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An empirical evaluation of Posidonia australis (R. Br.) Hook f. restoration in Western Australia: Development of a decision-based restoration framework

Campbell, Marnie Lyn (2000) An empirical evaluation of Posidonia australis (R. Br.) Hook f. restoration in Western Australia: Development of a decision-based restoration framework. PhD thesis, Murdoch University.

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The loss of biodiversity is currently recognised as one of the greatest threats to continued ecosystem function. In terrestrial habitats this has been well researched and publicised resulting in active restoration and mitigation efforts. However, in marine environments the current efforts are less effective. Seagrasses are widely recognised as fundamental species in forming the basis of marine trophic food webs, binding sediments, providing habitat structure, shelter, and nurseries for fish and crustaceans and increasing the activity and movement of several active molecules and nutrients. Despite this crucial role, seagrass losses world-wide continue due to land reclamation, building of marinas and port facilities, eutrophication due to rural and urban runoff, inshore dumping of pollutants and dredging. While nations have legislated seagrass mitigation, no effective means of establishing new seagrass or restoring damaged meadows exist at present.

This dissertation examines current efforts world-wide to elucidate a common framework for identifying the crucial elements of a restoration plan, which include site selection, transplant unit and technique and habitat enhancement. Posidonia australis was identified as one of the dominant meadow forming species in Western Australia and therefore was selected to investigate the utility of this framework. An empirical examination of site selection was undertaken to determine a potential transplant site for Posidonia australis. Critical factors examined were light requirements, burial and handling disturbance and substrate preference. Based upon this evidence, Success Bank was found to be optimal, with high light levels (> 5% surface irradiance), fair water quality, no burial period, low-mid water movement and a sand substrate. Sites at Carnac Island and Woodman Point were rejected because they did not meet these fundamental criteria.

Transplant unit and technique were evaluated for Posidonia australis. This species produces large numbers of seed that have a high viability (91%) but few seedlings actually establish (< 3%). During the course of this project, natural vegetative recruitment was observed in the field with 31% of natural vegetative propagules settling and growing (0.78 mm d-1). Field rhizomes were also observed to extend at rates of 1.04 mm d-1. Based upon these findings P. australis vegetative propagules (plugs) were selected as the most appropriate transplant unit.

Habitat enhancement techniques are an optional component of a restoration activity and may significantly increase transplant success. In order to reduce water movement at the selected transplant site, the use of artificial seagrass mats was experimentally evaluated. Artificial seagrass mats were found to increase plug survival and rhizome elongation. In addition artificial seagrass mats reduced the variability in accretion and erosion of sediments. In the presence of habitat enhancement, up to 50% of seagrass plugs survived, with 39% exhibiting rhizome extension. Based on these findings a decision-based framework for seagrass restoration is presented with a discussion of future applications.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
United Nations SDGs: Goal 14: Life Below Water
Supervisor(s): Paling, Eric
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