Browsing by Author "Watson, Katie Margaret"

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    Exploring the restoration of Zostera capensis in Langebaan Lagoon: ecological, molecular and physiological perspectives
    (Stellenbosch : Stellenbosch University, 2024-03) Watson, Katie Margaret; Pillay, Deena; Von der Heyden, Sophie; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Despite being one of the most valuable natural systems globally, seagrass meadows are also among the most threatened due to global climate change and localised threats. There is growing concern that the ecosystem functions seagrasses perform will be reduced or lost altogether without intervention, as is the case for the endangered Cape dwarf-eelgrass (Zostera capensis) in South Africa, including its declines in Langebaan Lagoon, the focus of this study. Although fast-growing, Z. capensis does not colonise new areas quickly and is highly threatened due to anthropogenic impacts, resulting in population declines and local extinctions. As such, management interventions through integrating seagrass restoration as part of a resilience-based management strategy are urgently needed. However, seagrass restoration has previously been viewed as an unpredictable management strategy, with a mixed history of success. The principal aim of this PhD was to explore the restoration potential of Z. capensis, employing ecological, molecular, and physiological methods. The first chapter aimed to address issues associated with transplantation by investigating Z. capensis restoration using different donor materials (cores and anchored shoots) planted in different spatial arrangements across several sub-sites within Oestewal, Langebaan Lagoon. After 18 months of monitoring, ~58 % plots survived across all treatments, but temporal persistence and area cover increased in transplant plots using cores in a dense pattern towards the upper shoreline, expanding by >400 % in some instances. To identify areas to prioritise for future restoration efforts, Chapter 2 employed habitat suitability modelling (HSM) to explore how environmental data and Z. capensis distribution over time shape habitat suitability at local scales. Remote sensing using supervised semi-automated classification to predict past and current Z. capensis distribution, was used in combination with the preliminary transplant suitability index (PTSI), identifying several priority areas for restoration. The HSM model was validated through post hoc data from the restoration trial in Chapter 1. In Chapter 3, a controlled mesocosm experiment was conducted using two genomically divergent Z. capensis populations, found naturally occurring in Langebaan Lagoon, exposed to a simulated marine heatwave (MHW) event. The experimental procedure allowed the identification of photophysiological responses as well as transcriptomic mechanisms involved in the thermal tolerance of Z. capensis, with the successful activation and regulation of heat-responsive genes involved in plant defence and histone methylation in heated plants potentially supporting processes involved in short-term heat acclimation. Under global-change scenarios, gaining insights into the transcriptional and photophysiological responses of increasing thermal extremes worldwide, such as MHWs, is crucial to understanding the responses of foundational species, with important implications for restoration and conservation management. Chapter 4 presents a review of gene expression studies in seagrasses globally, providing insights into how these studies have the potential to revolutionise seagrass restoration through project co-creation. In conclusion, this thesis explored ecological, molecular, and physiological approaches to enable practitioners to incorporate targeted seagrass conservation and restoration measures as an integral part of Z. capensis management across southern Africa.