Solutions for restoring and protecting the threatened seagrass Posidonia australis

Download files
Access & Terms of Use
open access
Copyright: Ferretto, Giulia
Altmetric
Abstract
Seagrasses create a critical habitat for diverse communities and support vital ecosystem functions and services in coastal environments. The installation of artificial structures and urbanisation are key drivers of ecological change in coastal environments, often fragmenting and altering natural habitats with cascading effects on local ecosystem services. Posidonia australis is a slow-growing seagrass, endemic to Australia, that forms extensive meadows in sheltered temperate estuaries which are popular areas for boating activities and aquaculture. P. australis in New South Wales is particularly susceptible to impacts derived from boating activities, including habitat damage from boat moorings, and from structures associated with aquaculture industries. In recent decades, major losses have been recorded, with poor rates of recovery leading to the Endangered listing of P. australis in some estuaries in New South Wales. Although alternative (i.e., more ‘environmentally friendly’) designs of boat moorings and oyster aquaculture have been developed with the aim to reduce impacts on seagrass, more research is needed to combine those methods with the legal protection of P. australis. In this thesis, I tested methods to restore and protect the threatened seagrass P. australis and quantified the relationships between the meadow structure and ecosystem functions. Initially, I developed an innovative restoration procedure to re-establish P. australis transplants within old boat mooring scars, using naturally-detached fragments collected from the shore by citizen scientists. In New South Wales, the options for obtaining material to restore P. australis are limited due to the low seed production and the protected and declining status of seagrass meadows that could provide donor material. Survival after one year was significantly greater for those planted in June (54 %) than in January (31 %) and many surviving fragments had produced new shoots. Collected fragments with less dead leaf tissue (necrosis) and with more (> 3) shoots were the most likely to survive. I then used field experiments to quantify how three of the most common oyster cultivation methods in NSW (trays, longline baskets and floating bags), which are commonly located over seagrass, affect P. australis. Trays and longline baskets significantly reduced the amount of light available to the seagrass, which in turn compromised P. australis photosynthetic efficiency leading to 4-fold declines in shoot density after only 3 months. Conversely, floating bags caused no decline in shoot density. Lastly, as differences in seagrass extent can have cascading effects on associated biodiversity, I used a seascape approach to measure whether ecosystem functions and processes vary based on the habitat complexity of P. australis meadows. I found that faunal communities, rates of predation and sediment erosion all related to levels of meadow fragmentation and density, with lower erosion in denser areas and more fish species in vegetated areas far from meadow edges. Overall, this thesis combines restoration and conservation approaches to optimise restoration and reduce human impacts on coastal seagrass beds while engaging local communities to increase awareness.
Persistent link to this record
Link to Publisher Version
Link to Open Access Version
Additional Link
Creator(s)
Editor(s)
Translator(s)
Curator(s)
Designer(s)
Arranger(s)
Composer(s)
Recordist(s)
Conference Proceedings Editor(s)
Other Contributor(s)
Corporate/Industry Contributor(s)
Publication Year
2022
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
Files
download public version.pdf 5.65 MB Adobe Portable Document Format
Related dataset(s)