-Natal province as a fairly recent study addressed mangrove distribution and status in the Eastern Cape Province. A historical assessment of all mangroves forests in KwaZulu-Natal (KZN) revealed that the potential threats to mangroves in South Africa include; wood harvesting, altered water flow patterns coupled with salinity changes, prolonged closed-mouth conditions and subsequent changes to the intertidal habitat. As a result mangroves were completely lost from eleven estuaries in KZN between 1982 and 1999 and a further two estuaries by 2006. Mangroves only occurred in those estuaries where the mouth was open for more than 56 percent of the time with the exception of St Lucia, where the mouth has been closed for longer but the mangrove communities have persisted because the roots of the trees were not submerged. All mangrove forests in KZN were regenerating in terms of population structure as they had reverse J-shaped population curves as well as high adult: seedling ratios. Kosi Bay and Mhlathuze Estuary were two of the larger forests that showed signs of harvesting (presence of tree or branch stumps), but the greatest threat to smaller estuaries seems to be altered water flow patterns due to freshwater abstraction in the catchments and the change of land use from natural vegetation to sugar-cane plantations. These threats affect the hydrology of estuaries and the sediment characteristics (particle size, redox, pH, salinity, temperature) of the mangrove forests. The environmental conditions under which the mangrove forests currently exist were determined for five species. Lumnitzera racemosa and Ceriops tagal exhibited a narrow range of conditions as these species are only found at Kosi Bay, while Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata were found to exist under a wider range of conditions. The growth rate and response to environmental conditions of the three dominant species were important to determine as these species are impacted by harvesting. Mangrove growth rates were measured at Mngazana Estuary in the Eastern Cape, the third largest mangrove forest in South Africa. Areas of this estuary where mangroves harvesting has occurred, show significant differences in sediment characteristics as well as changes in population structure in harvested compared to non harvested sites. The growth rate (in terms of height) of Avicennia marina individuals increased from seedlings (0.31 cm month-1) to adults (1.2 cm month-1), while the growth of Bruguiera gymnorrhiza stabilised from a height of 150 cm at 0.65 cm month-1. The growth of Rhizophora mucronata peaked at 0.72 cm month-1 (height 151-250 cm) and then decreased to 0.4 cm month-1 for taller individuals. Increases in diameter at breast height (DBH) ranged between 0.7 and 2.3 mm month-1 for all species. Some environmental variables were found to be important drivers of growth and mortality of individuals less then 150 cm. A decrease in sediment pH significantly increased the mortality of Avicennia marina seedlings (0-50 cm) (r = - 0.71, p<0.05) and significantly decreased the growth of Rhizophora mucronata and Bruguiera gymnorrhiza seedlings (r = -0.8, r = 0.52 – p < 0.05 respectively). At Mngazana Estuary, mortality of this species showed a positive correlation with sediment moisture content indicating that this species prefers drier conditions. The density of Rhizophora mucronata was significantly correlated to porewater temperature in Northern KZN as was the growth of adult (>300 cm) Rhizophora trees at Mngazana Estuary. Mortality of Avicennia marina individuals (51-150 cm) was related to tree density indicating intraspecific competition and self thinning. Selective harvesting of particular size classes of Rhizophora mucronata was recorded when comparing length of harvested poles (~301 cm) and the size class distribution of individuals. Taking into account the differences in growth rate for each size class for this species it will take approximately 13 years to attain a height of 390 cm which is the height at which trees are selected for harvesting at this estuary. This is 2.6 times slower than those individuals growing in Kenya. The feasibility of harvesting is dependent on the growth rate of younger size classes to replace harvested trees as well as the rate of natural recruitment feeding into the population. Different harvesting intensity scenarios tested within a matrix model framework showed that limits should be set at 5 percent trees ha-1 year-1 to maintain seedling density at > 5 000 ha-1 for R. mucronata. However harvesting of Bruguiera gymnorrhiza should be stopped due to the low density of this species at Mngazana Estuary. Harvesting of the tallest trees of Avicennia marina can be maintained at levels less than 10 percent ha-1 year-1. Effective management of mangrove forests in South African is important to maintain the current state, function and diversity of these ecosystems. Management recommendations should begin with determining the freshwater requirements of the estuaries to maintain the mouth dynamics and biotic communities and deter the harvesting of (whole) adult trees particularly those species that do not coppice. Further management is needed to ensure that forests are cleared of pollutants (plastic and industrial), and any further developments near the mangroves should be minimized.

