Exploring the restoration of Zostera capensis in Langebaan Lagoon: ecological, molecular and physiological perspectives

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dc.contributor.advisorPillay, Deenaen_ZA
dc.contributor.advisorVon der Heyden, Sophieen_ZA
dc.contributor.authorWatson, Katie Margareten_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Botany and Zoology.en_ZA
dc.date.accessioned2024-02-08T09:26:50Z
dc.date.accessioned2024-04-27T00:34:12Z
dc.date.available2024-02-08T09:26:50Z
dc.date.available2024-04-27T00:34:12Z
dc.date.issued2024-03
dc.descriptionThesis (PhD)--Stellenbosch University, 2024. en_ZA
dc.description.abstractENGLISH 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.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Ten spiyte dat die teen van die mees waardevolle natuurlike sisteme ter wêreld is, is seegras ook die mees gedreigde as gevolg van globale klimaatsverandering en plasslike bedreigings. Daar is toenemende kommer dat die ekosisteem funksies wat deur seegras voorsien word, verminder of heeltemal verlore sal gaan sonder ingrying, soos in die gevel met die bedreidge Kaapse dwerg-eelgras (Zostera capensis) in Suid Afrika, insluitend die populasie vermindering in Langebaan Lagoon, wat die fokus area is van die studie. Alhoewal dit vining-groeiend is, kan Z. capensis nie vining nuwe areas koloniseer nie, en is hoogs bedreig as gevolg van antropogeniese invloed, wat lei tot `n afname in populasie en plaaslike uitsterwings. Daarom is bestuur ingrypings, duer die integrasie van seegras restorasie, as deel van `n veerkragtige-gebaseerde bestuur strategie dringend nodig. In die verlede was seegras oes egster gesien as `n onvoorspelbare bestuurs strategie, met gemengde resultate van sukses. Die primêre doel van hierdie PhD was om die oes potentiaal van Z. capensis te ondersoek, deur ekologiese, molekulêre en fisiologiese metodes te gebruik. Die eerste hoofstuk is gemik daarop om kwessies wat geassosieer word met die oes en oorplanting van Z. capensis te ondersoek , waar verskillende skenker materiale (kerne en geankerde lote) geplant is in verskillende ruimtelike rangskikkings oor verskeie sub-areas in Oesterwal, Langebaan Lagoon. Na 18 maande van monitering, het ~58 % van die eenheid oorleef vir al die eksperimentele behandelinge, maar temporal persistence en area dekking het toegeneem in oorplantings waar kerne in `n digte formasie geplan was nader aan die boonste kuslyn, waar dit met >400 % toegeneem het in sommige gevalle. Om prioriteit areas te identifseer vie die toekomstige oes van seegras, het Hoofstuk 2 van habitat geskiktheid modellering (HSM) gebruik gemaak om te ondersoek hoe omgewings data en Z. capensis distribusie oor tyd habitat geskiktheid beïnvloed op `n plasslike skaal. Afstandswaarneming deur semi-automatiese klassifikasie om geskiedkundige en toekomstige Z. capensis distribusie te voorspel, was gebruik in kombinasie met die voorlopige oorplantingsgeskiktheidsindeks (PTSI), om verskeie prioriteits areas vir die oes van seegras te identifiseer. Post hoc data van die seegras restorasie eksperiment in Hoofstuk 1, het die HSM-model geverifieer. In Hoofstuk 3 was `n gekontrolleerde mesokosmos eksperiment uitgevoer met twee uiteenlopende genetiese Z. capensis populasies wat natuurlike groei in Langebaan Lagoon. In die eksperiment was die twee populasies blootgestel aan `n kunsmatige mariene hittegolf (MHW). Die eksperimentele procedure het toegelaat vir die identifiseering van fotofisiologiese reaksies as ook transkriptomiese meganismes wat betrokke is in die termiese toleransie van Z. capensis. Die prosedure het ook hitte-responsiewe gene wat betrokke is in plant verdediging en histone metilering in plante onder verhitte kondisies, geaktiveer en reguleer. Hierdie reaksies ondersteun prosesse wat potensieel betrokke is in kort termyn hitte aklimatisering. Om insigte te try oor transkripsie en fotofisiologiese reaksies as gevolg van toenemende termiese esktreme wêreldwyd, soos MHW, is dit belangrik om die reaksies van fundamentele spesies te verstaan, vir die optimale restorasie, bewaring en bestuur van seegras. Hoofstuk 4 voorsien `n hersienning van studies gemik op die uitdrukking van gene inseegras popularsies wêreldwyd, wat belangrike insig gee tot die potentiaal van seegras restorasie deur middel van mede-skepping projekte. In afsluiting, hierdie proefskrif het ekologiese, molekulêre en fisiologiese benaderings verken om beamptes instaat te stel om geteikende seegras bewaring en restorasie maatreëls as `n integrale deel van Z. capensis bestuur in suidelike Afrika te inkorporeer.af_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentxxvi, 240 pages : illustrations(some color), mapsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130629
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshSeagrasses -- Climatic factorsen_ZA
dc.subject.lcshZostera capensis -- Ecology -- South Africa -- Langebaan Lagoonen_ZA
dc.subject.lcshSeagrasses -- Transplanting -- Environmental aspectsen_ZA
dc.subject.lcshGrassland restoration -- South Africaen_ZA
dc.subject.lcshEelgrass -- Effect of stress onen_ZA
dc.subject.lcshHabitat suitability index modelsen_ZA
dc.subject.lcshPlant gene expressionen_ZA
dc.subject.lcshSeagrass restoration -- Monitoringen_ZA
dc.subject.nameUCTDen_ZA
dc.titleExploring the restoration of Zostera capensis in Langebaan Lagoon: ecological, molecular and physiological perspectivesen_ZA
dc.typeThesisen_ZA
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