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Fast-tracking succession: Utilising Halophila ovalis to improve the survival of climax seagrass transplants in Western Australia

Parker, Joshua G. (2020) Fast-tracking succession: Utilising Halophila ovalis to improve the survival of climax seagrass transplants in Western Australia. Honours thesis, Murdoch University.

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Abstract

Seagrasses provide many important ecosystem services and functions, benefiting a wide range of marine organisms and the livelihoods of many people around the world. Unfortunately, the global extent of seagrasses worldwide has declined significantly as a result of anthropogenic impacts in conjunction with more intense and frequent natural impacts, exacerbating the loss. There have been many attempts around the world and more recently in Western Australia to restore degraded and damaged seagrass meadows. Common transplanting methods involve vegetative fragments or seeds/seedlings which are planted either directly into bare substrate or together with artificial substrate stabilisers such as mesh mats. These methods have displayed mixed results and proved to be very costly and slow.

Recent thinking in seagrass rehabilitation involves “compressed succession” which promotes fast-growing colonising species to spread into disturbed areas, then planting slow-growing climax species into these areas. In this study, plagiotropic sprigs of Posidonia australis (N = 108) were planted into areas containing either Halophila ovalis, P. australis or bare sand in Jervoise Bay, Perth and monitored weekly from April to August 2020. Similarly, orthotropic sprigs of Posidonia coriacea (N = 120) were planted into areas containing either H. ovalis, P. coriacea or bare sand in Bateman Bay, Ningaloo Reef and monitored fortnightly from June to August 2020. We hypothesised that if the colonising species H. ovalis was present, then sprig survival would be improved.

The study in Jervoise Bay found that over the course of five months, approximately 60 % of sprigs survived overall. Sprig survival was improved in treatments that featured existing seagrass growth. Sprig survival was only improved by 11 % when transplanted into an existing meadow of P. australis compared to a meadow of H. ovalis. Similarly, the study in Bateman Bay found that over the course of seven weeks, approximately 88 % of sprigs survived overall. Sprig survival was relatively similar in all treatments, however greater survival rates occurred in treatments that featured existing seagrass growth. Even though H. ovalis is smaller in structural form than P. australis and P. coriacea, the rapid growth rate of H. ovalis makes it appealing to transplant into, making it a viable “compressed succession” pathway. Overall, the results support the idea that existing seagrass meadows can provide protection for transplants, improving their survival.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
United Nations SDGs: Goal 14: Life Below Water
Supervisor(s): van Keulen, Mike
URI: http://researchrepository.murdoch.edu.au/id/eprint/61173
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