In Florida, mangroves have responded to climate change by slowly migrating northward into traditional salt marsh habitat. However, little is understood about the relationships among mangrove growth form plasticity and environmental conditions. In addition, the effects of the mangrove northward expansion on pre-existing salt marsh communities are unknown, especially any influences of differences in tree morphology. The size, canopy structure, and root structure of the three mangrove species Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa were measured at six sites along the east coast of Florida. Structural equation modeling was used to evaluate the multivariate relationships between environmental and biotic variables. Mangrove growth form varied widely with environmental variables. The results of this study suggest that R. mangle expansion into salt marsh may rely on interactions with salt marsh and shading as well as on climatic variables, which has implications for future mangrove expansion northward in Florida. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Mangrove ecosystems thrive in (sub)tropical, intertidal areas where adaptations<p>like vivipary and the hydrochorous dispersal of propagules become an absolute<p>necessity. As propagule dispersal and early growth allow for the replenishment of<p>existing stands and colonization of new habitats, many authors recognize the<p>importance of these stages in structuring mangrove populations and communities.<p>However, when it comes to the actual propagule dispersal and recruitment<p>mechanisms, there is an apparent lacuna in the current understanding of<p>mangrove ecology. The period between the mature propagule falling from the<p>parental mangrove tree and the early growth of the established seedling, under<p>various possible circumstances, remains in the dark. In this study we focus on this<p>particular period by investigating both the places where these propagules end up<p>as the pathways their dispersal units follow. And we go one step further.<p><p>Mangrove forests are being destroyed worldwide at a threatening pace despite<p>their tremendous asset to coastal human communities and associated biological<p>species. The effect of human-induced (cutting and mangrove conversion to<p>aquaculture ponds) as well as indirectly and/or ‘naturally’ evolving disturbances<p>(sea level rise) on propagule hydrochory occupies an important place in this study.<p><p>Dispersal of water-buoyant propagules of the family Rhizophoraceae and<p>Acanthaceae (now including the Avicenniaceae) was studied in Gazi Bay (Kenya),<p>Galle and the Pambala-Chilaw Lagoon Complex (Sri Lanka). The study sites<p>differ both in tidal regime and vegetation structure, covering an interesting variety<p>of ecological settings to examine propagule dispersal. Field data and experiments<p>ranging from micro/ mesotopographical measurements and successive propagule<p>counts to hydrodynamic and propagule dispersal experiments were collected or<p>executed in situ.<p><p>Two main methodological approaches were employed. Firstly, the question on<p>mechanisms of propagule recruitment was addressed by statistically investigating<p>the effect of microtopography, top soil texture and above-ground-root complexes on<p>the stranding and self-planting of propagules (Chapter 2&3). Afterwards,<p>suitability maps were created using Geographical Information Systems (GIS) to<p>assess whether a particular mangrove stand has the ability to succesfully<p>rejuvenate. Furthermore, the effect of degradation (tree cutting) (Chapter 2&3),<p>sea level rise (Chapter 2&4) and microtopography-altering burrowing activities of<p>the mangrove mud lobster Thalassina anomala (Chapter 3), was incoporated in the<p>GIS-analyses. Secondly, the combined set-up of hydrodynamic modelling and<p>ecological dispersal modelling was developed to simulate propagule dispersal<p>pathways influenced by dispersal vectors (tidal flow, fresh water discharge, wind),<p>trapping agents (retention by vegetation or aerial root complexes) and seed<p>characteristics (buoyancy, obligated dispersal period) (Chapter 5&6). This type of<p>approach provided the possibility to explore propagule dispersal within its<p>ecological context, but was also applied to an implication of shrimp pond area<p>restoration (Pambala-Chilaw Lagoon Complex, Sri Lanka) (Chapter 5) and to<p>evaluate changes in propagule dispersal when sea level rises (Gazi Bay, Kenya)<p>(Chapter 6).<p><p>The main findings regarding propagule recruitment indicate that propagules are<p>not distributed equally or randomly within a mangrove stand, yet species-specific<p>distribution for anchorage occurs. Characteristics of the environment<p>(microtopography, top soil texture and above-ground root complex) influence<p>propagule recruitment in a way that complex root systems (e.g. pencil roots and<p>prop roots) facilitate the entanglement of dispersal units and a more compact soil<p>texture (like clay and silt) and a predominant flat topography creates suitable<p>areas for stranding and self-planting of propagules. This combines effects of<p>existing vegetation and abiotic factors on mangrove propagule establishment.<p>Since propagule dispersal is not solely determined by species-specific propagule<p>characteristics (e.g. buoyancy, longevity, etc.), I emphasize that propagule sorting<p>by hydrochory has to be viewed within its ecological context. Propagule retention<p>by vegetation and wind as a dispersal vector, deserve a prominent role in studies<p>on propagule dispersal. The significance of dense vegetation obstructing long<p>distance dispersal (LDD in its definition of this work), mainly in inner mangrove<p>zones, supports our main finding that propagule dispersal is largely a short<p>distance phenomenon. ‘Largely’ is here understood as quantitatively, not<p>excluding epic colonization events of rare but important nature.