ORCID

Abstract

Within the space of a decade, intertidal sediments in the Tamar estuary, South West England, have undergone a shift from unvegetated mudflats to dense perennial seagrass habitat. Yet despite the increasing prevalence of intertidal seagrass meadows in the South West, there are large knowledge gaps relating to intertidal meadow biodiversity, function and ecosystem service provision, particularly within the context of the estuarine meadows of the South West: as such we do not fully understand the implications of this recent colonisation within the Tamar. This study aims to characterise the spatial expansion of these newly-established Zostera marina meadows using Earth observation platforms. It further aims to define the spatio-temporal variability of the organic carbon (Corg) stocks through analysis of sediment cores, and the biodiversity of the macrobenthic assemblage within these new meadows through infauna cores, comparing results with samples collected from an established Zostera noltii meadow within the Kingsbridge Ria, and unvegetated estuarine mudflats.This research evidences, using remote sensing techniques, the spatio-temporal expansion of intertidal Z.marina meadow colonising 25ha of previously unvegetated mudflat within the Tamar estuary between 2011 and 2023. Investigations into the Corg stocks of intertidal meadows in the South West showed that cumulatively, the sampled meadows do not hold higher organic carbon stocks with then top 50cm of sediment than adjacent unvegetated mudflat. Organic carbon stocks in the Tamar meadows (60-80 MgCha-1) were similar to other published southern UK intertidal meadows. The Z.noltii meadow carbon stock from the Kingsbridge estuary was below average for this species (50-60 MgCha-1). All sampled cores from vegetated and unvegetated habitat showed high spatio-temporal variability in relatively short (6 month) time scales with sometimes substantial changes in MgCha-1 down to 50cm depth, between winter and summer seasons (Z. marina meadow one: ~20 MgCha-1Δ, Z. marina meadow two: ~1 MgCha-1Δ, Z.noltii meadow: ~10 MgCha-1Δ). There was a negative relationship between grainsize and increased % cover of seagrass across all meadows. When looking at the macrobenthic assemblage intertidal meadows were not more biodiverse, nor was the macrobenthic assemblage distinct from unvegetated mudflat, this may have been an artifact of sample design. Composition of the macrobenthic assemblage did however significantly differ between seagrass meadows, and although different, the species found in all three sampled meadows were typical of those recorded in other temperate intertidal Zostera spp. meadows within the UK, and across the English Channel. The Z.noltii meadow was more biodiverse and species rich (~12.5 S 33cm-2 core) than the emergent Z. marina meadows (~10.5 S 33cm-2 core). Shoot density was the most significant localised predictor of macrobenthic assemblage across all meadows, however salinity was also likely a significant driver of assemblage differences between the Tamar and Kingsbridge estuaries.This thesis adds to our understanding of the spatiotemporal dynamics of intertidal seagrass meadows, and their associated blue carbon stocks and macrobenthic assemblage, specifically in relation to their roles within estuaries in South West England. It therefore has important implications for estuarine management of intertidal seagrass meadows, and contributes to the wider scientific literature on this topic.

Awarding Institution(s)

University of Plymouth

Award Sponsors

Marine research Plymouth Alliance, Plymouth Marine Laboratory, Marine Biological Association

Supervisor

Melanie Austen, Martin Attrill, Dan A. Smale, Lauren Biermann

Keywords

Coastal Ecology, Blue Carbon, Biodiversity, Seagrass, Earth Observation

Document Type

Thesis

Publication Date

2026

Embargo Period

2026-01-16

Deposit Date

January 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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