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Towards an understanding of mangrove diversity in Australia

Cresswell, Ian (2012) Towards an understanding of mangrove diversity in Australia. PhD thesis, Murdoch University.

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The key findings of this thesis link mangrove diversity with the diversity of abiotic environments and, for the first time, provides a consistent method for the development of a comprehensive scientific framework for the management of mangrove ecosystems at national level. In Australia (and globally) a lack of information on the different mangrove habitats that support the diverse range of mangrove ecosystems has inhibited both management and conservation of mangrove ecosystems. Currently there is no agreed and commonly used national classification scheme for mangrove information. This gap weakens future conservation and sustainable development of the Australian coastline. This thesis addresses that gap in knowledge.

The physical framework of the Australian coast forms the habitat template in which mangrove diversity develops. The key hypothesis examined is that an understanding of the abiotic setting within which mangroves are found markedly improves an understanding of the distribution and diversity of mangrove ecosystems.

To test that hypothesis, detailed examination of the four overarching physical drivers that shape the Australian continental edge: geology, physiography, climate and oceanography, was undertaken to create a comprehensive picture of the abiotic coastal environment. This showed that coastal, fluvial, and hydrological processes that lead to coastal landform development form the basis for understanding the various coastal landforms and mangrove habitats developed along the Australian coast. The results demonstrate that physical drivers and coastal process do shape the distribution of mangrove species, and how mangrove vegetation is developed, maintained, changed or lost. Inter‐relationships between these overarching physical drivers provide a classification of Australia’s coast into major coastal sectors, including those which do not support mangroves. To elaborate the results, a description of each sector containing mangroves and the types of mangrove habitats present is provided.

Mangrove diversity is not simply variation in floristics (species richness) but also must include structural and physiognomy diversity. An individual species of mangrove may perform various ecosystem roles in different physical settings. This concept is elaborated through constructing eight hypothetical expressions of mangrove diversity examining the changes in mangrove habitats under increasing complexity of tidal and climate influence, showing how the interaction between tidal, climate and environmental gradients results in different mangrove expression around the Australian coast.

Building on the interactions between abiotic and biotic diversity, seeking ways and means to improve mangrove conservation in Australia, lead to ideas for the development of a mangrove focused national conservation strategy. A set of three criteria is put forward to identify the significance of mangrove sites globally, nationally and/or regionally (sub‐nationally). Besides these practical approaches, an assessment of each State and Territory’s mangrove management and conservation mechanisms shows the scope of existing policies and conservation strategies, and reveals little coordination of mangrove conservation or management issues at the national level, or between the jurisdictions. Building on these findings, and in the framework of the proposed national conservation strategy, a series of recommendations are made to improve the collection and access to mangrove information, including through the implementation of a national level data and information plan providing standards for biophysical and management information on mangroves.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Bridgewater, Peter, Dell, Bernard and Semeniuk, Vic
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