<p>In accordance with the Tidal Sorting Hypothesis (TSH) of Rabinowitz (1978a),<p>smaller, oval-shaped propagules were found to disperse over larger distances than<p>bigger, torpedo-shaped propagules. We can however not fully support the TSH<p>because (1) these differences are no longer valid when comparing between torpedoshaped<p>propagules of different sizes and (2) propagule dispersal is not always<p>directed towards areas more inland, but can be strongly concentrated towards the<p>edges of lagoons and channels<p><p>Anthropogenic pressure on mangrove ecosystems, more specifically clear-felling or<p>mangrove conversion to aquaculture ponds, imposes limitations on propagule<p>recruitment due to reduced propagule availability and a decrease in suitable<p>stranding areas where the architecture of certain root complexes, like prop roots<p>and pencil roots, function as propagule traps. These types of pressure appear to<p>have more severe consequences on propagule dispersal than the effect of sea level<p>rise on mangroves. Mangrove forests, which are not situated in an obviously<p>vulnerable setting, can be resilient to a relative rise in sea level if a landward shift<p>of vegetation assemblages and successful early colonization is not obstructed by<p>human-induced pressures. Also, and this renders mangrove forests vulnerable in<p>spite of their intrinsic resilience, when the ‘capital’ of forest is severely reduced or<p>impoverished as happens extensively worldwide, the ‘interest’ on this capital,<p>understood as propagule availability, delivery and trapping, will not allow them to<p>efficiently cope with sea level rise, putting sustainability of mangrove ecosystem<p>services and goods at risk.<p><p>In a larger framework of mangrove vegetation dynamics, knowledge on propagule<p>dispersal will benefit management strategies for the conservation of mangroves<p>worldwide, besides its fundamental interest to fully fathom the ecology of this<p>particular marine-terrestrial ecotone formation. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

This study addresses a core problem that was uncovered in records from coastal management monitoring initiatives on the eastern coast of Tanzania associated with the application and use of coastal monitoring indicators developed by external development partners for the coastal zone. These records suggest that local communities, who are key actors in participatory monitoring of coastal and marine resources, face many challenges associated with adapting and applying the said frameworks of indicators and monitoring plans. These indicators tend to be scientifically abstracted and methodologically reified; given prevailing contextual and socio‐cultural realities amongst them. The research project addresses the following key research question: How can processes of abstraction, conceptualisation, and representation of TEK contribute to the development of coastal management indicators that are less reified, more contextually and culturally congruent, and which may potentially be used by resource users in the wider social learning process of detecting trends, threats, changes and conditions of mangrove and fisheries resources? In response to the contextual problem and the research question, the study employs processes of abstraction and experiential learning techniques to unlock knowledge that local communities have, as an input for underlabouring existing scientific indicators on the Eastern coast of Tanzania. The research is constituted as critical realist case study research, involving two communities on the eastern coast of Tanzania, namely the Moa and the Boma communities (in Mkinga coastal district). Overall, the study involved 37 participants in a series of interviews, focus group discussions, and experiential learning processes using visualised data, and an experiential learning intervention workshop, and follow‐ups over a period of 3 years. The study worked with mangroves and fisheries to provide focus to the case study research and to allow for in‐depth engagement with the assumptions and processes associated with indicators development and use. Through the above mentioned data generation processes, critical realist analysis, and experiential learning processes involving abstraction and representation of traditional ecological knowledge held by mangrove restorers and fishers in the study areas, the study uncovers possible challenges of adapting and applying scientific indicators in participatory monitoring of a mangrove ecosystem. Using ampliative modes of inference for data analysis (induction, abduction and retroduction) and a critical realist scientific explanatory framework known as DRRREI(C) (Resolution, Re‐description, Retrodiction, Elimination, Identification, & Correction) the study suggests a new approach that may lead to the development of a framework of indicators that are less reified, more congruent to users (coastal communities), and likely to attract a wider context‐based social learning which favours epistemological access between scientific institutions (universities inclusive), and local communities. It attempts to establish an interface between knowledge that scientific institutions produce and the potential knowledge that exists in local contexts (traditional ecological knowledge), and seeks to widen and improve knowledge sharing and experiential learning practices that may potentially benefit coastal and marine resources in the study area. As mentioned above, the knowledge and abstraction processes related to the indicators development focussed on the mangrove ecosystem and associated fisheries, as engaged in the two participating communities in the eastern coast of Tanzania. The specific findings are therefore limited by the case boundaries, but the methodological process could be replicated and used elsewhere. The study’s contributions are theoretical and methodological, but also social and practice‐centred. The study brings into view the need to consider the contextual relevance of adapted knowledge, the capacity or ability of beneficiaries to adapt and apply scientific models, frameworks or tools, and the potential of local knowledge as an input for enhancing or improving monitoring of mangroves and mangrove‐based fisheries. Finally, the study comes up with a framework of indicators which is regarded by the coastal communities involved in the study as being less reified, more contextually and culturally congruent, and which may potentially be used in detecting environmental trends, threats, changes and conditions of mangrove and fisheries resources, and attract wider social learning processes.