University of Groningen
The future of seagrass ecosystem services in a changing world James, Rebecca
DOI:
10.33612/diss.132586601
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Publication date: 2020
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James, R. (2020). The future of seagrass ecosystem services in a changing world. https://doi.org/10.33612/diss.132586601
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Summary
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Summary
Seagrass meadows strongly impact chemical and physical processes, and support a rich diversity of taxa within the Caribbean coastal environment. Through their metabolism, seagrasses alter the carbonate chemistry of the surrounding seawater, which can help buffer vulnerable organisms from ocean acidification. In addition, the dense canopies of seagrass meadows attenuate waves and stabilise sediment, thereby providing coastal protection services. These coastal protection services are becoming increasingly important as coastal flooding and erosion is exacerbated by sea level rise. Unfortunately, global degradation of seagrass meadows is threatening the provision of these ecosystem services. By building an understanding of the functioning of seagrass ecosystems and their provision of important ecosystem services (Chapter 2-5), this work aims to identify how these ecosystem services will be altered by global change (Chapter 6) and subsequently, how seagrass-dominated coastal ecosystems may change in the future (Chapter 6 & 7).
The removal and release of CO2 through photosynthesis and respiration by seagrasses leads to
temporal pH fluctuations within seagrass meadows. Monitoring of these pH fluctuations at sites with contrasting hydrodynamic regimes, displayed how the pH within seagrass-dominated regions varies both spatially and temporally (Chapter 2). At the outer edge of tropical bays, small diurnal pH fluctuations of 0.11 exist, driven by the metabolism of the coral reefs and algae living on these reefs. Further into the bays where dense seagrass meadows are present, the diurnal pH fluctuations increase in magnitude, reaching a maximum pH range of 0.3. The magnitude of these pH changes is driven by the density of the seagrass vegetation and the counteracting effect of water motion (Chapter 2). This high temporal and spatial pH variability has implications for the response to ocean acidification of organisms living within vegetated coastal regions.
The sediment stabilisation capacity of Caribbean seagrass species was measured directly with specially-designed portable field flumes (Chapter 3). Late-successional seagrass species (i.e. Thalassia testudinum) were identified as providing effective coastal protection services. By stabilising sediment through their dense canopy that deflects the flow away from the sediment surface, and by their robust root network, T. testudinum prevents erosion on the beach shoreface. Field surveys and numerical simulations display how T. testudinum meadows are incredibly effective at attenuating waves during extreme storms, and thereby, minimising coastal erosion during extreme events (Chapter 5). These coastal protection services provided by the native Caribbean seagrass meadows cultivate into the long-term maintenance of stable Caribbean sandy beaches (Chapter 4). Intensive megaherbivore grazing, invasion by fast-growing opportunistic seagrasses and intensifying coastal infrastructure, however, greatly increase the vulnerability of Caribbean beaches to coastal erosion (Chapter 3 & 4). This
Summary
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erosion threatens the stability of Caribbean beaches, which the region is highly dependent on for tourism and coastal flood protection (Chapter 4).
Knowledge on the pH variability and coastal protection services provided within seagrass-dominated bays, was integrated with simulations of future hydrodynamic scenarios, to examine the resilience of these ecosystem services to the future changes of sea level rise and habitat degradation (Chapter 6). The fringing coral reef was found to have the strongest influence on the hydrodynamic forces within tropical bays, and if the fringing reef remains, the conditions within the bay will remain relatively stable, even with a 0.87 m rise in sea level. If, however, the fringing coral reef degrades, a strong increase in hydrodynamic forces entering the bay will greatly increase sediment instability across the bay (Chapter 6). Degradation of the seagrass meadows themselves will leave the bay ecosystem vulnerable to ocean acidification and coastal erosion and flooding. It is, therefore, vital that the natural coastal ecosystems of fringing coral reefs and seagrass meadows are maintained, to ensure the resilience of tropical coastal regions to climate change.
