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Stocks in Seagrass Posidonia Australis and the Impact of Historical Quantifying ‘blue carbon’ stocks in seagrass Posidonia australis and the impact of historical anthropogenic disturbance in Western Australia. Emma Moulton Murdoch University School of Veterinary and Life Sciences 2018 ii Declaration “I declare this thesis is my own account of my research and contains as its main content, work which has not been previously submitted for a degree at any tertiary education institution.” Emma Moulton. i Abstract Recent research into coastal ecosystems have highlighted the importance of seagrass meadows in their ability to efficiently capture and store carbon into the sediment, however meadows are in decline. This study aims to identify local organic carbon stocks in the aboveground and belowground biomass of the species Posidonia australis whilst comparing effects of human disturbance. Mangles Bay in Cockburn Sound was chosen as a degraded bay indicated by high human use, such as boating and industrial effluent, while Shoalwater Bay was chosen due to its location in a marine sanctuary. A total of 32 samples across 2 bays were sampled in-meadow for meadow characteristics and core samples containing the whole plant and sediment. Three locations were collected for bare sediment outside the meadows of each bay. Samples were dried at 70°C and burnt at 400°C using loss on ignition method to determine carbon content. Organic carbon per hectare was found to be higher overall in Mangles Bay, with a substantial contribution from the carbon stored in the sediment (34.81 ±4.45 Mg Corg per ha). Aboveground biomass in both bays had higher overall percentage carbon than all other categories sampled. True detrital matter in Shoalwater Bay had significantly higher percent carbon and carbon per hectare (5.71 ±4.83 Mg Corg per ha) values. Percent carbon was also highest in the sediment at 2.5 m depth in both bays. Low flushing in Mangles Bay is thought be the primary cause of higher carbon content in the sediment, though it is not significantly higher (P = 0.337). Overall anthropogenic disturbance in each bay had little impact on current Posidonia australis meadow carbon stocks in the aboveground and belowground. ii Acknowledgements I thank my supervisors Dr Jennifer Verduin and Dr Joe Fontaine for guiding me every step of the way and doing their best part to read over my drafts and give comments back to me promptly. I also thank Ian Dapson and Mark Thiele for working hard as my dive buddies and in lab maintenance. I thank Steve Goynich for being my skipper and fixing the NTC. Irene Zhang, Kieran Bronx Claudia Mueller and Aiden Clarke for volunteering to be my dive buddies. You have all helped hugely with my sample collection. iii Table of Contents Declaration.............................................................................................................................................. i Abstract .................................................................................................................................................. ii Acknowledgments ................................................................................................................................ iii List of Figures ....................................................................................................................................... vi List of Tables ........................................................................................................................................ vi 1. Introduction .............................................................................................................................. 1 2. Methods ................................................................................................................................... 11 2.1 Study Area .......................................................................................................................... 11 2.2 Coastal Morphology .......................................................................................................... 14 2.3 Study Design ..................................................................................................................... 14 2.4 Data collection .................................................................................................................. 15 2.5 Sample processing and statistical analysis ....................................................................... 18 i. Sample Processing in the lab ....................................................................................... 18 ii. Statistical Analysis and Calculations ............................................................................ 19 3. Results ..................................................................................................................................... 21 3.1 Meadow dynamics ............................................................................................................. 21 3.1.1 Shoot density, biomass and growth ............................................................................. 21 3.2 Organic carbon content .................................................................................................... 22 3.2.1 Organic carbon distribution ...................................................................................... 22 3.2.2 Percent organic carbon .............................................................................................. 23 3.2.3 Carbon per hectare .................................................................................................... 25 3.2.4 Carbon by depth ......................................................................................................... 26 3.2.5 Total organic carbon .................................................................................................. 27 4. Discussion ............................................................................................................................... 28 4.1 Meadow dynamics ............................................................................................................. 28 4.1.1 Shoot Density .............................................................................................................. 28 4.1.2 Shoot Biomass ............................................................................................................ 27 4.1.3 Growth rate ................................................................................................................ 28 4.2 Organic carbon content .................................................................................................... 29 4.2.1 Organic carbon distribution ...................................................................................... 29 4.2.2 Percent organic carbon .............................................................................................. 30 4.2.3 Carbon per hectare .................................................................................................... 32 4.2.4 Carbon by depth ......................................................................................................... 35 iv 4.3 Limitations .................................................................................................................... 40 4.4 Validation of the Hypothesis ......................................................................................... 41 5. Conclusion .............................................................................................................................. 41 6. References ............................................................................................................................... 43 7. Appendix ................................................................................................................................. 50 v I. List of Figures Figure 1: Distribution of seagrasses in relation to temperature zones (blue and red scale) and species richness (green scale, where dark green has the most number of species). Map inspired by Orth et al. (2006), Green and Short 2003, and Devault and Pascaline (2013). ……………....6 Figure 2: Aerial photo of the study area MB and SW off the coast of Point Peron on the Western Australian mainland. …………………………………………………………………………11 Figure 3: Samples arranged in five transects wide and four selected depths to cover the range of conditions in the bays. A= Mangles Bay, B=Shoalwater Bay (MB N=23, SW N=17). …….16 Figure 4: Photographs of field sampling and equipment. A) Posidonia australis shoot and a sediment core sample. B) PVC hand-corer, to take a sediment core sample. In a Posidonia australis seagrass meadow. C) Set up for growth rates in Posidonia australis meadow smothered by high filamentous algal growth in Mangles Bay. D) Metal sediment corer with serrated teeth, used for taking in-meadow core samples……………………………………..18 Figure 5: Mean percentage carbon and megagrams per ha of Corg from both bays in Posidonia australis in the summer. Note: left values for percentage carbon are the means derived from Mangles Bay while values on the right are means obtained from Shoalwater Bay. Image by Tracey Saxby, IAN. …………………………………………………………………………..22 Figure 6: Mean percent organic carbon (with SE) of A) living and dead plant biomass and B) the sediment…………………………………………………………………………………..24 Figure 7: Percentage sedimentary organic carbon by depth in Mangles Bay and Shoalwater Bay, with SE………………………………………………………………………………………..25 Figure 8: Percentage sedimentary organic carbon by depth in Mangles Bay
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